Iohexol plasma clearance measurement protocol standardization for adults: a consensus paper of the European Kidney Function Consortium.

International consensus supports the development of standardized protocols for measured glomerular filtration rate (mGFR) to facilitate the integration of mGFR testing in both clinical and research settings. To this end, the European Kidney Function Consortium convened an international group of experts with relevant experience in mGFR. The working group performed an extensive literature search to inform the development of recommendations for mGFR determination using 1-compartment plasma clearance models and iohexol as the exogenous filtration marker. Iohexol was selected as it is non-radio labeled, inexpensive, and safe, can be assayed at a central laboratory, and the other commonly used non-radio-labeled tracers have been (inulin) or are soon to be (iothalamate) discontinued. A plasma clearance model was selected over urine clearance as it requires no urine collection. A 1 compartment was preferred to 2 compartments as it requires fewer samples. The recommendations are based on published evidence complemented by expert opinion. The consensus paper covers practical advice for patients and health professionals, preparation, administration, and safety aspects of iohexol, laboratory analysis, blood sample collection and sampling times using both multiple and single-sample protocols, description of the mGFR mathematical calculations, as well as implementation strategies. Supplementary materials include patient and provider information sheets, standard operating procedures, a study protocol template, and support for mGFR calculation.

Clinical validation of the novel fluorescent glomerular filtration rate tracer agent relmapirazin (MB-102).

The fluorescent compound relmapirazin has been rationally designed for use in point-of-care measurement of glomerular filtration rate (GFR), with attributes including negligible protein binding, negligible metabolites in vivo, negligible tubular secretion, and excellent chemical and photo stability. Twenty-four nonclinical assays were performed in accordance with FDA requirements yielding negligible toxicology concerns. Here, a clinical study was performed to validate relmapirazin as a GFR tracer in patients by comparison to iohexol. This was evaluated in 120 adults at three clinical sites with eGFR values ranging from normal to Stage 4 chronic kidney disease. Relmapirazin and iohexol were administered intravenously in consecutive boluses to each subject and serial blood samples obtained over the subsequent 12 hours. Plasma concentrations were measured and the corresponding plasma GFR for each agent was determined using a standard two-compartment pharmacokinetic assessment. Urine from each subject was collected for the entire 12-hour study period to measure the amount of administered dose appearing in the urine. A near perfect linear regression correlation was observed between the GFRs measured by these two tracers (r2=0.99). Bland-Altman analysis confirmed agreement between these two measures of GFR (limits of agreement -7.0 to +5.6 mL/min; mean of -0.7 mL/min). The GFR determined by relmapirazin was independent of GFR stratification by chronic kidney disease stage, and importantly by race. The percent of the administered relmapirazin dose recovered in the urine was greater than or equal to that of iohexol with no reported severe adverse events. Thus, relmapirazin may be used as a GFR tracer agent in humans.

GFR measurement in patients with CKD: Performance and feasibility of simplified iohexol plasma clearance techniques.

Implementing shortened one-compartment iohexol plasma clearance models for GFR measurement is crucial since the gold standard inulin renal clearance technique and the reference two-compartment, 10-hour, 16-samplings iohexol plasma clearance method are clinically unfeasible. Inulin may precipitate anaphylactic shock. Four-hour and 8-hour one-compartment iohexol plasma clearance models with Bröchner-Mortensen correction provide accurate GFR measurements in patients with estimated GFR (eGFR) > or ≤40 mL/min/1.73m2, respectively. We compared the performance of the simplified 5-hour, 4-samplings, two-compartment population pharmacokinetic model (popPK) with the performance of the reference two-compartment 10-hour iohexol method in 16 patients with GFR 15.2 to 56.5 mL/min/1.73 m2. We also compared the performance of shortened (5, 6 and 7-hour) one-compartment models with the performance of the standard 8-hour one-compartment model in 101 patients with eGFR ≤40 mL/min/1.73 m2. The performance of popPK and shortened methods versus reference methods was evaluated by total deviation index (TDI), concordance correlation coefficient (CCC) and coverage probability (CP). TDI <10%, CCC ≥0.9 and CP >90% indicated adequate performance. TDI, CCC and CP of popPK were 11.11%, 0.809 and 54.10%, respectively. All shortened, one-compartment models overestimated the GFR (p <0.0001 for all) as compared to the 8-hour model. TDI, CCC and CP were 7.02%, 0.815, and 75.80% for the 7-hour model, 7.26%, 0.803, and 74.20% for the 6-hour model, and 8.85%, 0.729 and 64.70% for the 5-hour model. The agreement of popPK model was comparable to that obtained with the Chronic-Kidney-Disease-Collaboration-Epidemiology (CKD-Epi) and the Modification-of-Diet-in-Renal-Disease (MDRD) serum-creatinine based equations for GFR estimation. PopPK model is remarkably unreliable for GFR measurement in stage III-IV CKD patients. In patients with eGFR ≤40 mL/min/1.73m2, shortened one-compartment models, in particular the 5-hour model, are less performant than the reference 8-hour model. For accurate GFR measurements, the iohexol plasma clearance should be measured with appropriate protocols. Over-simplified procedures should be avoided.

Monitoring iohexol and its transformation products as evidence of reclaimed water irrigation input to contiguous waterbodies.

Irrigation with reclaimed water alleviates water supply shortages, but excess application often results in impairment of contiguous waterbodies. This project investigated the potential use of iohexol, an iodinated contrast media used in medical imaging, together with its bio- and phototransformation products as unique reconnaissance markers of reclaimed water irrigation intrusion at three golf courses within the state of Florida. Inter-facility iohexol concentrations measured in reclaimed waters ranged over ~2 orders of magnitude while observed intra-facility seasonal differences were ≤1 order of magnitude. A ~50 % reduction in iohexol was observed post-disinfection for reclaimed water facilities utilizing UV light while none was observed with use of chlorine. Iohexol biotransformation products were observed to decline or shift to lower molecular weight compounds when exposed to UV light but not during disinfection using chlorine. Iohexol biotransformation products were observed in most of the samples but were more prevalent in samples collected during the dry season. Much fewer iohexol phototransformation products were observed in chlorinated reclaimed water, and they were only observed in UV light irradiated reclaimed water when the pre-disinfectant iohexol concentration was ≥5000 ng/L or from solar exposure of reclaimed water spiked with 10 µM of iohexol. For the Hillsborough golf course overlaying an aquifer, the groundwater did not contain iohexol or phototransformation products but did contain biotransformation products. It is not known if these biotransformation products are from active or historical intrusion. The additional presence of sucralose in the aquifer suggests that intrusion has occurred within the past 3 years. This study demonstrates three crucial points in attempting to utilize iohexol to denote reclaimed water intrusion from irrigation overapplication: (1) interpretable results are obtained when iohexol concentrations in the reclaimed water employed for irrigation are ≥1000 ng/L, with higher concentrations in the range of ≥5000 ng/L better able to meet analytical sensitivity requirements after further dilution or degradation in the environment; (2) it is beneficial to assess iohexol transformation products in tandem with iohexol monitoring to account for environmental transformations of iohexol during storage and transport to the receiving water of concern; and (3) inclusion of monitoring for sucralose, an artificial sweetener ubiquitous in wastewater sources that is comparatively stable in the environment, can aid in interpretating whether reclaimed water intrusion based on identification of iohexol and transformation products in the receiving water is attributable to historic or ongoing irrigation overapplications.

A physiological model for iohexol plasma clearance supporting diagnostics of kidney function.

BACKGROUND: There are several shortcomings in present methods for estimation of GFR from plasma clearance. The aim of the present study was therefore to develop a physiologically based method for calculation of plasma clearance of iohexol. METHODS: A mechanistic model founded on classical biochemical engineering principles where in- and outgoing molecular flows of iohexol between plasma and surrounding tissues were balanced over time. After intravenous injections of iohexol, plasma samples were taken from the investigated subjects until complete elimination of iohexol. After tuning of the model parameters, the clearance value was calculated from the injected dose and the integral of the iohexol concentrations over the investigated period. RESULTS: The mass balance model was able to predict the time course of iohexol distribution and elimination after parameterization of mass balance and kinetic equations. Four model structures were evaluated, all based on model parameters derived from published data and from internal tests, each complied at varying physiological conditions. Iohexol clearance was assessed through the model and compared with calculations from previously practiced methods. When testing the mass balance model on ten healthy subjects, clearance was estimated accurately. CONCLUSIONS: The physiological and mechanistic character of the mass balance model may suggest that its derived clearance comes closer to actual in vivo conditions than data derived from previously practiced calculation methods. Although here, only verified with the clearance marker iohexol, the mass balance model should be applicable also to other renal clearance markers.

Disinfection byproducts of iopamidol, iohexol, diatrizoate and their distinct acute toxicity on Scenedesmus sp., Daphnia magna and Danio rerio.

The COVID-19 pandemic resulted in increasing the usage of iodinated contrast media (ICM), and thus an increase in the prevalence of ICM-contaminated wastewater. While ICM is generally safe, this has the potential to be problematic because as medical wastewater is treated and disinfected, various ICM-derived disinfection byproducts (DBPs) may be generated and released into the environment. However, little information was available about whether ICM-derived DBPs are toxic to aquatic organisms. In this study, the degradation of three typical ICM (iopamidol, iohexol, diatrizoate) at initial concentration of 10 µM and 100 µM in chlorination and peracetic acid without or with NH4+ was investigated, and the potential acute toxicity of treated disinfected water containing potential ICM-derived DBPs on Daphnia magna, Scenedesmus sp. and Danio rerio was tested. The degradation results suggested that only iopamidol was significantly degraded (level of degradation >98%) by chlorination, and the degradation rate of iohexol and diatrizoate were significantly increased in chlorination with NH4+. All three ICM were not degraded in peracetic acid. The toxicity analysis results indicate that only the disinfected water of iopamidol and iohexol by chlorination with NH4+ were toxic to at least one aquatic organism. These results highlighted that the potential ecological risk of ICM-contained medical wastewater by chlorination with NH4+ should not be neglected, and peracetic acid may be an environment-friendly alternative for the disinfection of wastewater containing ICM.

Evaluation of the accumulation of the iodinated contrast agents diatrizoic acid and iohexol in Dreissena polymorpha mollusks.

Mollusks are very sensitive to aquatic environmental alterations and then, are important bio-indicators for monitoring the contamination of water bodies. Iodinated X-ray contrast media (ICMs) are ubiquitously present in the aquatic environment, primarily due to their high consumption for diagnosis purposes, high injection levels, low biodegradability, and low removal rates by wastewater treatment plants. Although these compounds are assumed to be of low toxicity, aquatic organisms are continuously exposed to these agents, which may result in adverse effects as ICMs can act as iodine source and disrupt the endocrine system. Thus, the evaluation of their environmental risk, especially on aquatic fauna is of great interest. To this end, we first compared the accumulation behavior, based on iodine analysis, of two ICM exhibiting different osmolality, diatrizoic acid and iohexol in Dreissena polymorpha bivalves exposed under laboratory conditions at concentrations of 0, 100, and 1000 µg/L during 4 and 7 days. This study was the first to provide information on iodine concentration in whole soft tissues and several organs in control zebra mussels. Moreover, it showed, after exposure, an increase of iodine content mainly in the digestive glands, followed by gills and gonads, highlighting that ICMs actually enter the organisms. Thus, bioaccumulation of ICMs studies were then performed, by liquid chromatography coupled to tandem mass spectrometry, on entire mollusks and digestive glands of organisms exposed at 0, 10, 100, and 1000 µg/L of both ICMs during 21 days, followed by 4 days of depuration. These first data on ICMs concentrations in zebra mussels, showed a clear accumulation of ICMs in mussels as a function of relative exposure level, as well as a rapid depuration. Osmolality did not seem to have a significant impact on the accumulation level, but a slight difference was observed on the accumulation pattern between both ICMs.

Assessing the skin irritation and sensitizing potential of concentrates of water chlorinated in the presence of iodinated X-ray contrast media.

Chemical disinfection of water provides significant public health benefits. However, disinfectants like chlorine can react with naturally occurring materials in the water to form disinfection byproducts (DBPs). Natural levels of iodine have been reported to be too low in some source waters to account for the levels of iodinated DBPs detected. Iodinated X-ray contrast media (ICM) have been identified as a potential source of iodine. The toxicological impact of ICM present in source water at the time of disinfection has not been fully investigated. Iopamidol, iohexol, iopromide, and diatrizoate are among the ICM most frequently detected in water. In this study, source water containing one of these four ICM was chlorinated; non-chlorinated ICM-containing water samples served as controls. Reactions were conducted at an ICM concentration of 5 µM and a chlorine dose of 100 µM over 72 hr. Water concentrates (20,000-fold) were prepared by XAD-resin/ethyl acetate extraction and DMSO solvent exchange. We used the MatTek® reconstituted human epithelial skin irritation model to evaluate the water concentrates and also assessed the dermal irritation and sensitization potential of these concentrates using the LLNA:BrdU ELISA in BALB/c mice. None of the water concentrates tested (2500X) resulted in a skin irritant response in the MatTek® skin irritation model. Likewise, none of the concentrates (2500X, 1250X, 625X, 312.5X, 156.25X) produced a skin irritation response in mice: erythema was minimal; the maximum increase in ear thickness was less than 25%. Importantly, none of the concentrates produced a positive threshold response for allergic skin sensitization at any concentration tested in the LLNA:BrdU ELISA. We conclude that concentrates of water disinfected in the presence of four different ICM did not cause significant skin irritation or effects consistent with skin sensitization at the concentrations tested.

Volumetric absorptive microsampling as alternative sampling technique for renal function assessment in the paediatric population using iohexol.

The glomerular filtration rate (GFR) is considered the best overall index for the renal function. Currently, one of the most promising exogenous markers for GFR assessment is iohexol. In this study, the suitability of volumetric absorptive microsampling (VAMS) as alternative for the conventional blood sampling and quantification of iohexol in paediatric plasma was assessed. Therefore, a new, fully validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed. Subsequently, the clinical suitability was evaluated in 20 paediatric patients by comparing plasma iohexol concentrations and associated GFR values obtained by the VAMS method with those obtained by conventional blood sampling and quantification of iohexol in plasma. The developed, simple and cost-effective LC-MS/MS-method fulfilled all pre-set validation acceptance criteria. Iohexol could be accurately quantified within a haematocrit range of 20-60% and long-term stability of iohexol in VAMS was demonstrated up to 245 days under different storage temperatures. Both iohexol plasma concentrations (r = 0.98, mean bias: -4.20%) and derived GFR values (r = 0.99; mean bias: 1.31%), obtained by a conventional plasma and the VAMS method, demonstrated good correlation and acceptable bias. The agreement between the two methods was especially good for GFR values higher than 60 mL/min/1.73 m2. Nevertheless, for GFR values <60 mL/min/1.73 m2 the accuracy compared to the plasma method was lower. However, small adjustments to the sampling protocol could probably solve this problem.

Optimization of the isolation procedure and culturing conditions for hepatic stellate cells obtained from mouse.

Liver fibrosis (LF) mortality rate is approximately 2 million per year. Irrespective of the etiology of LF, a key element in its development is the transition of hepatic stellate cells (HSCs) from a quiescent phenotype to a myofibroblast-like cell with the production of fibrotic proteins. It is necessary to define optimal isolation and culturing conditions for good HSCs yield and proper phenotype preservation for studying the activation of HSCs in vitro. In the present study, the optimal conditions of HSC isolation and culture were examined to maintain the HSC's undifferentiated phenotype. HSCs were isolated from Balb/c mice liver using Nycodenz, 8, 9.6, and 11%. The efficiency of the isolation procedure was evaluated by cell counting and purity determination by flow cytometry. Quiescent HSCs were cultured in test media supplemented with different combinations of fetal bovine serum (FBS), glutamine (GLN), vitamin A (vitA), insulin, and glucose. The cells were assessed at days 3 and 7 of culture by evaluating the morphology, proliferation using cell counting kit-8, lipid storage using Oil Red O (ORO) staining, expression of a-smooth muscle actin, collagen I, and lecithin-retinol acyltransferase by qRT-PCR and immunocytochemistry (ICC). The results showed that Nycodenz, at 9.6%, yielded the best purity and quantity of HSCs. Maintenance of HSC undifferentiated phenotype was achieved optimizing culturing conditions (serum-free Dulbecco's Modified Eagle's Medium (DMEM) supplemented with glucose (100 mg/dl), GLN (0.5 mM), vitA (100 µM), and insulin (50 ng/ml)) with a certain degree of proliferation allowing their perpetuation in culture. In conclusion, we have defined optimal conditions for HSCs isolation and culture.

Measured and Estimated Glomerular Filtration Rate in the ICU: A Prospective Study.

OBJECTIVES: To compare estimated glomerular filtration rate using classical static and kinetic equations with measured glomerular filtration rate assessed by plasma iohexol clearance in a mixed population of critical care patients. PATIENTS: Unselected patients older than 18 and admitted to a general ICU. DESIGN: Interventional prospective single center study. INTERVENTION: Measurement of glomerular filtration rate by the plasma clearance of an IV single dose of iohexol and estimation of glomerular filtration rate with creatinine or cystatin C-based standard and kinetic equations as well as urinary creatinine clearance. MEASUREMENTS AND MAIN RESULTS: Sixty-three patients were included with a median age of 66 years old. The median measured glomerular filtration rate was 51 mL/min/1.73 m (interquartile range, 19-85 mL/min/1.73 m). All used equations displayed significant biases, high errors, and poor accuracy when compared with measured glomerular filtration rate, overestimating renal function. The highest accuracy and lowest error were observed with cystatin C-based chronic kidney disease epidemiology collaboration equations. Both modification of diet in renal disease and Cockcroft-Gault equations displayed the lowest performance. Kinetic models did not improve performances, except in patients with unstable creatinine levels. Creatinine- but not cystatin C-based estimations largely derived over ICU stay, which appeared more related to sarcopenia than fluid balance. Finally, estimated glomerular filtration rate misclassified patients according to classical glomerular filtration rate categories in approximately half of the studied cases. CONCLUSIONS: All known estimated glomerular filtration rate equations displayed high biases and unacceptable errors when compared with measured glomerular filtration rate in a mixed ICU population, with the lowest performance related to creatinine-based equations compared with cystatin C. In the ICU, we advocate for caution when using creatinine based estimated glomerular filtration rate equations. Drifting of serum creatinine levels over time should also be taken into consideration when assessing renal function in the ICU.

Quantitation of iohexol, a glomerular filtration marker, in human plasma by LC-MS/MS.

We developed a high-performance liquid chromatography mass spectrometry method for quantitating iohexol in 50 µL human plasma. After acetonitrile protein precipitation, chromatographic separation was achieved with a Shodex Asahipak NH2P-50 2D (5 µm, 2 × 150 mm) column and a gradient of 0.1 % formic acid in acetonitrile and 0.1 % formic acid in water over a 10 min run time. Mass spectrometric detection was performed on a Micromass Quatromicro triple-stage bench-top mass spectrometer with electrospray, positive-mode ionization. The assay was linear from 1 to 500 µg/mL for iohexol, proved to be accurate (101.3-102.1 %) and precise (<3.4 %CV), and fulfilled Food and Drug Administration (FDA) criteria for bioanalytical method validation. Recovery from plasma was 53.1-64.2 % and matrix effect was trivial (-3.4 to -1.3 %). Plasma freeze thaw stability (97.4-99.4 %), stability for 5 months at -80 °C (95.5-103.3 %), and stability for 4 h at room temperature (100.6-103.3 %) were all acceptable. This validated assay using a deuterated internal standard will be an important tool in measuring iohexol clearance and determining glomerular filtration rate (GFR) in patients.

Iohexol assay for direct determination of glomerular filtration rate: optimization and development of an HPLC-UV method for measurement in serum and urine.

Determination of glomerular filtration rate (GFR) is considered the best indicator of renal function. Iohexol, a non-ionic contrast agent, is currently considered to be a reference marker since it meets all the requirements of an ideal GFR marker. The aim of our work is to develop and optimize a method for iohexol measurement by HPLC-UV. The results showing the following optimal conditions : a mobile phase with water and 5% of acetonitrile, a C18 analytical column (250 × 4 mm, 5 µm particle size) with a temperature of 40 °C and a flow rate of 1 ml/min. Serum samples are deproteinized by addition of perchloric acid (6%), while urine samples are only diluted. For both matrices, the method is linear (r2 > 0.99) and the recovery is > 98%. For selectivity, no interfering endogenous components at the retention time of iohexol was observed. The results of the matrix effect showed a clinically acceptable variation in most concentration levels except for 100 µg/mL, in urine, where the effect was slightly present. Iohexol stability in urine decreases significantly only after 3 freeze-thaw cycles and after freezing at -80 °C for two months. According to those findings results this method is simple, specific, linear, precise and robust, which allows its application for the direct measurement of the GFR after its analytical validation.

Enhanced specificity due to method specific limits for relative ion intensities in a high-performance liquid chromatography - tandem mass spectrometry method for iohexol in human serum.

Background Accurate assessment of kidney function is needed for a variety of clinical indications and for research. The measurement of the serum clearance of iohexol has emerged as a feasible method to reach this objective. We report the analytical validation and clinical application of a new high-performance liquid chromatography (HPLC) - tandem mass spectrometry (MS/MS) assay to quantify iohexol in human serum. Specificity was enhanced due to the use of method specific acceptance limits for relative ion (RI) intensities. Methods The internal standard ioversol was added to 50 µL serum prior to protein precipitation with methanol. Linear gradient elution was performed on a Waters Oasis® HLB column. Three transitions for both iohexol and ioversol were monitored allowing calculation of RIs. Measurements acquired during method validation were used as a training set to establish stricter acceptance criteria for RIs which were then tested retrospectively on clinical routine measurements (86 measurements) and on mathematically simulated interferences. Results The method was linear between 5.0 µg/mL (lower limit of quantification [LLOQ]) and 100.3 µg/mL iohexol. Intraday and interday imprecision were ≤2.6% and ≤3.2%, respectively. Bias was -1.6% to 1.5%. All validation criteria were met, including selectivity, recovery, extraction efficiency and matrix effects. Retrospectively acceptance limits for RIs could be narrowed to ±4 relative standard deviations of the corresponding RIs in the training set. The new limits resulted in an enhanced sensitivity for the simulated interferences. Conclusions Criteria for validation were met and the assay is now used in our clinical routine diagnostics and in research.

Intestinal barrier dysfunction in liver cirrhosis assessed by iohexol test.

OBJECTIVE: To study gut barrier function in patients with liver cirrhosis (LC) by evaluating the intestinal permeability (IP) and its relationship with the severity and etiology of the disease. PATIENTS AND METHODS: The study included 31 patients with LC and 25 healthy controls. Child-Pugh score was used for evaluation of the LC severity. IP was assessed by the rise in levels of iohexol, which was administered orally (25 mL, 350 mg/mL) 2 h after breakfast. Three and six hours later serum (SIC mg/L) and urine (UIC g/mol) iohexol concentrations were determined by a validated HPLC-UV technique. RESULTS: Patients with LC had significantly higher mean SIC value compared with control group at 3 h (2.05 ± 1.67 vs. 1.25 ± 1.41 mg/L, p=0.021, as well as at 6 h (2.20 ± 2.65 vs. 1.11 ± 1.06 mg/L, p=0.001) after ingestion. No significant difference was found in mean SIC value of patients at 3 and 6 h. 23% of the patients had an increased IP. The mean iohexol urine recovery of patients was similar to that of the controls both at 3 h and at 6 h. Mean SIC values were significantly higher in patients with advanced Child C class than in healthy controls or the subgroup with Child B class, both at 3 h (2.54 ± 1.95 mg/L vs. 1.11 ± 1.06 mg/L, p=0.007) or (2.57 ± 1.85 mg/L vs. 1.35±1.32 mg/L, p=0.005) and at 6 h (2.57 ± 1.85 mg/L vs. 1.25 ± 1.40 mg/L, p=0.002) or 2.54 ± 1.95 mg/L vs. 1.07 ± 0.35 mg/L, p=0.02). Cirrhotic patients with ascites had significantly higher SIC in comparison with the controls, both at 3 h (2.31 ± 1.74 vs. 1.25 ± 1.41 mg/, p=0.009) and at 6 h (2.20 ± 1.87 vs. 1.11 ± 1.06 mg/l, p=0.007). In the subgroup of patients with alcoholic LC, the mean SIC values at 3 and 6 h (2.29 ± 1.80, 2.33 ± 1.85 mg/L, respectively) were significantly higher (p= 0.016, p=0.003) compared to the control group (1.25 ± 1.41, 1.11 ± 1.06 mg/L, respectively). CONCLUSIONS: Increased IP is found in 23% of cirrhotic patients. Permeability alterations are significantly more pronounced in patients with advanced LC with the presence of ascites and in those with alcoholic etiology.

Assessment of the glomerular filtration rate (GFR) in kidney transplant recipients using Bayesian estimation of the iohexol clearance.

Background Plasma iohexol clearance (CLiohexol) is a reference technique for glomerular filtration rate (GFR) determination. In routine practice, CLiohexol is calculated using one of several formulas, which have never been evaluated in kidney transplant recipients. We aimed to model iohexol pharmacokinetics in this population, evaluate the predictive performance of three simplified formulas and evaluate whether a Bayesian algorithm improves CLiohexol estimation. Methods After administration of iohexol, six blood samples were drawn from 151 patients at various time points. The dataset was split into two groups, one to develop the population pharmacokinetic (POPPK) model (n = 103) and the other (n = 48) to estimate the predictive performances of the various GFR estimation methods. GFR reference values (GFRref) in the validation dataset were obtained by non-compartmental pharmacokinetic (PK) analysis. Predictive performances of each method were evaluated in terms of bias (ME), imprecision (root mean square error [RMSE]) and number of predictions out of the ±10% or 15% error interval around the GFRref. Results A two-compartment model best fitted the data. The Bayesian estimator with samples drawn at 30, 120 and 270 min allowed accurate prediction of GFRref (ME = 0.47%, RMSE = 3.42%), as did the Brøchner-Mortensen (BM) formula (ME = - 0.0425%, RMSE = 3.40%). With both methods, none of the CL estimates were outside the ±15% interval and only 2.4% were outside the ±10% for the BM formula (and none for the Bayesian estimator). In patients with GFR ≤30 mL/min/1.73 m2, the BM formula performed very well, while the Bayesian method could not be evaluated in depth due to too small a number of patients with adequate sampling times. Conclusions GFR can be estimated with acceptable accuracy in kidney transplant patients using the BM formula, but also using a Bayesian algorithm.

[Measurement of glomerular filtration rate using a reference method]. / Mesure du débit de filtration glomérulaire par méthode de référence.

Direct measurement methods of glomerular filtration rate (GFR) are considered as the gold standard to assess kidney function. Following the withdrawal of the Proinuline Serb® specialty by the French National Health Surveillance Agency, iohexol remains the most suitable marker to replace inulin as the marker for GFR in France. The assay is performed by high performance liquid chromatography (HPLC) coupled with ultraviolet (UV) detection or by mass spectrometry. Plasma clearance measurement is the protocol of choice: single-sample protocols dominate, but multiple-sample protocols may be more accurate in specific situations to improve accuracy. In some cases, urinary clearance protocols may be proposed. National and international recommendations suggest using a GFR measurement as a confirmatory test in cases where the creatinine-based estimated GFR is inappropriate, ie clinical situations characterized by a significant alteration of muscle mass or volume distribution. The indications retained by the working group were graded according to the level of recommendations. The essential indications are the evaluation of living kidney donor, the monitoring of kidney allograft function at one year post-transplantation, drugs with narrow therapeutic range (anticoagulant, chemotherapy) in patients with inadequate estimation of GFR by creatinine and clinical research.

Usefulness of a saline chaser to reduce contrast material dose in abdominal CT of normal dogs.

Use of a saline chaser has been reported to allow reduction of contrast dose and artifacts during computed tomography (CT) examination in humans. This study assesses the extent of contrast dose by using a saline chaser in abdominal CT scans of normal dogs. Five beagles underwent abdominal CT scans. Three protocols were applied: 600 mg I/kg iohexol without saline chaser (protocol 1), 30% lower dose of iohexol (420 mg I/kg) followed by a 10 mL saline chaser (protocol 2), and 40% lower dose of iohexol (360 mg I/kg) followed by a 10 mL saline chaser (protocol 3). Attenuation values were obtained from aorta, portal vein, and liver parenchyma. The maximum enhancement values (MEVs) in protocol 2 were significantly higher than those in protocols 1 and 3 in the aorta; no difference was seen in the portal vein in all protocols. The liver parenchymal MEVs in protocols 1 and 2 were significantly higher than those obtained in protocol 3. In this study, the use of a saline chaser and a reduced dose of contrast material did not affect vessel enhancement. In conclusion, use of a saline chaser for abdominal CT of dogs is recommended because it allows a 30% reduction of contrast dose without decreasing vascular and hepatic parenchymal enhancement.

Accuracy of determination of the glomerular filtration marker iohexol by European laboratories as monitored by external quality assessment.

Background Glomerular filtration is the most important kidney function. The most accurate glomerular filtration rate (GFR) estimates are based on the clearance of exogenous filtration markers. Of these, iohexol is the only exogenous marker that is included in an external quality assessment (EQA) scheme. The aim of the present study was to evaluate the performance of the European laboratories participating in Equalis' EQA scheme for iohexol. Methods Weighed amounts of iohexol (Omnipaque) were added to plasma samples and distributed to laboratories participating in the EQA scheme for iohexol. All laboratories performed the assays in a blinded fashion. Results The number of participating laboratories varied between 27 and 34 during the study period. Iohexol was determined by HPLC in 77% of the laboratories and by UPLC/MS/MS methods in 15% of the laboratories. The mean interlaboratory coefficient of variation was 4.7% for the HPLC methods and 6.4% for the UPLC/MS/MS methods. The mean bias between calculated and measured iohexol values was -1.3 mg/L (95% confidence interval ±0.3) during the first part of the study period and 0.1 mg/L (±0.3) during the later part. Conclusions The low interlaboratory variation demonstrates that iohexol can be measured reliably by many laboratories and supports the use of iohexol as a GFR marker when there is a need for high quality GFR measurements.

Development and validation of an ultra-high performance liquid chromatography-tandem mass spectrometry method for the simultaneous determination of iohexol, p-aminohippuric acid and creatinine in porcine and broiler chicken plasma.

In order to study the renal function, in terms of glomerular filtration and effective renal plasma flow, in broiler chickens and pigs, an ultra-high performance liquid chromatography-tandem mass spectrometry method for the simultaneous determination of iohexol, p-aminohippuric acid (PAH) and exogenously administered creatinine in plasma was developed and validated. Sample preparation consisted of a deproteinization step using methanol for porcine plasma and an Ostro™ Protein Precipitation & Phospholipid Removal Plate was used for broiler chicken plasma. Chromatographic separation was achieved on a Hypersil Gold aQ column using 0.1% formic acid in water and 0.1% formic acid in methanol as mobile phases. The total run time was limited to 10 min. Matrix-matched calibration curves for iohexol and PAH were prepared and good linearity (r ≥ 0.9973; gof ≤ 6.17%) was achieved over the concentration range tested (0.25-90 µg/mL). Limits of quantification were 0.25 µg/mL for iohexol and PAH. Water was used as surrogate matrix for analysis of creatinine in plasma. This surrogate calibration curve showed good linearity over the concentration range tested (0.25-90 µg/mL) (r ≥ 0.9979; gof ≤ 5.66%). For creatinine, the relative lower limit of quantification was 201.03 ±â€¯49.20% and 60.14 ±â€¯7.64% for chicken and porcine plasma, respectively. The results for within-day and between-day precision and accuracy fell within the specified ranges. This straightforward, cost-effective and rapid method, determining iohexol, PAH and creatinine within one single chromatographic run, has been successfully used for the analysis in porcine and broiler chicken plasma samples in order to determine the renal function of these species.