Assessing the status of European laboratories in evaluating biomarkers for chronic kidney diseases (CKD) and recommendations for improvement: insights from the 2022 EFLM Task Group on CKD survey.

OBJECTIVES: Chronic kidney disease (CKD) is a global health issue, ranking as the third leading cause of death worldwide. CKD diagnosis and management depend on clinical laboratory tests, necessitating consistency for precise patient care. Global harmonization of CKD testing through clinical practice guidelines (CPGs) is recommended. Prior to CPG development, assessing the current CKD testing landscape is crucial. In 2022, the European Federation of Laboratory Medicine (EFLM) conducted an online survey among European laboratories associated with EFLM, evaluating CKD testing practices, including new glomerular filtration rate (GFR) estimation methods. This report summarizes the 2022 survey findings and offers recommendations for improving CKD test standardization. METHODS: An online survey was conducted in November 2022 using a questionnaire hosted on LimeSurvey sent to European laboratories affiliated with the EFLM. The survey results were recorded in Excel files and analysed. RESULTS: The results highlight significant discrepancies among countries in unit expression, methods, cystatin C use, and GFR calculation equations. Additionally, limited attention to pediatric renal biology specifics, varied proteinuria and albuminuria result expressions, and limited awareness of GFR measurement methods through iohexol clearance are noted. CONCLUSIONS: In an effort to enhance the standardization of crucial biomarkers utilized in nephrology for evaluating renal function and diagnosing kidney injuries, the EFLM Task Group on CKD suggests nine practical recommendations tailored for European laboratories. The group is confident that implementing these measures will minimize result expression discrepancies, ultimately leading to enhanced patient care.

Overt and Subclinical Adrenal Insufficiency in Pulmonary Tuberculosis.

BACKGROUND: Tuberculosis of the adrenal glands may cause overt or subclinical adrenal insufficiency. An algorithm-based approach including assessment of paired basal cortisol and plasma adrenocorticotropic hormone (ACTH), short Synacthen, and plasma renin activity assays could be useful to diagnose all forms of adrenal insufficiency. METHODS: This cross-sectional study included consecutive, treatment-naive subjects diagnosed with pulmonary tuberculosis. Tuberculosis severity was classified by radiological criteria. Baseline parameters plus morning (8 am) serum cortisol and paired plasma ACTH were measured in all patients. Synacthen stimulation tests and plasma renin activity assays were performed as required. RESULTS: Eighty-four treatment-naive consecutive cases of pulmonary tuberculosis were evaluated for adrenal insufficiency. Twenty-seven (32.14%) subjects had normal adrenocortical function and 8 (9.5%), 7 (8.3%), 40 (47.6%), and 2 (2.4%) subjects had stage 1, stage 2, stage 3, and stage 4 adrenal insufficiency, respectively. Serum cortisol was negatively correlated with radiological severity (P = .01) and duration of illness (P = .001). Adrenal dysfunction was present in 27.3%, 82.5%, and 80% of those with radiologically minimal, moderately advanced, and far-advanced disease, respectively. Mean cortisol was 19.74 ± 5.52, 17.42 ± 8.53, and 15.71 ± 7.14 (µg/dL) in the 3 groups, respectively (P = .042). Hyponatremia was present in 83.3% of the patients. Serum sodium was negatively correlated with severity but not with the duration of disease. CONCLUSION: The prevalence of overt and subclinical adrenal dysfunction in pulmonary tuberculosis was high and was correlated with disease severity and duration. An algorithmic approach may be useful to detect the same and may have important clinical implications.

New method for calcium on the ADVIA analyzer is free from interference of gadolinium-type contrast agents.

Recently, Siemens Diagnostics released a new calcium assay (CA_2) based on complex formation of calcium with Arsenazo III dye for use on the three automated, random access ADVIA Chemistry analyzers (1650, 2400, and 1200). We evaluated this method for analytical performance as well as potential interference from gadolinium-containing magnetic contrast agents. With Siemens Chemistry serum and urine controls, 2-levels each, the imprecision for the new method was (n=40 each): within-run and total CV of <2.2 and <3.8%, respectively, over all three platforms. The analytical range/linearity of the method (all three systems) was 1-16 mg/dl (serum or plasma) and 1-32 mg/dl (urine). The new method on all three platforms correlated well with a reference (Inductively Coupled Plasma Atomic Emission Spectroscopy) method (n=61, range 4.03-10.30 mg/dl). The ADVIA 1650 CA_2 method also correlated well with the Roche Modular system((R)) Calcium method. The new method showed <10% interference with unconjugated or conjugated bilirubin (50 mg/dl), hemoglobin (1,000 mg/dl), lipids (1,000 mg/dl), and two magnetic resonance contrast agents containing Gadolinium (OptiMARK((R)) 1 mmol/l and Omniscan 1.5 mmol/l). On the contrary, the Roche Calcium method showed significant negative interference with gadolinium-containing contrast agents. We conclude that the ADVIA Ca_2 method can measure serum, plasma, or urine calcium concentrations accurately and is also free from interferences of gadolinium-containing agents.

An improved microalbumin method (microALB_2) with extended analytical measurement range evaluated on the ADVIA chemistry systems.

Quantitative determination of albumin (ALB) in human urine is important to assess kidney functions in a variety of diseases. Recently, Siemens released an improved Microalbumin assay (microALB_2) to measure urinary ALB on the automated, random access ADVIA 1650/1800, ADVIA 2400, and ADVIA 1200 Chemistry Systems. We evaluated analytical performances of this new method. All ADVIA Chemistry Systems use the same microalbumin reagent packs, microALB_2 calibrators, and commercial controls. The within-run and total CVs of the improved method with two-level BioRad Liquichek Urine Chemistry controls (approximately 2 and 9 mg/dl ALB) and a urine pool (approximately 29 mg/dl ALB) on all ADVIA Chemistry systems were <4.1 and <6.1%, respectively (40 replicates per sample). The analytical range/linearity of the method (all ADVIA systems) was from 0.3 mg/dl to theALB concentration in the highest level of calibrator (approximately 38-42 mg/dl). The improved method (microALB_2) on the ADVIA 1650/1800 (y) correlated well with both the Beckman DXC 800 Microalbumin and the old microalbumin method on the ADVIA 1650/1800 analyzers. The improved method showed <10% interference with 16 chemicals from acetaminophen to uric acid that may be present in urine. The improved method has a minimum of 60 days' on-system stability on all systems with the calibration frequencies of (with/without a Reagent Container insert) 20/30 days (ADVIA1200), 50/60 days (ADVIA1650/1800), and 20/60 days (ADVIA2400). No prozone was observed with the method on any platform up to the highest ALB concentration tested in a sample (4,000 mg/dl).

Effect of Asian and Siberian ginseng on serum digoxin measurement by five digoxin immunoassays. Significant variation in digoxin-like immunoreactivity among commercial ginsengs.

Asian and Siberian ginsengs contain glycosides with structural similarities to digoxin. We studied potential interference of ginseng in 5 digoxin immunoassays in 3 Asian (2 liquid extracts, 1 capsule) and 3 Siberian ginseng preparations (1 liquid extract, 2 capsules). With the fluorescence polarization immunoassay (FPIA), we observed apparent digoxin activity in 1 Asian liquid preparation and in the liquid extract and 1 capsule form of Siberian ginseng. In mice fed ginseng, we observed digoxin activities in the serum (Asian, 0.48-0.68 ng/mL [0.6-0.9 nmol/L]; Siberian, 0.20-0.47 ng/mL [0.3-0.6 nmol/L]), indicating that such interferences also occur in vivo. Serum pools prepared from samples from patients receiving digoxin and then supplemented with Asian or Siberian ginseng showed falsely increased digoxin values using the FPIA (e.g., for Asian ginseng, 1.54 ng/mL [2.0 nmol/L] vs control value, 1.10 ng/mL [1.4 nmol/L]) and falsely decreased values using the microparticle enzyme immunoassay (MEIA; 0.73 ng/mL [0.9 nmol/L] vs control value, 1.04 ng/mL [1.3 nmol/L]). Digoxin-like immunoreactive substances (DLISs) showed synergistic effects with ginsengs in interfering with the FPIA and MEIA for digoxin. No interference was observed with 3 other digoxin assays, even in the presence of elevated DLISs.

In vivo digoxin-like immunoreactivity in mice and interference of Chinese medicine Danshen in serum digoxin measurement: elimination of interference by using a chemiluminescent assay.

BACKGROUND: Danshen, a traditional Chinese medicine used in the management of cardiovascular diseases, is available without prescription in the US. Because Danshen is used to treat cardiovascular diseases, we studied the potential interference of Danshen with serum digoxin measurement using various immunoassays. METHODS: Blood was collected 1 day before and then 1 and 2 h after feeding mice with Danshen. The apparent digitoxin activities were measured by the fluorescence polarization immunoassay (FPIA). We also added microliter amounts of Danshen extract to digoxin pools prepared from patients receiving digoxin. The digoxin concentrations were measured using the fluorescence polarization immunoassay (FPIA), microparticle enzyme immunoassay (MEIA) and chemiluminescent assay (CLIA). The observed values were compared with original values. We also fed mice with Danshen. RESULTS: We observed measurable digoxin-like immunoreactivity in sera of mice after feeding with Danshen. We also observed falsely lower digoxin concentrations (negative interference) when MEIA was used for digoxin measurement. However, serum digoxin concentrations were falsely elevated with FPIA. We observed no interference of Danshen in serum digoxin measurement using the CLIA. CONCLUSION: Danshen appears to contain digoxin-like immunoreactivity but does not interfere with serum digoxin measurement when CLIA was used.

Solid-phase extraction for the decontamination of alkali metal, alkaline Earth metal, and ammonium salts from heavy metal ions.

Salicylaldoxime-immobilized silica gel was characterized and used as a potential sorbent for heavy metal ions, viz. Cu(II), Ni(II), Co(II), and Zn(II). The experimental conditions were optimized both in batch and column processes to achieve the maximum efficiency. Kinetic and thermodynamic parameters as well as isotherm constants were evaluated to test the feasibility of the process. The role of various metal ions and different anions were tested in order to monitor the process in case of real samples. The alkali metal, alkaline earth metal, and ammonium salts do not have any effect on the said process. This differential behavior can be effectively used for the decontamination of alkali metal, alkaline earth metal, and ammonium salts from Cu(II), Ni(II), Co(II), and Zn(II) ions via solid phase extraction following AAS measurement. The purification of the salts was confirmed by voltammetric experiment.

Turbidimetric carbamazepine immunoassay on the ADVIA 1650 and 2400 analyzers is free from interference of antihistamine drugs hydroxyzine and cetirizine.

A recent report indicates that hydroxyzine and its active metabolite cetirizine interfere with the particle-enhanced turbidimetric inhibition immunoassay (PENTINA) carbamazepine assay. We studied potential interference of hydroxyzine and cetirizine with the turbidimetric carbamazepine immunoassay on ADVIA 1650 and ADVIA 2400 (Bayer Diagnostics, Tarrytown, NY) analyzers. Aliquots of drug-free serum pools were supplemented with various concentrations of hydroxyzine and cetirizine representing therapeutic, moderate toxic, as well as very toxic concentrations. These samples were assayed by the turbidimetric carbamazepine immunoassay on two analyzers. To study the interference in presence of the analyte, aliquots of a serum pool prepared from patients receiving carbamazepine were further supplemented with various amounts of hydroxyzine and or cetirizine and apparent carbamazepine concentrations were measured again in order to compare with the value of original pool. No apparent carbamazepine concentration was observed when aliquots of drug-free serum were supplemented with hydroxyzine or cetirizine. Moreover, in the carbamazepine pool, the original carbamazepine concentration compared well when aliquots of this serum pool were further supplemented with hydroxyzine or cetirizine. We conclude that the turbidimetric carbamazepine immunoassay is free from interference of hydroxyzine and cetirizine.

False-positive serum tricyclic antidepressant concentrations using fluorescence polarization immunoassay due to the presence of hydroxyzine and cetirizine.

A recent report indicates that hydroxyzine and its active metabolite cetirizine interfere with the PENTINA carbamazepine assay. The potential interference of hydroxyzine and cetirizine with the fluorescence polarization immunoassay (FPIA) and CEDIA assay of carbamazepine as well as with the fluorescence polarization immunoassay of tricyclic antidepressants (TCA) was studied. Aliquots of drug-free serum pools were supplemented with various concentrations of hydroxyzine and cetirizine representing therapeutic, mild to moderate toxic as well as very toxic concentrations. Then apparent carbamazepine and TCA concentrations were measured by immunoassays. Although no interference of hydroxyzine and cetirizine was observed with carbamazepine assays (FPIA and CEDIA), significant apparent TCA concentrations were observed when aliquots of drug-free serum were supplemented with hydroxyzine or cetirizine. Mathematical formula was devised to predict hydroxyzine and/or cetirizine concentration in serum based on observed apparent TCA levels. Hydroxyzine and cetirizine also falsely increased total TCA values when aliquots of serum pool prepared from patients receiving TCA were further supplemented with these drugs. In conclusion, hydroxyzine and cetirizine do not interfere with the FPIA and CEDIA carbamazepine assays but interfere with the measurement of total TCA using the FPIA.

Interference of Asian, American, and Indian (Ashwagandha) ginsengs in serum digoxin measurements by a fluorescence polarization immunoassay can be minimized by using a new enzyme-linked chemiluminescent immunosorbent or turbidimetric assay.

CONTEXT: Ginsengs are widely used by the general population. These herbs interfere with serum digoxin measurement using the fluorescence polarization immunoassay. OBJECTIVE: To assess potential interference of different ginsengs (Asian, American, and Indian, also known as Ashwagandha) in vitro and in vivo in a mouse model by using a new enzyme-linked chemiluminescent immunosorbent digoxin assay and an existing turbidimetric assay. Comparisons were made with the fluorescence polarization immunoassay. DESIGN: Aliquots of drug-free serum pools were supplemented with ginseng and apparent digoxin concentrations were measured using enzyme-linked chemiluminescent immunosorbent digoxin assay, turbidimetric assay, and fluorescence polarization immunoassay digoxin assays. Mice were fed with different ginseng preparations and apparent digoxin concentrations were measured 1 and 3 hours later. In a separate experiment, aliquots of serum digoxin pools were further supplemented with ginsengs and the serum digoxin concentrations were measured again. RESULTS: A significant apparent digoxin concentration was observed both in vitro and in vivo using the fluorescence polarization immunoassay, but no apparent digoxin concentration was observed using enzyme-linked chemiluminescent immunosorbent digoxin assay and turbidimetric assay. No interference was observed with enzyme-linked chemiluminescent immunosorbent digoxin assay and turbidimetric assay when digoxin serum pools were further supplemented with various ginsengs. CONCLUSIONS: It was concluded that both enzyme-linked chemiluminescent immunosorbent and turbidimetric digoxin assays are free from ginseng interferences.

A new enzyme-linked chemiluminescent immunosorbent digoxin assay is virtually free from interference of spironolactone, potassium canrenoate, and their common metabolite canrenone.

Spironolactone and potassium canrenoate (aldosterone antagonist diuretics) are sometimes used in conjunction with digoxin for patient management. Spironolactone, potassium canrenoate, and their common metabolite canrenone interfere with serum digoxin measurement using various immunoassays. Recently a new enzyme-linked chemiluminescent immunosorbent digoxin assay (ECLIA-Digoxin) became commercially available for application on the ADVIA IMS 800i modular system (Bayer HealthCare, Tarrytown, NY). We investigated the potential interference of spironolactone and related compounds in this assay by comparing the results with the fluorescence polarization immunoassay (FPIA), which is known to have significant cross-reactivity with these compounds as well as a turbidimetric assay for digoxin with no known cross-reactivity with spironolactone and related compounds. Aliquots of drug free serum were supplemented with therapeutic and above therapeutic concentrations of spironolactone, canrenone, and potassium canrenoate, and apparent digoxin concentrations were measured. No apparent digoxin concentration was observed using the ECLIA-Digoxin or turbidimetric assay. When serum pools prepared from patients receiving digoxin were further supplemented with these compounds, we observed no significant change in digoxin concentrations in the presence of these compounds with the ECLIA-Digoxin. We conclude that this assay is virtually free from interferences from spironolactone, potassium canrenoate and their common metabolite canrenone.

False-positive serum tricyclic antidepressant concentrations using fluorescence polarization immunoassay due to the presence of hydroxyzine and cetirizine.

A recent report indicates that hydroxyzine and its active metabolite cetirizine interfere with the PENTINA carbamazepine assay. The potential interference of hydroxyzine and cetirizine with the fluorescence polarization immunoassay (FPIA) and CEDIA assay of carbamazepine as well as with the fluorescence polarization immunoassay of tricyclic antidepressants (TCA) was studied. Aliquots of drug-free serum pools were supplemented with various concentrations of hydroxyzine and cetirizine representing therapeutic, mild to moderate toxic as well as very toxic concentrations. Then apparent carbamazepine and TCA concentrations were measured by immunoassays. Although no interference of hydroxyzine and cetirizine was observed with carbamazepine assays (FPIA and CEDIA), significant apparent TCA concentrations were observed when aliquots of drug-free serum were supplemented with hydroxyzine or cetirizine. Mathematical formula was devised to predict hydroxyzine and/or cetirizine concentration in serum based on observed apparent TCA levels. Hydroxyzine and cetirizine also falsely increased total TCA values when aliquots of serum pool prepared from patients receiving TCA were further supplemented with these drugs. In conclusion, hydroxyzine and cetirizine do not interfere with the FPIA and CEDIA carbamazepine assays but interfere with the measurement of total TCA using the FPIA.

The new enzyme-linked immunosorbent digoxin assay on the ADVIA Integrated Modular System is virtually free from oleander interference.

Despite known toxicity of oleander, this product is used in herbal preparations. Oleander interferes with various digoxin immunoassays. It is possible that a person taking digoxin also may take oleander-containing herbal products, and digoxin immunoassays interfering with oleander cannot be used for therapeutic monitoring of digoxin. Recently, Bayer Diagnostics introduced a new enzyme-linked chemiluminescent immunosorbent digoxin assay for application on the ADVIA IMS System (ECLIA-digoxin). We studied potential interference of oleander with this new digoxin assay and found that this assay is virtually free from oleander interference. When aliquots of drug-free serum pools were supplemented with ethyl alcohol extract of oleander leaf or pure oleandrin standard, we observed significant apparent digoxin concentration when measured by the fluorescence polarization immunoassay (FPIA) but minimal digoxin-like immunoreactivity using the ECLIA digoxin assay. Because cross-reactivity should be studied in the presence of primary analyte, we prepared 2 serum pools using sera from patients receiving digoxin. Then aliquots of first digoxin pool were supplemented with oleandrin standard and aliquots of second digoxin pool with oleander extract. We observed significant increases in apparent digoxin concentration in the presence of both oleandrin and oleander extract using the FPIA. However, we observed no statistically significant change in digoxin concentration when ECLIA digoxin assay was used, indicating that this assay is virtually free from oleander interference.

New enzyme-linked chemiluminescent immunosorbent digoxin assay is free from interference of Chinese medicine DanShen.

DanShen is a traditional Chinese medicine indicated for cardiovascular diseases. The potential interference of DanShen with serum digoxin measurement was investigated using a new enzyme-linked chemiluminescent immunosorbent (ECLIA) digoxin assay. Aliquots of drug-free serum were supplemented with ethyl acetate extract of DanShen (4 different brands studied), and apparent digoxin concentrations were measured by the ECLIA as well as fluorescence polarization immunoassay (FPIA) and a turbidimetric assay for comparison. Mice were also fed 4 DanShen preparations and apparent digoxin concentrations were subsequently measured. In another experiment, serum pools containing digoxin were further supplemented with DanShen extracts and digoxin concentrations were measured again by all 3 assays. No apparent digoxin concentration was observed when aliquots of drug-free serum pools were supplemented with DanShen and digoxin concentrations were measured by the ECLIA or the turbidimetric assay. In contrast, significant apparent digoxin concentrations were observed using FPIA, and the highest apparent digoxin concentration was observed with brand 4 of DanShen extract. Similarly, when mice were fed with this herb, significant apparent digoxin concentrations were also observed using FPIA, but neither ECLIA nor turbidimetric assay showed any apparent digoxin concentration. When aliquots of digoxin pool were further supplemented with various DanShen extract, the apparent digoxin concentrations were significantly increased when FPIA was used. In contrast, digoxin concentrations in the presence of DanShen extract compared well with the digoxin concentration of the original pool when ECLIA or turbidimetric assay was used. We conclude that DanShen does not interfere with serum digoxin measurement using a more recently released ECLIA digoxin assay.

Analytic performance evaluation of a new turbidimetric immunoassay for carbamazepine on the ADVIA 1650 analyzer: effect of carbamazepine 10,11-epoxide.

Carbamazepine, an anticonvulsant, requires therapeutic drug monitoring. Recently Bayer HealthCare, Diagnostics Division released a turbidimetric immunoassay of carbamazepine on the ADVIA 1650 analyzer. We evaluated the analytic performance of this assay by comparing values obtained with this new assay in sera of 54 patients receiving carbamazepine with the values obtained by using a widely used fluorescence polarization immunoassay (FPIA) and a chemiluminescent immunoassay (CLIA). The new turbidimetric immunoassay for carbamazepine showed excellent precision. The low control showed a total CV of 4.9% (mean 2.86, SD 0.14 microg/mL), the medium control demonstrated a total CV of 3.5% (mean 7.79, SD 0.27 microg/mL), and the high control showed a total CV of 4.8% (mean 16.15, SD 0.78 microg/mL). The assay was linear up to a carbamazepine concentration of 20 microg/mL. The assay showed excellent dilution recovery and recovery of samples supplemented with carbamazepine (mean recovery 102.2%). We observed an excellent correlation between the values obtained by the FPIA (x-axis) assay and the new turbidimetric (y-axis) assay (y = 0.96 x - 0.46, r = 0.99, n = 54). We also observed excellent correlation between the values obtained by the CLIA (x-axis) and the turbidimetric (y-axis) assay (y = 1.10 x -0.32, r = 0.99, n = 54). However, the slope of 1.10 was higher than the slope of 0.96 observed with the regression equation obtained by using values obtained by the FPIA and the turbidimetric assay. The positive bias obtained with the new turbidimetric assay compared with the CLIA assay resulted from lower cross reactivity of carbamazepine 10,11-epoxide, the active metabolite of carbamazepine, with CLIA. On the other hand, the cross reactivity of the metabolite is similar between the new turbidimetric assay and the FPIA assay. We conclude that the new turbidimetric assay can be used for routine monitoring of carbamazepine in clinical laboratories.

Analytical performance evaluation of a new turbidimetric immunoassay for valproic acid on the ADVIA 1650 analyzer: effect of gross hemolysis and high bilirubin.

Valproic acid is an anticonvulsant that requires careful therapeutic drug monitoring. Valproic acid is also used in psychiatric patients. Bayer Diagnostics (Tarrytown, NY) recently marketed a turbidimetric immunoassay for monitoring valproic acid concentrations in serum or plasma using the ADVIA 1650 analyzer. We evaluated the performance of this new assay by comparing it with a widely used fluorescence polarization immunoassay (FPIA) on the AxSYM analyzer (Abbott Laboratories, Abbott Park, IL). The total coefficient of variation (CV) for the low control of this new assay was 6.8% (mean = 30.7, SD = 2.1 microg/mL, n = 44) while the corresponding CVs for the medium and high controls were 3.3% (mean = 81.0, SD = 2.7 microg/mL, n = 44) and 5.9% (mean = 142.9, SD = 8.4 microg/mL, n = 44), respectively. The assay is linear up to a serum valproic acid concentration of 170 microg/mL, and the detection limit is 4.4 microg/mL. We observed an excellent correlation between the FPIA of valproic acid and the turbidimetric assay using specimens from 52 different patients who were receiving valproic acid. Using the valproic acid concentrations obtained by the FPIA as the x-axis, and the corresponding valproic acid concentrations obtained by the turbidimetric assay as the y-axis, we developed the following regression equation: y = 1.03 x+1.55 (r = 0.98). With this new assay, high concentrations of bilirubin (unconjugated 30 mg/dL and conjugated 30 mg/dL) and gross hemolysis (4+, hemoglobin: 1,500 mg/dL) have no effect on measurements of valproic acid concentration. We conclude that the new turbidimetric assay for valproic acid can be used for routine therapeutic drug monitoring of valproic acid in clinical laboratories.

New enzyme-linked immunosorbent digoxin assay on the ADVIA IMS 800i system is virtually free from interference of endogenous digoxin-like immunoreactive factors.

Endogenous digoxin-like immunoreactive factors (DLIF) may crossreact with antidigoxin antibody and falsely elevate immunoassay results. Recently, a new enzyme-linked immunosorbent chemiluminescent assay for digoxin has been available for use on the ADVIA IMS (Integrated Modular System) 800i analyzer (Bayer Diagnostics). We studied potential interference of DLIF with this new digoxin assay. We analyzed 30 serum specimens from patients who have pathologic conditions that may increase serum DLIF concentrations. These patients were never exposed to digoxin or other agents that may lead to a measurable digoxin concentration. We also analyzed 10 specimens from neonates, 10 cord blood specimens, and 10 amniotic fluid specimens. Apparent digoxin concentrations were measured using the new enzyme-linked immunosorbent digoxin assay (IMS-Digoxin), a fluorescence polarization immunoassay (FPIA), and also a chemiluminescent immunoassay (CLIA, run on ACS:180(R) system from Bayer Diagnostics). We observed measurable apparent digoxin levels with the FPIA in 4 uremic patients (range 0.21-0.36 ng/mL, digoxin equivalent), 7 patients with liver disease (range 0.21-0.72 ng/mL), and 3 patients in the third trimester of pregnancy (0.22-0.66 ng/mL). We also observed measurable DLIF concentrations with the FPIA in 2 neonates (0.22 and 0.36 ng/mL), 5 cord blood specimens (range 0.21-1.18 ng/mL), and 5 amniotic fluid specimens (0.21-0.50 ng/mL). None of these DLIF-positive specimens showed any measurable digoxin concentration using the IMS-Digoxin or the CLIA assay. When serum specimens containing elevated concentrations of DLIF but no digoxin (as measured by FPIA) were supplemented with known concentrations of digoxin, we observed falsely elevated digoxin concentrations, as expected, only by the FPIA. In contrast, we observed a good agreement between the target and observed concentrations when the new IMS-Digoxin or the CLIA assay was used. We conclude that the IMS-Digoxin assay is free from interference of DLIF.

Analytic performance evaluation of a new turbidimetric immunoassay for phenytoin on the ADVIA 1650 analyzer: effect of phenytoin metabolite and analogue.

Phenytoin is an anticonvulsant that requires therapeutic drug monitoring. Recently, Bayer HealthCare, Diagnostics Division released a turbidimetric immunoassay of phenytoin on the ADVIA 1650 analyzer. We evaluated the analytic performance of this assay by comparing values obtained in 52 patients receiving Phenytoin using this new assay with the values obtained by using a widely used fluorescence polarization immunoassay (FPIA). The new turbidimetric immunoassay for phenytoin showed the following imprecision with the low, medium, and high controls: total CV of 5.2% (mean 4.81 microg/mL), 3.7% (mean 16.24 microg/mL), and 4.1% (mean 22.65 microg/mL), respectively. The detection limit of the assay was 0.79 microg/mL, and the assay was linear up to a phenytoin concentration of 46.1 microg/mL. The assay showed excellent dilution recovery and recovery of spiked samples (mean recovery 101.4% and 94.4%, respectively). We observed an excellent correlation between the values obtained by the FPIA (x-axis) assay and the new turbidimetric (y-axis) assay (y=1.06 x-0.61, r=0.98, n=52). We also determined the cross-reactivity of 5-(p-hydroxyphenyl)-5-phenylhydantoin (HPPH), a major metabolite of phenytoin, and of oxaprozine, an analogue with a similar chemical structure to phenytoin, in both phenytoin assays. Both assays showed almost no cross-reactivity to oxaprozine and only small (5%-8%) cross-reactivity to HPPH. We also found that the turbidimetric assay was free from interference at least up to 1200 mg/dL of hemolysis, 30 mg/dL of free bilirubin, 34.5 mg/dL of conjugated bilirubin, and 750 mg/dL of triglyceride (Intralipid). When a drug-free serum was followed by a serum sample containing 38.5 microg/mL of phenytoin, no sample probe carryover effect was observed. We conclude that the new turbidimetric assay can be used for routine monitoring of phenytoin in clinical laboratories.