Effect of beef ingestion by humans on plasma concentrations of creatinine, urea, and cystatin C.

PURPOSE: The effect of eating meat on serum concentrations of creatinine has varied among previous reports, with some finding no effect and others finding 50-100% increases, which appears related to how the beef is cooked. For other analytes related to kidney function, urea is well known to increase following a protein meal, and the effect of eating meat on cystatin C concentrations has been studied once. METHODS: We had 32 participants eat a measured amount of cooked beef (5-6 or 10-12 oz; 142-170 or 284-340 g) and collected blood for measurements at 1 h before and immediately before eating beef, then at 1, 2, and 4 h after eating the beef. We measured creatinine using both alkaline picrate and enzymatic methods, cystatin C using a nephelometric immunoassay, and urea using an enzymatic method. RESULTS: For creatinine, both the picrate and enzymatic methods showed similar responses, with a peak average increases of 5.9 µmol/L (0.07 mg/dL) and 4.6 µmol/L (0.05 mg/dL), respectively, at 2 h. Cystatin C had a very slightly maximal decrease of -0.037 mg/L at 2 h. Urea had the largest change, increasing by 0.30 and 0.77 mmol/L at 2 and 4 h respectively. CONCLUSIONS: Healthy individuals were found to have minor increases in serum creatinine (~5 µmol/L) following the ingestion of 5/6 or 10/12 oz of fried beef. Cystatin C appears to decrease very slightly in some people after beef ingestion, possibly due either to circadian variation or to a hormonal effect of eating. We conclude that ingesting these amounts of fried beef has a small effect on plasma creatinine concentrations. Although these increases would likely not affect the diagnosis of a kidney impairment in this population or in those with kidney disease, eating meat before collecting blood for creatinine measurement should be avoided.

Serum 25-hydroxyvitamin D concentrations in dogs with osteosarcoma do not differ from those of age- and weight-matched control dogs.

Vitamin D concentrations show an inverse correlation with incidence of certain tumors in people and dogs. Additionally, human osteosarcoma has been associated with dysregulation of vitamin D-dependent pathways. The study objective was to compare serum 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in 20 dogs with osteosarcoma to age- and weight-matched control dogs. We hypothesized that dogs with osteosarcoma would have lower serum 25-hydroxyvitamin D than control dogs. The mean 25-hydroxyvitamin D3 concentrations for dogs with osteosarcoma and matched-controls were 34.95 ng/mL and 33.85 ng/mL, respectively (P = 0.784). Based on these data, 25-hydroxyvitamin D insufficiency might not be important in the pathogenesis of canine osteosarcoma.

The analytical change in plasma creatinine that constitutes a biologic/physiologic change.

PURPOSE: Accurate and precise measurements of creatinine are necessary to evaluate changes in kidney function related to a decreased glomerular filtration rate (GFR). When serial measurements of creatinine are monitored in an individual, it is useful to know what magnitude of an analytical change in creatinine indicates a true physiologic/biologic change in plasma creatinine that might warrant clinical intervention. METHODS: We compared results between three different methods for creatinine using large chemistry analyzers, two based on alkaline picrate (AP1 and AP2), and one based on dry-slide enzymatic conversion (ENZ). On each of three different segments or days of the study spaced 1-2months apart, we selected 10 different plasma samples having creatinine concentrations ranging from about 0.5mg/dL to 4.5mg/dL (44 to 400µmol/L). Each sample was analyzed in triplicate on each of two same-model analyzers at each institution, then from this data we determined the precision of each model of analyzer. The within-instrument precision of each analyzer was evaluated from the differences between the triplicate results on each sample by each analyzer (mean and SD of the differences). The between-instrument precision was evaluated as the differences between results on the same sample (1, 2, 3, etc.) analyzed on different analyzers of the same model (A and B). This between-analyzer precision data was used to determine both the range and mean±2SD of the differences that could be used to indicate that greater changes in creatinine concentrations would represent a biologic change. RESULTS: The within-instrument precision was best for the ENZ method in comparison to the two alkaline picrate rate methods. The between-instrument precision of the 90 consecutive measurements (30 samples×triplicate analyses) between the same-model analyzers were (mean and SD of differences in mg/dL): -0.018 and 0.029 (ENZ); 0.016 and 0.11 (AP1), and -0.058 and 0.071 (AP2). CONCLUSIONS: While all three of the creatinine methods studied had good precision, the ENZ method had the best precision, such that a change of 0.07mg/dL (6µmol/L) in serial creatinine concentrations up to 1.5mg/dL on a patient could indicate a biologic change had occurred. For the alkaline picrate methods, a measured change of creatinine of 0.23mg/dL for AP1 or 0.11mg/dL for AP2 would indicate that a physiologic change in serum/plasma creatinine has occurred. While a definite biologic change may simply represent daily variations, detecting a biologic change in creatinine more rapidly could impact the ability of creatinine to detect early and clinically significant changes in renal function.

Predicting neonatal respiratory morbidity by lamellar body count and gestational age.

AIMS: To develop a predictive model for assessing the risk of developing neonatal respiratory morbidity using lamellar body counts (LBCs) and gestational age (GA) to provide a more patient-specific assessment. METHODS: Retrospective cohort study of patients' ≥32 weeks' gestation who received amniocentesis with LBC analysis over a 9-year period. Respiratory morbidity was defined as respiratory distress syndrome, transient tachypnea of the newborn or oxygen requirement for >24 h. Logistic regression analyses were used to predict the absolute risk and odds of respiratory morbidity as a function of GA and lamellar body count. RESULTS: Two hundred and sixty-seven mother-infant pairs included in the analysis with 32 cases (12.0%) of respiratory morbidity. When compared to those without respiratory morbidity, neonates with respiratory morbidity had amniocentesis performed at an earlier median GA, had lower mean birthweight and had lower median LBC (P<0.01). The GA specific absolute risks and odds ratios for the presence of respiratory morbidity were calculated. The predicted absolute risks of neonatal respiratory morbidity ranged from 38% at 32 weeks to 6% at 40 weeks when LBC were 35,000/µL. CONCLUSION: GA specific predicted risk of neonatal respiratory morbidity using LBC provides a statistical model, which can aid clinicians in individually counseling patients regarding the absolute risk of their neonate developing respiratory morbidity.

A primer on definitive gas and liquid chromatography drug testing: What clinicians need to know.

OBJECTIVE: To describe the differences between mass spectrometry technologies and compare and contrast them with immunoassay techniques of urine drug testing (UDT). Highlight the potential importance of the differences among these technologies for clinicians so as to allow them make decisions in their use in patient care. METHODS: Review of mass spectrometry techniques, including gas chromatography, liquid chromatography, and time-of-flight techniques. RESULTS: The potential clinical implications of these technologies stemming from their scope and accuracy are presented. SIGNIFICANCE: UDT is an important clinical tool, though there are differences in technology and testing processes with important implications for clinical decision making. It is crucial, therefore, that clinicians have an understanding of the technologies behind the tests they order, so that their interpretation and use of results are based on an understanding of the strengths and weaknesses of the technologies used.

Associations between Body Composition, Hormonal and Lifestyle Factors, Bone Turnover, and BMD.

BACKGROUND: The relative importance of body composition, lifestyle factors, bone turnover and hormonal factors in determining bone mineral density (BMD) is unknown. We studied younger postmenopausal women to determine whether modifiable or nonmodifiable risk factors for osteoporosis have stronger associations with BMD. METHODS: In multivariable linear regression models, we tested associations between non-bone body composition measures, self-reported measures of physical activity and dietary intake, urinary N-telopeptide (NTx), sex hormone concentrations, and BMD in 109 postmenopausal women aged 50 to 64 years, adjusting for current hormone therapy use and clinical risk factors for low BMD. Lean mass, fat mass and areal BMD (aBMD) at the lumbar spine, femoral neck, total hip and distal radius were measured using dual energy X-ray absorptiometry. RESULTS: Higher body weight and self-reported nonwhite race were independently associated with higher aBMD at the lumbar spine, femoral neck, total hip and distal radius. Lean and fat mass were not independently associated with aBMD. Older age and higher urinary NTx were independently associated with lower aBMD at the distal radius but not at weight-bearing sites. Sensitivity analyses demonstrated lack of an independent association between total daily protein or calorie intake and BMD. CONCLUSIONS: BMD, weight and race were the most important determinants of aBMD at all sites. Older age and higher bone turnover were independently associated with lower aBMD at the distal radius. In a limited analysis, self-reported physical activity, dietary protein and calorie intake were not associated with aBMD after adjustment for the other variables.

Osteoporosis in men.

Osteoporosis in men causes significant morbidity and mortality. Bone health declines gradually, often insidiously; and in light of the advancing aging population poses a serious public health issue that is not well recognized. Studies of the past decade have expanded our understanding of the events within, as well as the regulation of, bone remodeling and provided better insight into the physiology and pathophysiology specific to the adult male skeleton. The clinical measurement of bone mineral density using dual-energy X-ray absorptiometry remains the gold standard for diagnosis of osteoporosis in males; and fracture risk assessment is now recognized as a preferred approach to guide treatment decisions. Utilizing surrogate end-points such as increasing bone mineral density and decreasing concentrations of bone resorption markers, clinical trials have demonstrated efficacy in pharmacological treatment of osteoporosis in the adult male. Unfortunately, few studies have evaluated the anti-fracture benefits in this population. Measurement of bone turnover markers may be an additional tool to monitor therapeutic responsiveness in addition to the measurement of bone mineral density.

Evaluation of high resolution gel ß(2)-transferrin for detection of cerebrospinal fluid leak.

BACKGROUND: Cerebrospinal fluid (CSF) leaks are potentially life-threatening conditions that can be diagnosed by detection of ß(2)-transferrin using protein electrophoresis. Another less commonly available test is ß-trace protein quantitation using immunoassay. The objectives of this study were to evaluate a new immunofixation-based ß(2)-transferrin test for detection of CSF leaks and to compare it to an existing agarose gel electrophoresis test and ß-trace protein immunoassay. METHODS: For method comparison, 63 consecutive samples from physician-ordered ß(2)-transferrin tests were analyzed using two different electrophoresis methods, agarose gel fractionation followed by acid-violet staining, and high resolution agarose gel electrophoresis followed by ß(2)-transferrin immunofixation. A subset of samples (16/63) were analyzed for ß-trace protein. Results were compared against patient chart data for the presence of a CSF leak. Additional studies were performed to assess the stability, detection limit, and analytical specificity of the ß(2)-transferrin immunofixation test. RESULTS: The ß(2)-transferrin immunofixation test had a sensitivity of 100 % (40/40) and specificity of 71 % (12/17) for detection of CSF leaks. By comparison, the agarose gel test had a sensitivity of 87 % (35/40) and specificity of 94 % (16/17). ß-trace protein had a sensitivity of 100 % (10/10) and specificity of 86 % (5/6). Serum and saliva could be differentiated from CSF by the ß(2)-transferrin immunofixation test based on their migration patterns. However, whole blood samples appeared positive for ß(2)-transferrin at a threshold of ~ 4 g/L hemoglobin. At a cut-off of 3 mg/L, ß-trace protein was increased in 10/10 cases with documented CSF leak and in 1/6 patients without CSF leak. CONCLUSIONS: Both the new immunofixation test for ß(2)-transferrin and the ß-trace protein were effective at detecting CSF leaks. Users of the ß(2)-transferrin immunofixation test should be cautioned against interpreting samples with blood contamination.

An introduction to drug testing: the expanding role of mass spectrometry.

Measurement of drugs and their metabolites in biological fluids is the foundation of both therapeutic drug monitoring (TDM) and toxicology. Though different in their application, each discipline depends upon accurate identification and quantification if the measurements are to be useful. Thousands of methods are described for drug analysis but until recently most have relied upon analytical tools, such as spectrophotometry and immunoassay, that suffer from lack of specificity and sensitivity. The introduction of methods based on mass spectrometry (MS), coupled to gas or liquid chromatography, has revolutionized these areas. The methods are proving to be robust, versatile, and economical. This chapter introduces the reader to the application of MS to TDM and toxicology, the steps that should be considered during implementation, and the processes that should be implemented to assure continued quality.

Unexpected interference of baby wash products with a cannabinoid (THC) immunoassay.

OBJECTIVES: The results of newborn drug screening have far-reaching impact not only in healthcare, but also in the legal domain. Therefore, the accuracy of these results cannot be undervalued. When false positive cannabinoid (THC) screening results for this population were suspected at our institution, a multidisciplinary approach was initiated to evaluate the screening process for any pre-analytical or analytical sources of error or interference. DESIGN AND METHODS: Mixtures of drug-free urine with various commercial products and materials that commonly contact newborns in our nursery were prepared and tested using the immunoassay screening methods in our laboratory. Additional commercial products were similarly tested; and when available, individual surfactants common to the interfering products were also evaluated. RESULTS: Addition of Head-to-Toe Baby Wash to drug-free urine produced a dose dependent measureable response in the THC immunoassay. Addition of other commercially available baby soaps gave similar results, and subsequent testing identified specific chemical surfactants that reacted with the THC immunoassay. CONCLUSION: We have identified commonly used soap and wash products used for newborn and infant care as potential causes of false positive THC screening results. Such results in this population can lead to involvement by social services or false child abuse allegations. Given these consequences, it is important for laboratories and providers to be aware of this potential source for false positive screening results and to consider confirmation before initiating interventions. Most importantly, we demonstrate the need for active involvement in the "total testing process," as sources of error are not confined to the laboratory walls.

Follicle-stimulating hormone is independently associated with lean mass but not BMD in younger postmenopausal women.

PURPOSE: Increased follicle-stimulating hormone (FSH) has been associated with lower bone mineral density (BMD) in animal models and longitudinal studies of women, but a direct effect has not been demonstrated. METHODS: We tested associations between FSH, non-bone body composition measures and BMD in 94 younger (aged 50 to 64 years) postmenopausal women without current use of hormone therapy, adjusting for sex hormone concentrations and clinical risk factors for osteoporosis. Lean mass, fat mass and areal BMD (aBMD) at the spine, femoral neck and total hip were measured using dual energy X-ray absorptiometry (DXA). Volumetric BMD (vBMD) was measured at the distal radius using peripheral quantitative computed tomography (pQCT). RESULTS: FSH was inversely correlated with lean and fat mass, bioavailable estradiol, spine and hip aBMD, and vBMD at the ultradistal radius. In the multivariable analysis, FSH was independently associated with lean mass (ß=-0.099, p=0.005) after adjustment for age, race, years since menopause, bioavailable estradiol, bioavailable testosterone, LH, PTH, SHBG and urine N-telopeptide. FSH showed no statistically significant association with aBMD at any site or pQCT measures at the distal radius in adjusted models. Race was independently associated with aBMD, and race and urine N-telopeptide were independently associated with bone area and vBMD. CONCLUSIONS: After adjustment for hormonal measures and osteoporosis risk factors, higher concentrations of FSH were independently associated with lower lean mass, but not with BMD. Previously reported correlations between FSH and BMD might have been due to indirect associations via lean mass or weight.

Multi-center evaluation of a commercial Kit for tacrolimus determination by LC/MS/MS.

OBJECTIVES: A multi-center evaluation (3 sites) of the LC/MS/MS MassTrak tacrolimus Immunosuppressants Kit (Kit) was undertaken. DESIGN AND METHODS: Ten aspects of the analytical performance of the Kit were investigated based on FDA and CLSI guidelines. RESULTS: The linear analytical range of the procedure was between 0.68 and 31.7ng/mL. Within-run and total imprecision were <6% and <8% (n=240), respectively. Recoveries of tacrolimus added to clinical samples that contained between 5 and 10ng/mL of tacrolimus before addition were 99, 102 and 105% at 5.0, 10 and 20ng/mL, respectively. Comparison of in-house and Kit procedures in samples from liver (n=50-58) or kidney (n=50 or 51) transplant recipients yielded method mean biases between -2.0 and +10.7% at 5 and 15ng/mL. CONCLUSIONS: This evaluation indicates that the Kit is suitable for the monitoring of tacrolimus in kidney and liver transplant recipients.

The evolution of mass spectrometry in the clinical laboratory.

Clinical laboratories around the world are recognizing the power of mass spectrometry. This technique, especially when coupled to gas chromatography or liquid chromatography, is revolutionizing the analysis of many analytes. Unlike many other techniques which measure one analyte at a time, these techniques can measure multiple analytes (>40) at one time. In recent years the scope of testing using these techniques has expanded from toxicological purposes to newborn screening to hormones, proteins, and enzymes. It is not uncommon any more to see mass spectrometry being used in the routine clinical laboratories.