Evaluation of the Abbott IMx fluorescence polarization immunoassay and the bio-rad enzyme immunoassay for homocysteine: comparison with high-performance liquid chromatography.

We evaluated the precision, linearity and accuracy of the Abbott IMx and Bio-Rad (Axis) homocysteine assays. Both assays make use of S-adenosyl-homocysteine hydrolase and excess adenosine, to convert homocysteine to S-adenosylhomocysteine (SAH). A monoclonal anti-SAH antibody is then used to quantify SAH. The IMx assay measures the fluorescence polarization of a conjugated SAH analogue for the final analytical step, whereas the Bio-Rad method uses a microplate enzyme immunoassay (EIA) employing an anti-mouse antibody peroxidase conjugate. The Abbott procedure is completely automated whereas the Bio-Rad EIA is performed manually. Between-run coefficient of variation using commercial controls was 2.6% at 7 micromol/L, 2.5% at 13 micromol/L and 1.7% at 24 micromol/L for the Abbott method, and 19.7% at 6.4 micromol/L, 15.9% at 11.0 micromol/L and 14.5% at 23.4 micromol/L for the Bio-Rad method. Both assays correlated well with a high-performance liquid chromatography (HPLC) procedure for homocysteine: Bio-Rad EIA = 1.03HPLC + 1.0 micromol/L, r=0.98, s(y/x)=0.51; Abbott IMx = 1.02HPLC + 0.7 micromol/L, r=0.99, s(y/x) = 0.33. Both methods were linear up to 50 micromol/L homocysteine. The IMx assay had superior precision as well as the technological advantage of being completely automated. Both immunoassays exhibited greatly improved throughput compared with our existing HPLC method.

Laboratory and clinical evaluation of two glucose meters for the neonatal intensive care unit.

OBJECTIVE: To evaluate the analytical and clinical performance of the One Touch II and Advantage glucose meters for use in neonatal specimens. DESIGN AND METHODS: For the laboratory evaluation, a total of 96 umbilical cord whole blood specimens were analyzed on the One Touch II and/or Advantage meters. Samples were centrifuged after analysis on the meters and plasma glucose was determined on the Hitachi 917. For the clinical evaluation, a total of 64 infants had specimens analyzed on each of the meters as well as on the laboratory analyzer. RESULTS: In the laboratory and clinical evaluations, both meters correlated well (r > 0.9, p < 0.001) with the plasma values for the Hitachi 917. However, the mean difference between the Advantage and Hitachi 917 was lower than that of the One Touch II in both the laboratory (-0.23 vs -0.64 mmol/L) and the clinical evaluations (-0.08 vs -0.60 mmol/L). 53.1% of One Touch and 26.6% of Advantage results from the clinical study had a discrepancy of > 0.5 mmol/L from the laboratory value. CONCLUSIONS: For neonatal specimens, glucose meters must have good low end precision, sensitivity and accuracy, In this study, the Advantage meter had fewer discordant results and better correlation with the Hitachi 917. Overall, nursing and laboratory staff preferred the performance and characteristics of the Advantage meter.

Establishing reference intervals for DPC's free testosterone radioimmunoassay.

OBJECTIVE: To establish reference intervals for serum free testosterone for DPC's Free Testosterone assay. METHODS: We used data from healthy subjects and patients to determine reference intervals by parametric and non-parametric methods after partitioning by sex and age. RESULTS: In males, there was a significant decrease in free testosterone concentrations with age. Reference intervals derived from a combination of 2075 "healthy" and patients' results gave similar values by parametric and nonparametric methods. However, the subgroups failed the test for Gaussian distribution. For each decade from 20 years on and > or = 60 years, the intervals based on 2.5th and 97.5th percentiles were: 24.1-94.8, 25.0-89.3, 23.4-81.7, 22.5-80.4, and 21.5-74.3 pmol/L respectively, in females, there was little change with age. The frequency distribution of 1915 patients was positively skewed, and showed a wider range than "healthy." Using square roots of values gave a Gaussian distribution. The central 95% intervals based on 187 "healthy" subjects were: 0.5-8.1 and 0.0-6.4 pmol/L for 20-59 and > or = 60 years, respectively. CONCLUSION: Developing reference intervals for free testosterone was complicated by the need to partition data by gender and age, difficulty in establishing disease in subjects and presence of physiological and other factors which can affect concentration in health and disease.