Performance of direct estradiol immunoassays with human male serum samples.

BACKGROUND: Steroid immunoassays originally required solvent extraction, chromatography, and structurally authentic tracers to avoid interference from steroid cross-reactivity and matrix effects. The demand for steroid assays has driven assay simplification, bypassing this triplet of validity criteria to allow use of unextracted serum, which has introduced bias and nonspecificity at low steroid concentrations. We aimed to evaluate the performance of commercial direct estradiol (E2) immunoassays relative to the reference method of LC-MS and compared serum E2 measurements from each assay with biomarkers of estrogen action. METHODS: We measured serum E2 in duplicate using 5 commercial direct immunoassays and LC-MS in a nested cohort of 101 healthy, asymptomatic men >40 years old from the Healthy Man Study. For each immunoassay, we evaluated the detectability and distribution of serum E2 measurements, CV, and bias (relative to LC-MS) by Passing-Bablok regression and deviance plots. RESULTS: Three assays detected E2 in all samples, whereas E2 was detected in only 53% and 72% of samples by 2 other assays. All 5 assays had positive biases, ranging from 6% to 74%, throughout their ranges. CVs were lower with 4 immunoassays than with LC-MS. LC-MS, but none of the direct immunoassays, correlated with serum testosterone and sex steroid-binding globulin. CONCLUSIONS: The positive bias of direct E2 immunoassays throughout their working range reflects the nonspecific effects of steroid cross-reactivity and/or matrix interference arising from the violation of the triplet validity criteria for steroid immunoassay.

Assessing hypogonadism in men--how helpful are current testosterone assays?

In recent years, hormone therapy (HT) with testosterone has gained increasing prominence and popularity in aging men. It has a demonstrated ability to decrease fat mass and increase lean body mass in men with initial 'low' testosterone levels. The Australian Pharmaceutical Benefits Scheme (PBS) only allows subsidisation of male HT if two morning testosterone values are <8.0 nmol/L (or 8-15 nmol/L with elevated luteinising hormone [LH]). The scientific basis of this 'cut off' for testosterone replacement is unclear but it is close to the lower limit of normal for some laboratories. There is well documented diurnal variation (and even seasonal variation) of testosterone. However, the PBS requirements avoid such diurnal variation by requiring two morning blood samples. The underlying assumption is that all laboratories obtain similar results.

Point-of-care testing of blood glucose in the neonatal unit using the AVL Omni 9 analyser.

BACKGROUND: Blood glucose measurements in newborns at risk of hypoglycaemia are an essential part of their medical management. Blood glucose measurements obtained by point-of-care testing using an AVL Omni 9 blood gas and metabolite analyser were compared with those obtained in the central laboratory using a Dade Dimension RXL analyser. METHODS: Blood glucose was measured at the point of care by nursing staff using an AVL Omni 9 blood gas and metabolite analyser and compared to results obtained in the central laboratory using a DADE Dimension RXL analyser. In total, 123 samples were taken from 114 babies admitted to the neonatal unit. RESULTS: The limits of agreement between the AVL Omni 9 and the central laboratory were 0.0 +/- 0.6 mmol/L for glucose values between 0.5 and 13 mmol/L. Regression analysis showed: AVL Omni 9 glucose = 0.977 x plasma glucose+0.14. There was also a good correlation (r = 0.92) between the AVL Omni 9 and the DADE Dimension RXL analyser for glucose values < 3 mmol/L. The limits of agreement for the AVL Omni 9 when compared with the DADE Dimension RXL analyser were -0.1 +/- 0.5 mmol/L. DISCUSSION: Point-of-care testing of blood glucose using the AVL Omni 9 blood gas and metabolite analyser is a reliable means of measuring blood glucose and has the advantage of providing a fast result using small volumes of blood.