We have developed an LC-MS/MS assay for serum cortisol analysis that is suitable for routine clinical use and has been in use in our laboratory for 12 months. The availability of this assay will give more reliable results in patients receiving exogenous steroid therapy.
Background: Considerable intermethod bias has been observed between cortisol immunoassays, with some also displaying a gender difference. Cortisol immunoassay performance is affected by serum matrix effects such as changes in steroid binding proteins and presence of interfering steroids which can be altered in various clinical settings. This study investigates cortisol immunoassay bias in pregnancy, renal failure and intensive care patients. Methods: Serum remaining after routine analysis from pregnant patients, patients on the intensive care unit and patients with renal failure were obtained prior to disposal and used to create 20 anonymous samples per group. A male and female serum pool was prepared and spiked with cortisol. Samples were aliquoted and distributed to four hospitals for cortisol analysis by immunoassays from four different manufacturers. Cortisol was also measured by an isotope dilutiongas chromatography-mass spectrometry method for comparison of assay bias. Results: Differences in cortisol immunoassay bias were observed across the different patient groups. A negative bias compared to pooled serum samples was observed for pregnancy serum, whilst a more positive bias was seen in renal failure and intensive care patients. Variation in bias was greatest in renal failure with the Roche E170 the most affected and the Abbott architect the least (interquartile ranges 44% and 14%, respectively). Conclusions: Cortisol immunoassay bias may be affected by gender and differences in serum matrix from patients with various clinical conditions. Users of cortisol assays should be aware of differing matrix effects on their assay and the relevance of these for the interpretation of clinical results.
Background Cardiac troponin levels offer prognostic information for patients with heart failure. Highly sensitive assays detect levels of cTn much lower than the 99th percentile of standard cTn assays. We hypothesize that cardiac troponin (cTn) levels measured by a high sensitivity assay provide better prognostic value compared to cTn levels measured by a standard assay in patients with chronic heart failure. Methods We measured high sensitivity cTnT (hs-cTnT) and standard cTnI levels, as well as aminoterminal pro B-type natriuretic peptide (NT-proBNP) in 504 sequential stable patients with a history of heart failure who underwent elective coronary angiography, without acute coronary syndrome, and with 5-year follow-up of all-cause mortality. Results The median hs-cTnT level was 21.2 [interquartile range 12.3, 40.9] ng/L and 170 subjects died over 5-years. In a head-to-head overall comparison, hs-cTnT provided increased prognostic utility compared to cTnI (area under the curve [AUC] 66.1% and AUC 69.4%, respectively, p=0.03; 9.0% integrated discrimination improvement, p<.001; and 13.6% event-specific reclassification, p<.001), and was independent of NT-proBNP and renal function. Even within the subset of patients where cTn levels by both assays were above the limit of quantification, higher hs-cTnT is associated with a 2-fold increase in 5-year mortality risk after adjusting for traditional risk factors (tertile 1 vs. 3: Hazard ratio [95% confidence interval] 2.0 [1.3-3.2]; p=0.0002). Conclusion Cardiac troponin can be detected by the high sensitivity assay in more patients with chronic heart failure than the standard assay, and may yield independent and better prognostic accuracy for mortality prediction than standard assay.
Background: Testosterone is measured for the investigation of female hyperandrogenism and male hypogonadism. Liquid chromatography-tandem mass spectrometry (tandem MS) is becoming the method of choice but comprehensive reference ranges are lacking. Methods: Testosterone was measured by tandem MS on 90 healthy women, 67 young healthy men and pregnant women (59 first trimester and 60 second trimester). Results: The male, male calculated free, first trimester and second trimester testosterone reference ranges (derived using the antilog of mean + 1.96 SD of log transformed data) were 10.6-31.9, 0.23 -0.63, 0.6-4.9 and 0.9 -4.9 nmol/L, respectively. The female testosterone upper reference range limit, derived non-parametrically from the 97.5th centile, was ,1.7 nmol/L. Conclusions: We have derived tandem MS testosterone reference ranges to support clinical services.
Higher red cell distribution width (RDW) has been associated with poor prognosis in patients with heart failure (HF). RDW is also closely associated with iron deficiency. However, the mechanism underlying this association is unclear. The relationship between left ventricular end-diastolic pressure (LVEDP) and RDW has not been studied, especially in those without HF. We examined the relationship between LVEDP and RDW in 1,084 consecutive stable patients who underwent elective coronary angiography. We observed that 38% had high LVEDP (>16mmHg) and 29% had history of HF. The median RDW was 13.4%, which was higher with increasing LVEDP (p<0.0001) and significantly higher among patients with HF (p<0.0001). Baseline RDW were independently associated with high LVEDP even after multivariable logistic regression analysis (adjusted odds ratio [OR] per unit change: 1.14, 95% CI: 1.0–1.29, p=0.044). Interestingly, result were stronger in non-HF cohort (adjusted OR per unit change: 1.37, 95% CI: 1.13–1.67, p=0.001). In addition, elevated (third versus first tertiles) RDW levels were independently a predictor of high LVEDP and were associated with a 4.8-fold increased 5-year mortality risk (adjusted hazard ratio: 4.11, 95% CI: 2.12–7.96, p<0.0001), even with the addition of B-type natriuretic peptide to the model (adjusted OR for LVEDP: 2.25, 95% CI: 1.0–5.05, p=0.05; adjusted HR for mortality: 3.79, 95% CI: 1.033–13.89, p=0.044, respectively). In conclusion, high RDW levels were observed in patients with or without HF and independently associated with high LVEDP and with mortality.
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