BackgroundVitamin D is not only important for bone health but can also affect the development of several non-bone diseases. The definition of vitamin D insufficiency by serum levels of 25-hydroxyvitamin D depends on the clinical outcome but might also be a consequence of analytical methods used for the definition. Although numerous 25-hydroxyvitamin D assays are available, their comparability is uncertain. We therefore aim to investigate the precision, accuracy and clinical consequences of differences in performance between three common commercially available assays.Methodology/Principal FindingsSerum 25-hydroxyvitamin D levels from 204 twins from the Swedish Twin Registry were determined with high-pressure liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (HPLC-APCI-MS), a radioimmunoassay (RIA) and a chemiluminescent immunoassay (CLIA). High inter-assay disagreement was found. Mean 25-hydroxyvitamin D levels were highest for the HPLC-APCI-MS technique (85 nmol/L, 95% CI 81–89), intermediate for RIA (70 nmol/L, 95% CI 66–74) and lowest with CLIA (60 nmol/L, 95% CI 56–64). Using a 50-nmol/L cut-off, 8% of the subjects were insufficient using HPLC-APCI-MS, 22% with RIA and 43% by CLIA. Because of the heritable component of 25-hydroxyvitamin D status, the accuracy of each method could indirectly be assessed by comparison of within-twin pair correlations. The strongest correlation was found for HPLC-APCI-MS (r = 0.7), intermediate for RIA (r = 0.5) and lowest for CLIA (r = 0.4). Regression analyses between the methods revealed a non-uniform variance (p<0.0001) depending on level of 25-hydroxyvitamin D.Conclusions/SignificanceThere are substantial inter-assay differences in performance. The most valid method was HPLC-APCI-MS. Calibration between 25-hydroxyvitamin D assays is intricate.

Background-Risk stratification and the use of specific biomarkers have been proposed for tailoring treatment in patients with non-ST-elevation acute coronary syndrome (NSTE-ACS). We investigated the prognostic importance of highsensitivity troponin T (hs-TnT), N-terminal pro-brain natriuretic peptide (NT-proBNP), and growth differentiation factor-15 (GDF-15) in relation to randomized treatment (ticagrelor versus clopidogrel) and management strategy (with or without revascularization) in the NSTE-ACS subgroup of the Platelet Inhibition and Patient Outcomes (PLATO) trial. Methods and Results-Of 18 624 patients in the PLATO trial, 9946 had an entry diagnosis of NSTE-ACS and baseline blood samples available. During index hospitalization, 5357 were revascularized, and 4589 were managed without revascularization. Hs-TnT, NT-proBNP, and GDF-15 were determined and assessed according to predefined cutoff levels. Median follow-up was 9.1 months. Increasing levels of hs-TnT were associated with increasing risk of cardiovascular death, myocardial infarction, and stroke in medically managed patients (P<0.001), but not in those managed invasively. NT-proBNP and GDF-15 levels were associated with the same events independent of management strategy. Ticagrelor versus clopidogrel reduced the rate of cardiovascular death, myocardial infarction, and stroke in patients with NSTE-ACS and hs-TnT ≥14.0 ng/L in both invasively and noninvasively managed patients; in patients with hs-TnT <14.0 ng/L, there was no difference between ticagrelor and clopidogrel in the noninvasive group Conclusions-Hs-TnT, NT-proBNP, and GDF-15 are predictors of cardiovascular death, myocardial infarction, and stroke in patients with NSTE-ACS managed noninvasively, and NT-proBNP and GDF-15 also in those managed invasively. Elevated hs-TnT predicts substantial benefit of ticagrelor over clopidogrel both in invasively and noninvasively managed patients, but no apparent benefit was seen at normal hs-TnT. Clinical Trial Registration-URL:http://www.clinicaltrials.gov. Unique identifier: NCT00391872. [3][4][5] using the invasive approach only in the case of remaining signs or symptoms of ischemia. 6,7 To select the most appropriate strategy, both clinical risk scores and the use of biomarkers have been advocated. Over the past decades, elevated levels of troponin, [8][9][10] N-terminal probrain natriuretic peptide (NT-proBNP), 11,12 and growth differentiation factor-15 (GDF-15) [13][14][15] have been associated with worse outcome and benefit of an early invasive strategy. Elevated levels of troponin have also been found to identify those with larger benefit from antithrombotic treatment, eg, glycoprotein IIb/IIIa inhibitors, 16 and low-molecular-weight heparins.17 Currently, troponin is the only biomarker recommended to be included among the factors used for decision support in the treatment guidelines. 1,2 Editorial see p 278 Clinical Perspective on p 303The Platelet Inhibition and Patient Outcomes (PLATO) trial recently showed that the oral P2Y 12 -inhibitor tic...

Biomarker measurement on admission is feasible and provides incremental risk stratification in patients with STEMI treated with PPCI, with NT-proBNP and GDF-15 being most valuable due to the association with both CVD and spontaneous MI.

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