All troponins are not created equal.

Troponin measurement is central to the management and risk stratification of acute coronary syndromes. Decisions are made by categorizing troponin as positive or negative. We sought to evaluate categorical agreement between four troponin assays. Sixty blood samples were analysed by three troponin I assays (Centaur, Architect and point-of-care i-STAT) and one troponin T (TnT) assay (Roche Elecys). The upper reference limit was taken as the lowest value with a coefficient of variation of 10% or less. Continuous agreement between assays was good (Pearson's correlation coefficient 0.871-0.995). Categorical agreement assessed by Cohen's kappa varied from poor (between Architect and Centaur kappa = 0.37, and between TnT and Centaur kappa = 0.48) to good (between Architect and i-STAT kappa = 0.68, and between TnT and i-STAT kappa = 0.68). Percentage of positive results varied almost twofold, from 37% for the Centaur to 72% for the Architect. Comparison of four troponin assays showed up to twofold variations in the proportion of positive results. This implies that either a large proportion of troponin-positive diagnoses are missed by some assays or the assays with higher positivity are generating large numbers of false positives. Clinicians should evaluate troponin results in the clinical context and not base decisions solely on the 'normal range' of their local troponin assay.

Transient expression and mutational analysis of the rotavirus intracellular receptor: the C-terminal methionine residue is essential for ligand binding.

Maturation of rotavirus involves an intracellular membrane budding event in which the single-shelled icosahedral particle interacts with a virus-encoded receptor glycoprotein, NS28, that is located in the rough endoplasmic reticulum membrane. The receptor is a tetramer and is oriented with the C-terminal 131 amino acids on the cytoplasmic side of the membrane (A.R. Bellamy and G.W. Both, Adv. Virus Res. 38:1-48, 1990). We have used the T7-vaccinia virus transient expression system to deliver mutant variants of the NS28 gene to CV1 cells in order to assess the effects of site-specific modifications on receptor function. Three types of mutant proteins have been constructed by altering the extreme C-terminal methionine, cysteine residues within the third hydrophobic domain, and internal residues located within the cytoplasmic portion of the receptor, respectively. Deletion or conservative substitution of the C-terminal methionine completely abolishes receptor activity. Substitution of cysteine residues has no effect on receptor activity or on the ability of the receptor to adopt its native oligomeric state. Internal deletions result only in a reduction in the level of binding. An N-terminally truncated form of the receptor, containing only the cytoplasmic domain, retains full receptor activity and can form membrane-associated tetramers.