Cardiac troponin T (cTnT) levels are widely used to assess for evidence of myocardial infarction. We studied the effect of freezing and long-term storage on the stability of cTnT in blood samples from 178 patients with end-stage renal failure. The serum was separated and divided into multiple aliquots. Baseline cTnT levels were measured in the unfrozen aliquots. The remaining aliquots were frozen using standard techniques. The aliquots were thawed after 3, 6, 12, or 24 months and cTnT levels measured. There were no significant changes in the mean +/- SEM cTnT levels up to 12 months (0.111 +/- 0.098 microg/L) compared with baseline (0.114 +/- 0.098 microg/L); after 24 months, cTnT levels were significantly lower (0.107 +/- 0.095 microg/L) than baseline ( P = .004). The cTnT assay is a reliable method of measuring the cTnT level in human serum up to 12 months of frozen storage. However, after 24 months, the cTnT level was 0.007 microg/L lower than baseline, potentially causing erroneous interpretations. The clinical significance of the change in the cTnT level after long-term frozen storage is unclear. Further studies, including prospective analysis of patient outcomes, should be helpful.

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Ephedra, a herb reported to suppress appetite and stimulate the sympathetic nervous system as well as cardiac performance, has recently been related to several adverse events, including seizure, stroke, hypertension, myocardial infarction, and sudden death. Here, we describe the case of a 45-year-old woman who died of cardiovascular collapse while taking ephedra. Tissue analysis revealed non-specific degenerative alterations in the myocardium (lipofuscin accumulation, basophilic degeneration and vacuolation of myocytes, as well as myofibrillary loss), associated with myocyte apoptosis, caspase activation, and extensive cleavage of miofibrillary proteins a-actin, a-actinin, and cardiac troponin T. Healthcare professionals are therefore urged to warn their patients about the risk of serious adverse effects, which may follow ephedra intake.

Maximum stability of analytes in chemistry control materials is desired. Stability testing is customarily performed by manufacturers, both prior to distribution of products and during the period following distribution when the products are in the field. Users and evaluators of such materials periodically have reported on experienced stability of various analytes in distributed manufactured products. A wide variety of both testing protocols and definitions of acceptable stability have characterized published reports on the topic. In the present review, we summarize published studies on control material stability in clinical chemistry, review criteria employed to define instability, and present an approach to evaluating stability of analytes involving both statistical and clinical criteria.