Creatine kinase-MB mass concentration versus creatine kinase-B activity for the detection of acute myocardial infarction in patients with slightly elevated total creatine kinase activity in serum.

OBJECTIVE: The diagnostic value of creatine kinase-MB mass concentration (CK-MB mass) was compared with that of creatine kinase-B (CK-B) activity in patients with suspected acute myocardial infarction (AMI) but with total serum CK activity only slightly above the reference range. DESIGN: One hundred consecutive blood samples with total CK activity between 120 and 360 U l-1 and CK-B activity > or = 9 U l-1 were analysed. Electrophoresis of CK isoenzymes was also performed. SETTING: Patients from all departments of the hospital were included. About half of the patients originated from the coronary care unit. SUBJECTS: The blood samples derived from 49 patients. Thirteen patients had at least one serum sample with total CK activity above 360 U l-1. These and another three patients were omitted from the study. RESULTS: Acute myocardial infarction had been diagnosed clinically (with CK and CK-B methods) in 12 of 33 patients. However, using the CK-MB mass concentration of the reference method, five of these 12 patients did not have myocardial infarction whereas nine patients with small infarctions were undetected. A good correlation was seen between the results from CK-MB mass concentration and CK isoenzyme electrophoresis, but there was a poor correlation between these methods and CK-B activity including the CK-B/CK ratio. A relatively high proportion (24%) of the selected patients had increased levels of macro CK. CONCLUSION: CK-B activity was inaccurate for the detection of probably myocardial infarction in patients with slightly elevated total CK activity. Increased levels of macro CK interfering with the CK-B assay was one explanation for this observation.

Assay of theophylline: in vivo and in vitro evaluation of dry chemistry and immunoassay versus high-performance liquid chromatography.

In the last decade, kits using dry chemistry have been introduced for analysis of theophylline in biological fluids. We investigated the performance of Ames Seralyzer and Kodak Ektachem 700XR. They were compared to an enzyme immunotechnique (Syva EMIT) and high-performance liquid chromatography (HPLC). Mixed sera from theophylline-treated patients at concentrations of 20, 50, and 80 mumol/L were used. We also investigated the performance of the various methods when assaying theophylline concentrations obtained from individual patients treated or intoxicated with theophylline (n = 35 patients). In within-day analysis, the EMIT method deviated +1- + 9%. the Ektachem 700XR method deviated +2- + 8%, and the Seralyzer method deviated at least + 18% compared to HPLC. Within-day variability was low for all 4 methods. A similar pattern was seen during between-day assay. In five intoxicated patients, EMIT, Seralyzer and Ektachem 700XR deviated at least + 10% compared to HPLC. The Ektachem 700XR method deviated +16- + 36% compared to HPLC, when samples of 240 mumol/L and above were analyzed. Our study shows that theophylline assay kits cannot be recommended in drug analytical laboratories unless specific backup methods are available. EMIT showed the best performance compared to HPLC. Ektachem 700XR gave good results at therapeutic drug concentrations, but was not reliable in intoxicated patients or in those with decreased kidney function.