• Petra Jilma-Stohlawetz, Susanne Fritsche-Polanz, Peter Quehenberger, Christian Schörgenhofer, Johann Bartko, Robin Ristl, and Bernd Jilma.
• a Department of Laboratory Medicine, Division of Medical and Chemical Laboratory Diagnostics , Medical University of Vienna , Vienna , Austria.
• Scand. J. Clin. Lab. Invest. 2017 Dec 1; 77 (8): 651-657.

Background And AimsThe aim of this study was to assess the circadian variation and the between- and within-subject variation in 10 healthy subjects over a period of 8 weeks by ROTEM®. We further evaluated the influence of elevated body mass index and the effect of low molecular weight heparin and antithrombin on clot formation.MethodsCitrated blood samples were analysed in the NATEM® test system. The clotting time (CT), clot formation time (CFT), maximum clot firmness (MCF) and the maximum lysis (ML) were assessed.ResultsDuplicate measurements showed that 23% of the CT and 31% of the CFT measurements had a coefficient of variation (CV) greater than 10%. The within-subject CV was 16% for the CT and 30% for the CFT. The MCF was fairly constant (6%), whereas ML showed more variation (18%). The between-subject CV was 6% for the CT and 20% for the CFT. Analytical variability was improved by summing up CT and CFT. Compared to morning values, CT, CFT and the sum of CT + CFT were shortened in the afternoon. High body mass index was associated with faster clotting. High concentrations of antithrombin had similar effects on clot formation as 0.2 IU/ml of enoxaparin.ConclusionsTo overcome the influence of diurnal variation, we recommend obtaining blood samples at specified times in the morning. The within-subject variation should be taken into account, when serial measurements of drug effects are required.

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