Biological Variation of Hemostasis Variables in Thrombosis and Bleeding: Consequences for Performance Specifications

BACKGROUND

Levels of hemostasis factors vary between and within individuals as a result of genetic and environmental factors and analytical variation of the assays. The current state of the art for defining analytical precision requirements for analytical testing is based on this between- and within-individual (biological) variation. However, information on biological variation in hemostasis variables is still limited.

The aim of this study was to determine the biological variation of coagulation variables involved in thrombosis and bleeding to provide a recommendation for performance specifications and to assess whether hemostasis assays fulfill the recommendation.

METHODS

We performed a longitudinal study by repeated blood sampling (in total 13 times over a 1-year period) in 40 healthy individuals and measured prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen, antithrombin, factor VIII, factor IX, von Willebrand factor (VWF), protein C, and protein S. We evaluated the effect of the biological variation on parameters of analytical variation and propose required performance specifications.

RESULTS

Biological variation was highly different for various hemostasis variables: the within-subject variation ranged from 2.6% (PT) to 25.6% [VWF collagen binding (CB) activity], the between-subject variation varied from 4.1% (PT) to 31.2% (VWF:ristocetin cofactor acitivity), and the assay variation from 1.3% (PT) to 12.9% (VWF:CB).

CONCLUSIONS

With the reagents and analyzers used in this study, most of the hemostasis tests variables fulfill the current quality criteria for diagnosis and monitoring of routine hemostasis assays.

The oral glucose tolerance test: an objective method of interpretation

Oral glucose tolerance test results from a positively-skewed, unimodal distribution were analyzed in such a way as to uncover a natural division within the set of results for each time point. The division in results was obtained from a break in the curve formed when plasma glucose concentration was plotted vs the percentile of the population described by those concentrations. The percentile at which the break occurs separated normal from abnormal glucose concentrations objectively. Previously natural divisions between normal and abnormal glucose concentrations had been found only in bimodal distributions from atypical populations such as the Pima Indians and Nauruans of Micronesia. The glucose concentrations at which separations in our unimodal distribution occur compare well with the available data from the atypical populations. According to one measure of reliability, the 3-h time point was more effective than the more commonly utilized 2-h point in distinguishing normal from abnormal plasma glucose concentration.