Coagulation test results can be influenced easily by biological, preanalytical, and analytical factors due to the peculiar sensitivity of the assay methodology and the potentially adverse clinical consequences of spurious test results.

Clinical biochemists at the Ministry of Health Istanbul Research and Training Hospital (Istanbul, Turkey) retrospectively investigated blood samples collected in centralized units of outpatient clinics for prothrombin time (PT) with 24,050 in group I and 24,500 in group II. In group I, the tubes were inverted and left standing in horizontal position for less than 90 minutes at room temperature. In group II, the tubes were left standing on roller mixer for 3-5 minutes with 30 revolutions per minute (rpm).

On arrival at the clinical biochemistry laboratory, clotted samples were rejected according to “rejection criteria” defined in the laboratory procedure. Samples were rejected if before centrifugation, the clot was visible to the naked eye by moving the blood inside the tube. Samples that yield long clotting times were routinely checked for the reaction curve indicating a clot. The ratios of rejected samples of the two groups were compared statistically with chi-square analysis. The rate of rejection decreased significantly from 0.79% in group I to 0.20% in group II, the roller mixer group.

The authors concluded that using a roller mixer improves the reliability of coagulation testing. Such standardization in preanalytical phase may be helpful in preventing laboratory errors and obtaining correct test results in coagulation tests. They suggest that robotic mechanisms sending the tubes away from the roller exactly after one minute should probably be helpful in avoiding platelet activation. The study was published online on October 7, 2011, in the International Journal of Laboratory Hematology.

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Ministry of Health Istanbul Research and Training Hospital