Abstract
Preanalytical activities, especially those directly connected with blood sample collection
and handling, are the most vulnerable steps throughout the testing process. The receipt
of unsuitable samples is commonplace in laboratory practice and represents a serious
problem, given the reliability of test results can be adversely compromised following
analysis of these specimens. The basic criteria for an appropriate and safe venipuncture
are nearly identical to those used for collecting blood for clinical chemistry and
immunochemistry testing, and entail proper patient identification, use of the correct
technique, as well as appropriate devices and needles. There are, however, some peculiar
aspects, which are deemed to be particularly critical when collecting quality specimens
for clot-based tests, and these require clearer recognition. These include prevention
of prolonged venous stasis, collection of nonhemolyzed specimens, order of draw, and
appropriate filling and mixing of the primary collection tubes. All of these important
preanalytical issues are discussed in this article, and evidence-based suggestions
as well as recommendations on how to obtain a high-quality sample for coagulation
testing are also illustrated. We have also performed an investigation aimed to identify
variation of test results due to underfilling of primary blood tubes, and have identified
a clinically significant bias in test results when tubes are drawn at less than 89%
of total fill for activated partial thromboplastin time, less than 78% for fibrinogen,
and less than 67% for coagulation factor VIII, whereas prothrombin time and activated
protein C resistance remain relatively reliable even in tubes drawn at 67% of the
nominal volume.
Keywords
preanalytical variability - coagulation testing - prothrombin time - activated partial
thromboplastin time - laboratory errors
