From Anita Elledge, MT (ASCP), blood bank/coagulation supervisor, Sierra Vista Regional Health Center, AZ: Our coagulation testing is done on a Stago Compact instrument. The linear range is 20–200 s for the activated partial thromboplastin time (APTT, PTT). We have a policy that any PTT result <22 s must be redrawn, not just rerun the same sample, because it is said that a low PTT result should not occur and is almost always due to a bad collection. I can’t seem to find any documentation that confirms the < 22 s result being a point for this “recollect.” Can you give me a resource for information or any further help with this?
Hello, Ms. Elledge, and thank you for your question. I posted a similar question, named “Shortened PTT” on March 13, 2013, and attracted a number of responses. In my post I stated that “only technical artifacts shorten the PTT to less than the lower limit of the reference interval. Artifacts could include partial activation of the coagulation cascade through a specimen collection error, specimen chilling, excessive incubation with the initial PTT reagent prior to adding CaCl2 solution, incorrect reagent formulation, or wrong incubation temperature.” The comments I received provided references for a number of circumstances in which a shortened PTT may indicate a thrombotic condition.
Nothing in the March 13 post specifically answers your question, however, as there is not a study that indicates at what point there should be a redraw; however your local policy seems reasonable. Despite the helpful comments from Drs. Emmanuel Favaloro andVadim Kostousov, most shortened PTTs reflect a specimen artifact or preanalytical variable, and warrant a recollect. If the second specimen is again shortened, it may be an indication of increase thrombosis risk.