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High HCT and PT, PTT, and D-dimer

From Barbara Robinson, MT (ASCP), Children’s Hospital of New Orleans, If a sample is tested for D-dimer, prothrombin time (PT) and partial thromboplastin time (aPTT, PTT), and the anticoagulant in tube has not been adjusted for high hematocrit (HCT = 60.8%), what tests would be invalid, and how would results be affected?

Hi, Barbara, and thank you for your question, the PT and PTT would be falsely prolonged, as the concentration of anticoagulant (sodium citrate) would be proportionally raised relative to the volume of patient plasma, which is proportionally reduced in polycythemia. The excess anticoagulant concentration suppresses coagulation. Factor assay results would also turn out to be falsely low because of the false prolongation of the PT and PTT.

I’ve not read or heard anything about D-dimer in an elevated HCT specimen, however I will speculate that since the D-dimer assay is an immunoassay, it is unaffected by anticoagulant concentration, and its results should be reliable.

Comments (2)
Screening Assays
Jul 2, 2013 8:15am

recent paper from Seattle suggests that Ht <= 60% would s
recent paper from Seattle suggests that Ht <= 60% would statistically affect PT and APTT but do not affect clinical management

Austin M, Ferrell C, Reyes M. Do elevated hematocrits prolong the PT/aPTT? Clin Lab Sci. 2013 Spring;26(2):89-94.

Feb 21, 2013 9:15pm

Dear George,
I read with interest your comments regarding t

Dear George,
I read with interest your comments regarding the effect of high HCT on PT, APTT and factor assays. Certainly the PT and APTT are prolonged by the excess citrate as a result of a high HCT and this is more noticeable when the coags are abnormal, eg. a polycythaemic patient on oral anticoagulant. I wondered about the effect in factor assays because the plasma is diluted at least 1/5 with buffer in the assay and our first dilution is usually 1/10 which would reduce the citrate concentration by that dilution factor.
We spiked normal plasma with citrate (0.2 ml 109 mM citrate in 1ml PNP) to simulate around a 70% HCT and found that the factor VIII was essentially unchanged at 1/5 or 1/10 dilution in the factor VIII assay. PT was not much affected but APTT (Actin FS) went from 28 s to 53 s.
Thanks to “Jlow” for this insight, it makes sense that the excess citrate effect is neutralized by the dilution that is routinely used for factor assays. This is extremely helpful to our participants. Geo.

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