Do Elevated Hematocrits Prolong the PT/aPTT?

Abstract

The Clinical and Laboratory Standards Institute guidelines require special processing of whole blood specimens with hematocrits greater than 55% due to the possibility of spurious prolongation of routine coagulation studies (PT, aPTT). As samples with hematocrits above 60% are rare at our institution, our study seeks to determine the effect of relative citrate excess on routine coagulation studies in samples with hematocrits of 60% to determine whether special processing is necessary. A calculated volume of 3.2% citrate was added to 1 mL aliquots of 40 whole blood samples in citrated tubes from adult patients to simulate a hematocrit of 60%. A dilutional control was created by adding an equivalent volume of saline to a separate 1 mL aliquot. Routine coagulation studies (PT, aPTT) were run on both samples on the STA Compact Analyzer in accordance with manufacturer instructions. While a paired Student's t-test demonstrated a clinically significant change in both PT and aPTT with the addition of citrate (p = 0.0002 for PT and p = 0.0234 for aPTT), clinical management would not have been altered by any observed change. More interestingly, we observed a shortening of 27/40 PTs and 23/40 aPTTs rather than the expected prolongation. Based on our data, no adjustment of citrate volume appears to be necessary in samples with hematocrits less than or equal to 60%.

Falsely prolonged prothrombin time test in a patient with erythrocytosis: a case report

“…As a result, high hematocrit levels are likely to be encountered by clinical laboratories with relative frequency [7]. However, data suggest that routine coagulation tests can be conducted and analyzed with certainty using samples with hematocrits of up to 60% [8]. Similarly, for hematocrit values below 25% (<0.25), there is no requirement to modify the citrate concentration [9].…”

Effect of anticoagulant adjustment on prothrombin time test using two different PT reagents in patients with elevated hematocrit

“…There are several articles in the literature with this recommendation, but most of them are reviews [ 1 , [6] , [7] , [8] , [9] ], with few research-based articles [ 3 , 16 ]. There is a specific recommendation for using citrate-adjusted tubes from CLSI that can be found in NCCLS document H21-A5 [ 6 ].…”

“…In 2013, Austin M et al. [ 16 ] used thromboplastin extracted from rabbit brain to perform PT tests on samples with artificially high Ht, in which a sufficient volume of 3.2% buffered sodium citrate was added to aliquots to simulate a hematocrit of 60% (final citrate/plasma ratio of 1:3.6). The results of this analysis suggested that the PT test from samples with Ht up to 60% may be performed and interpreted with confidence.…”

Change of routine coagulation parameters in plasma samples with different hematocrit values

“…In addition to sampling from the wrong patient or using inappropriate anticoagulant tubes for sample collection, incorrect sample volume, clotted samples, hemolysis, and lipemia, the patient's age, gender, ethnic group, blood group, physical activity level, stress status, circadian and diurnal rhythm and anticoagulant use are also suggested as preanalytical causes affecting coagulation tests [5,6]. Moreover, the hematocrit values of the patient are another pre-analytical factor that might influence test results [5,7].…”