Do elevated hematocrits prolong the PT/aPTT?

Area of Science:

• Clinical Pathology
• Hematology
• Coagulation Science

Background:

• Clinical and Laboratory Standards Institute guidelines recommend special handling for whole blood with hematocrit >55% to prevent spurious coagulation test results.
• High hematocrit samples (>60%) are rare, necessitating investigation into their specific processing needs.

Purpose of the Study:

• To evaluate the effect of citrate excess on routine coagulation studies (PT, aPTT) in simulated high hematocrit (60%) whole blood specimens.
• To determine if current guidelines for special processing are necessary for samples with hematocrit ≤60%.

Main Methods:

• Whole blood samples from adult patients were collected in citrate tubes.
• A simulated hematocrit of 60% was created by adding a calculated volume of 3.2% citrate to 1 mL aliquots.
• A control aliquot received an equivalent volume of saline for dilution comparison.
• Prothrombin time (PT) and activated partial thromboplastin time (aPTT) were measured using the STA Compact Analyzer.

Main Results:

• A statistically significant change in both PT and aPTT was observed with citrate addition (p=0.0002 for PT, p=0.0234 for aPTT).
• However, the observed changes did not alter clinical management.
• Contrary to the expected prolongation, a shortening of PT was seen in 27/40 samples and aPTT in 23/40 samples.

Conclusions:

• Special citrate volume adjustment is not required for whole blood specimens with hematocrit levels of 60% or less.
• Current coagulation testing protocols are adequate for samples within this hematocrit range, simplifying laboratory procedures.