2025 Volume 74 Issue 1 Pages 213-218
Activated partial thromboplastin time (APTT) is a test to screen for endogenous and common coagulation factors, although a prolonged APTT is suspected to indicate decreased endogenous and common coagulation factors and the presence of antiphospholipid antibodies. However, centrifugal conditions, anticoagulant medications, heparin contamination, and other factors can affect the measurement results. In order to differentiate between these factors, it is necessary to collect medical history and medication information, and to exclude the influence of heparin in the evaluation. Protamine-supplemented APTT (PS-APTT) is useful for differentiation, but because heparin sensitivity differs among reagents, it is necessary to set the optimal concentration of protamine to be added for each reagent. We investigated the concentration of protamine added to Revohem APTT SLA in unfractionated heparin administered or contaminated specimens with APTT > 34.0 seconds, and found that 123 of 207 (59.4%) had a shortened PS-APTT. In addition, heparin contamination could be distinguished by adding 0.1 mg/mL of protamine sulfate solution to specimens with an APTT of less than 75 seconds and 0.2 mg/mL of protamine sulfate solution to specimens with an APTT of 75 seconds or longer. The PS-APTT could be easily reported except for specimens exceeding the upper limit of the APTT measurement, and it is thought to be possible to report useful results to the clinic by quickly identifying heparin contamination in cases of prolonged APTT.
