The precision of duplicate prothrombin time and partial thromboplastin time assays in neonates

An evaluation of duplicate prothrombin time (PT) and activated partial thromboplastin time (PTT) assays was performed in 277 neonatal samples. Performance criteria were analyzed to determine whether single vs duplicate procedures could be utilized reliably without exposing the neonates to the risk of erroneous PT and PTT results. In addition, we evaluated whether this approach might decrease phlebotomy and hence reduce the number of blood transfusions administered. For PT assays, 97.5% (270/277) of the duplicate results were different by 1 second or less. Only 2.5% (7/277) differed by 3 seconds. For PTT duplicates, 75.0% (207/277) of the values were different by 2 seconds or less and 13.0% (36/277) by 2 to 4 seconds. An additional 12.3% (34/277) were discrepant by as many as 4 seconds. The largest discrepancies occurred in specimens with markedly elevated PT and PTT results, indicative of a significant coagulopathy. In addition, heparin neutralization was performed successfully in 22 neonatal blood specimens showing either partial or full correction of PTT values due to heparin specimen contamination. This study indicates that single PT and PTT assays as well as heparin neutralization tests can be accurately performed and may be able to reduce blood donor exposure by as many as one blood transfusion every 2 to 3 days of hospitalization.