In this episode, I’ll discuss how propofol appears to interfere with monitoring heparin using aPTT.
Heparin and propofol have been used together in critically ill patients for decades, but is it possible that there has been a lab interference interaction between these two medications the whole time?
A group of authors recently published in AJHP their findings on propofol-induced interference with activated partial thromboplastin time–based monitoring of therapeutic heparin anticoagulation.
They performed a retrospective observational cohort study looking at 38 ICU patients who received propofol and heparin that was monitored by aPTT. This cohort of patients had 531 aPTTs drawn collectively.
In about one-fifth of the aPTTs results there was documented interference by the lab. 55% of the patients had at least one affected aPTT. 12 of these aPTT values could not be resulted due to the interference, and the remainder required ultracentrifugation prior to reporting, which delays the time to result.
Hemolysis and hyperbilirubinemia were ruled out as causes of the 12 aPTT values that were not able to be resulted.
Because all of the interference occured in about half of the patients, one would think perhaps the dose of propofol was responsible however the authors reported that patients with and without aPTT interference received similar doses of propofol.
The authors concluded:
A potential medication-assay interaction was observed in approximately half of patients who received concomitant propofol and heparin infusions and had aPTT measured for anticoagulation management. Sample ultracentrifugation removes the optical interference in most cases but significantly prolongs aPTT reporting and delays appropriate adjustments to heparin dosing.
Many aPTT tests use optical methods and are susceptible to interference from hemolysis, hyperbilirubinemia, and lipemia. 20% IV lipid emulsion has also been shown to interfere with optical aPTT tests and presumably the lipid vehicle for propofol is responsible for the interference detected by this study.
Many hospitals have moved to anti-Xa based monitoring for heparin infusions which would not be affected however it is surprising that such an interference would be detected between these two medications so long after they began being regularly used together.
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