The Influence of Free Hemoglobin and Bilirubin on Heparin Monitoring by Activated Partial Thromboplastin Time and Anti-Xa Assay

Abstract

Context.-Elevated free hemoglobin (Hb) and bilirubinemia complicate extracorporeal membrane oxygenation and could affect unfractionated heparin (UH) therapy monitoring by anti-Xa assay and activated partial thromboplastin time (aPTT).Objectives.-To compare in vitro response of anti-Xa and aPTT assays to UH in samples with artificial hyperbilirubinemia and hyperhemoglobinemia and to estimate if this interference is also observed in vivo in pediatric extracorporeal membrane oxygenation.Design.-Measurement of aPTT and anti-Xa activity in plasma spiked with UH and increased concentration of free Hb and/or conjugated bilirubin. All samples with antiXa activity, antithrombin, free Hb, and bilirubin determination and infused dose of UH from inpatients on extracorporeal membrane oxygenation were extracted from the clinical patient database and analyzed.Results.-Each increment of free Hb by 100 mg/dL significantly shortened aPTT, whereas an increment of bilirubin by 6 mg/dL caused significant prolongation of aPTT and stepwise increase of free Hb and/or bilirubin in plasma decreased anti-Xa activity by 0.03 to 0.05 IU/mL. Extracorporeal membrane oxygenation samples with free Hb 50 mg/dL or greater had significantly lower anti-Xa activity compared with normal ones: 0.33 (0.25-0.42) versus 0.4 (0.31-0.48) IU/mL (P ¼ .01), despite the identical UH infusion and similar antithrombin activity. Moderate increase of free Hb by 59 mg/dL was associated with absolute decrease of anti-Xa activity by 0.07 IU/mL.Conclusions.-Activated partial thromboplastin time and anti-Xa assay are affected by elevated level of free Hb and/or bilirubin in the presence of UH, and lower antiXa activity is noted in extracorporeal membrane oxygenation patients with elevated free Hb. Severe hemolysis and/or hyperbilirubinemia could compromise UH monitoring based on these assays.

Association of outcomes and anti‐Xa levels in the treatment of pediatric venous thromboembolism

“…Patients with renal disease may have impaired clearance of enoxaparin and thus different dosing regimens of this medication. Patients with hyperbilirubinemia were excluded since the colormetric anti‐Xa assay can be affected by elevated serum bilirubin . Patients who received a significant portion of their anticoagulation treatment in the inpatient setting were excluded to avoid differences in anti‐Xa monitoring practices in the inpatient and outpatient settings.…”

Interference in the anti‐Xa heparin activity assay due to hemolysis and icterus during pediatric extracorporeal life support

“…A prior study by Kostousov et al reported that hemoglobin and bilirubin added to plasma samples resulted in a concentration dependent underestimation of heparin activity using an anti‐Xa heparin activity assay . At ~0.46 U/mL heparin and 200 mg/dL plasma hemoglobin the assay underestimated the heparin level by ~0.12 U/mL.…”

“…Since these assays are based on spectroscopic measurements of assay absorbance, typically at 405 nm, substances in the plasma sample that absorb at this wavelength may interfere in the assay. The most common interferences are due to hemolysis (plasma hemoglobin) or icterus (plasma bilirubin) . While the mechanism of the false low interference is not known, it has been hypothesized that hemoglobin binding to heparin might result in partial heparin neutralization .…”

Ventilatory and Pharmacotherapeutic Strategies for Management of Adult Patients on Extracorporeal Life Support

“…Each test has its inherent advantages and disadvantages including availability, cost, turnaround time, influence from factors other than the effect of heparin, and laboratory interference, as well as varying amounts of data for the use of these tests in this setting (Table ). Although ACT is commonly used because of its availability, rapid turnaround time, and familiarity in the context of cardiopulmonary bypass, it appears to be the least reliable marker of heparin's effect during ECLS . Thromboelastography, which provides information about multiple aspects of the clotting cascade, may become more routinely applied in the future, especially if data emerge indicating that it can help optimize pump function and bleeding risk.…”

“…Although ACT is commonly used because of its availability, rapid turnaround time, and familiarity in the context of cardiopulmonary bypass, it appears to be the least reliable marker of heparin's effect during ECLS. [58][59][60][61] Thromboelastography, which provides information about multiple aspects of the clotting cascade, may become more routinely applied in the future, especially if data emerge indicating that it can help optimize pump function and bleeding risk.…”