PB0161 - A case report of falsely elevated D-dimer result: How aware we are of heterophilic antibodies interference in clinical practice?

Background: Heterophilic antibodies (HAs) are known cause of interference in immunoassays. However, reports of HAs interference on D-dimer results are scarce and underestimated.

Aims: To present the case of falsely elevated D-dimer value caused by HAs leading to patient´s psychological stress and unnecessary additional clinical and laboratory investigation.

Methods: A 41-year old man underwent regular laboratory control in private laboratory. Laboratory diagnostics revealed all results within reference ranges, except elevated D-dimer value (1.53 mg/L FEU, Table 1, sample A). Because of pulmonary embolism two years ago, the patient was upset and the same day, due to chest pressure, was admitted to the hospital Emergency Department (ED) where venous thromboembolism and acute coronary syndrome were ruled out by clinical and laboratory diagnostics. There was no indication for emergency admission and the patient was discharged.

Results: Upon admission to the ED, all laboratory results were within reference ranges, including D-dimer (0.17 mg/L FEU, Table 1, sample B). Because of discrepant D-dimer results obtained the same day by tests 1 and 2, measurements were repeated the next day from same plasma sample (B) by both tests and additionally by test 3 (Table 1, sample C). These results strongly suggested an interference as a potential cause of falsely elevated D-dimer obtained by test 1. The interference of rheumatoid factor (RF) was excluded (RF < 20 IU/mL). Sample C was then treated with heterophilic blocking reagent (HBR, Scantibodies Laboratory Inc., USA) and D-dimer measurements were repeated by all three tests (Table 1, sample D) showing all results within reference ranges and confirming that interference of HAs caused false elevated D-dimer result in test 1.

Conclusion(s): Falsely elevated D-dimer value in test 1 prior to the confirmed HAs interference resulted with discomfort for the patient and extensive additional diagnostic and clinical investigations, suggesting the importance of timely recognition interference of HAs.