Interfering antibodies may contribute to elevated D-dimer: a case report

Background Plasma levels of d-dimer are elevated in patients with thromboembolisms. Here we investigated the existence of interfering antibodies as a potential cause for elevated d-dimer levels. Case presentation A 42-year-old white Caucasian woman with a prior history of pulmonary embolism during her first pregnancy (treated with heparin therapy for 6 weeks postnatally) and hypothyroidism had a persistent elevated d-dimer without any clinical or ultrasound-based signs of thromboembolic conditions during her second pregnancy. We obtained informed consent and plasma was obtained from the patient. D-dimer levels were measured using two different assays. We also tested for the presence of rheumatoid factor, performed dilution series, and finally used an antibody depletion strategy. The two d-dimer assays performed similarly. Using our antibody depletion technique, we observed that similar to 1/3 of the increased plasma levels of d-dimer may be attributed to interfering antibodies. Conclusions Our results identify interfering antibodies as a potential contributor to an increased d-dimer in this patient. Our case highlights the potential of heterophilic interference for increased d-dimer and provides a procedure to determine this analytically.