Influence of mechanical hemolysis of blood on two D-dimer immunoassays

Although there is broad information about the influence of spurious hemolysis on several laboratory tests, less is known on the bias produced on D-dimer testing. Four different pools were obtained from primary blood tubes, and each of them was divided into four aliquots. The first nonhemolyzed was centrifuged, the plasma was separated and then tested for hemolysis index and D-dimer. The second (hemolyzed aliquot A), third (hemolyzed aliquot B) and fourth (hemolyzed aliquot C) aliquots were mechanically hemolyzed by aspirating whole blood one, two and three times through a fine needle. The plasma was then separated and tested for hemolysis index and D-dimer. D-dimer was quantified by HemosIL AcuStar D-dimer and HemosIL D-dimer HS for ACL TOP. Undetectable hemolysis was present in aliquot nonhemolyzed (<0.5 g/l), whereas the concentration of cell-free hemoglobin significantly increased from hemolyzed aliquot A (5.5–7.0 g/l hemoglobin) to hemolyzed aliquot B (11.5 and 15.0 g/l hemoglobin) and hemolyzed aliquot C (20–22 g/l hemoglobin). The plasma concentration of D-dimer decreased from aliquots nonhemolyzed to hemolyzed aliquot C, achieving clinical significance fromhemolyzed aliquot A and hemolyzed aliquot B when measured with D-dimer HS for ACL TOP and AcuStar D-dimer, respectively. The decrease with AcuStar D-dimer was −5 ± 3% in hemolyzed aliquot A, −7 ± 3% in hemolyzed aliquot B, and −9 ± 3% in hemolyzed aliquot C, whereas the decrease with D-dimer HS for ACL TOP was −5 ± 3% in hemolyzed aliquot A, −8 ± 3% in hemolyzed aliquot B and −9 ± 3% in hemolyzed aliquot C. The similar trend towards decreasing values observed when measuring D-dimer with chemiluminescent and turbidimetric immmunoassays on four heterogeneous plasma pools suggest that the hemolysis interference is more likely to be biological than analytical. The modest bias observed in samples with frank hemolysis (i.e. cell-free hemoglobin of 11.5 g/l) confirms that both methods are robust against this type of interference, so that test results might be released in the majority of mildly hemolyzed samples.