Paraprotein implicated in hardware failures in nucleic acid testing of blood donors

Analyser blockage due to gel formation by paraproteins leading to invalid results is a rare problem in viral nucleic acid testing (NAT) at New Zealand Blood Service (NZBS) despite many blood samples tested without problems from individuals with known paraproteins. This study aimed to identify common factors in samples causing blockages.

Retrospective data were gathered on blood samples known to have blocked analysers at NZBS testing sites. Patients with plasma cell dyscrasia undergoing haematopoietic stem cell (HSC) harvest formed the comparator arm. These patients were identified from registry data of individuals undergoing autologous stem cell transplantation at Auckland City Hospital between 2013 and 2017.

Four individuals were identified as having blocked analysers between 2010 and 2018. A total of 184 HSC transplant patients were identified, with contemporaneous paraprotein levels available for 177 (96%). Patients with intact immunoglobulin subtypes (134, 73%) were further analysed. Of these, 119 patients (65%) also had total protein and globulin levels available. Mean paraprotein (37.5 g/l), total protein (95.3 g/l), globulin levels (51.5 g/l) and proportion of lambda subtype (75%) were higher in the blocker group compared with non-blocking comparators (4.7 g/l, 66.8 g/l, 27.7 g/l, 36.6% respectively) (P = 0·03, 0·02, 0·007, 0·12). The highest paraprotein and total protein levels from the non-blocking cohort overlapped with the lowest of the blocker group.

High protein levels (paraprotein >20 g/l, total protein >75 g/l) and a trend towards lambda subtype were associated with NAT analyser blockage. The overlap with non-blocking donor samples suggests factors in addition to protein quantity that are also important.