Donor management implications for high-sensitivity detection of low-level malaria parasitemia in blood donor...

Transfusion-transmitted malaria can occur when donors have unrecognized asymptomatic infection with submicroscopic parasitemia, highlighting the need to detect low-level parasitemia in blood donor screening. However, these highly sensitive blood donor testing algorithms may refer donors to clinicians who use diagnostic algorithms with less analytical sensitivity. Here we describe the analytical sensitivity of a Health Canada (HC)/FDA approved blood donor screening test compared to commonly used diagnostic test algorithms.

The Roche cobas® Malaria NAT performance was assessed. A dilution series of known malaria-positive clinical specimens was prepared (Plasmodium falciparum, P. vivax, and P. ovale) (1:10⁴-10⁷). Percent parasitemia (%parasitemia) via microscopy of clinical samples was used to estimate the infected red blood cells (iRBCs/mL) assuming 5 × 10⁹ RBC/mL. Limit of detection (LoD) at 50% and 95% was calculated. LoDs were compared to currently used Canadian diagnostic methods.

Comparison of whole blood and base matrix LoD₉₅ and LoD₅₀ were within 1 log for detection of Plasmodium spp. Overall, Plasmodium spp. LoD₅₀ was 13.3 iRBC/mL and 2.4 × 10^-7% parasitemia while LoD₉₅ was 167.1 iRBC/mL and 2.8 × 10^-6% parasitemia. LoDs were on average >2 logs lower than other diagnostic tests employed in Canada.

Blood operators using highly sensitive donor testing Plasmodium NATs should develop approaches to educate clinicians on characteristics of these tests, as analytical sensitivities may be more sensitive than current diagnostic testing algorithms. Key groups to engage for management of Plasmodium NAT-positive donors include primary care practitioners, infectious diseases physicians, tropical/travel medicine experts, clinical microbiologists, and public health.