British Society for Haematology guidelines for the laboratory diagnosis of malaria

Abstract

The range of supplementary tests available for diagnosing malaria has continued to expand. Despite this, carefully examined thick and thin blood films remain an essential part of the process. This guideline updates the previous 2013 British Society for Haematology Guideline for the Laboratory Diagnosis of Malaria. M ETHODOLOGYThis guideline was compiled according to the British Society for Haematology (BSH) process at https://b-s-h.org.uk/media/ 16732/ bsh-guida nce-devel opmen t-proce ss-dec-5-18.pdf. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) nomenclature was used to evaluate levels of evidence and to assess the strength of recommendations, although there are some challenges with applying these to laboratory diagnostic methods. The GRADE criteria can be found at http://www.grade worki nggro up.org. R EV IEW OF TH E M A N USCR IP TReview of the manuscript was performed by the BSH General Haematology Task Force, the BSH Guidelines Committee and the sounding board of BSH. It was also on the members section of the BSH website for comment.

Dry season prevalence of Plasmodium falciparum in asymptomatic Gambian children, with a comparative evaluation of diagnostic methods

“…The median density of asymptomatic infections found here (3.12 parasites/µL, IQR 1.065-19.57) is 6-fold lower than can be detected by the most experienced microscopists (who can detect approx. 5-20 parasites/µL of blood in a thick lm [34], equivalent to 0.0001% parasitaemia) and 100-fold lower than the 500 parasites/µL of blood that can be reliably detected microscopically by routine diagnostic laboratories [35].…”

Malaria, a laboratory view

“…The laboratory gold standard methods for diagnosis and identification of species and parasitemia determination of malaria are thick and thin peripheral blood smears (with higher sensitivity and specificity, respectively). The thin and the thick blood films should be stained with Giemsa stain (at pH 7.2) 4 . The limit of detection by thick smear is near 50 parasites per microlitre 2 .…”

“…When P. falciparum or P. knowlesi is identified, the parasitemia must be determined using the thin blood film, counting the number of parasitized RBC in a minimum of 1000 (ideally 2000) red blood cells (RBC), 4 or in 20 fields with about 250 RBC (about 5000 red cells) 5 . Only RBC with asexual stages should be counted 4 (gametocytes must be excluded, but always reported). If more than one species is observed, only RBC parasitized with P. falciparum or P. knowlesi must be considered 4 .…”

“…Only RBC with asexual stages should be counted 4 (gametocytes must be excluded, but always reported). If more than one species is observed, only RBC parasitized with P. falciparum or P. knowlesi must be considered 4 . Using this formula parasitemia must be reported as percentage of RBC parasitized.…”

“…The World Health Organization (WHO) suggest the use of the number of parasites per μL of blood in relation to the number of white blood cells (if the count is performed in the thick blood film), or in relation to the number of RBC (if the thin blood film is used) 5 . Quantification of parasitemia must be repeated daily until no parasites remain 4 …”