Malaria: Sensitivity and Specificity

Introduction: Malaria is the disease caused by infection with Plasmodium species, predominantly P falciparum (more fulminant course) and P vivax / P ovale (less severe but has a dormant phase in the liver).

Note that some of the diagnostic tests are for malaria in general, while others are specific to one species.

The BinaxNOW is currently the only FDA approved rapid test for malaria (per UpToDate).

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Prevalence

Population / Calculator	Prevalence	Comments / Study / Link
Blood Smears Sent from US Hospitals	11%	Clin Infect Dis. 2009 Sep 15;49(6):908-13. PMID 19686072
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The sensitivity and specificity of findings for Malaria are listed below. See the left navigation bar to change the display.

Pre-Test Probability (Prevalence): %.	Post-Test Probability (Predictive Value): %.	Switch to display mode.
Note that calculating probabilities from more than one** finding is inherently inaccurate because findings are not independent. (For example, using two positive findings that share a common pathogenesis is likely to overestimate the true probability.)


Finding	Result	Sensitivity	Specificity
[ + ] BinaxNOW Rapid Antigen test	+ 0 -	100%	99%
for P falciparum; UpToDate cites slightly lower numbers (~95% accuracy) this test is based on HRP-2 and aldolase antigens Study: Clin Infect Dis. 2009 Sep 15;49(6):908-13. PMID 19686072
[ + ] BinaxNOW Rapid Antigen test	+ 0 -	86%	99%
for P ovale / P vivax / P malariae this test is based on HRP-2 and aldolase antigens Study: Clin Infect Dis. 2009 Sep 15;49(6):908-13. PMID 19686072
[ + ] Fever, Thrombocytopenia, and Splenomegaly	+ 0 -	71%	88%
refugee children from West Africa; prevalence was 60% Study: Pediatr Infect Dis J 2005 May;24(5):450-2. PMID 15876946
[ + ] Leukocytosis		Sensitivity = 3%
> 9.8k cells/ul Study: Clin Infect Dis. 1998 Jul;27(1):142-9. PMID 9675468
[ + ] Leukopenia		Sensitivity = 48%
< 5k/ul Study: Clin Infect Dis. 1998 Jul;27(1):142-9. PMID 9675468
[ + ] Malaria PCR		No accuracy specified.
now regarded as the gold standard (previously, it was the blood smear). Also can be used to identify the species. Study: no study specified.
[ + ] Thick Blood Smear	+ 0 -	50%	100%
this is for all infections. Obviously, greater parasitemia yields greater sensitivity. In addition, sensitivity is greatly dependent on laboratory experience. It is recommended that smears be repeated every 6-12 hours until the diagnosis is confirmed (if there is clinical suspicion); sensitivity is pretty good at >100 parasites/ul. Finally - thick smears are more sensitive for detection of any malaria - while thin smears are generally used to better estimate parasitemia and identify the species. similar results from three studies re: sensitivity (see citations). Study: J Clin Microbiol. 2004 Jun;42(6):2694-700. PMID 15184454 J Infect Dis. 2009 Nov 15;200(10):1509-17. PMID 19848588 Clin Infect Dis. 1998 Jul;27(1):142-9. PMID 9675468
[ + ] Thick Blood Smear	+ 0 -	85%	100%
note the sensitivity disparity compared to the other entry (which was ~50%)... this is from US hospitals. Prevalence 11% in this population. Sensitivity was 88% for falciparum and 76% for vivax/ovale/malariae. Study: Clin Infect Dis. 2009 Sep 15;49(6):908-13. PMID 19686072
[ + ] Thrombocytopenia		Sensitivity = 83%
P vivax Study: Clin Infect Dis. 1998 Jul;27(1):142-9. PMID 9675468
[ + ] Thrombocytopenia		Sensitivity = 62%
P falciparum Study: Clin Infect Dis. 1998 Jul;27(1):142-9. PMID 9675468