Antigen-based Rapid Diagnostic Tests (RDTs) play an important role in the diagno

Question

Antigen-based Rapid Diagnostic Tests (RDTs) play an important role in the diagnosis of malaria since it is a curable disease if detected early and treated promptly. In a retrospective study, scientists compared RDT results against the results of microscopic examination of blood films, which is the gold standard for confirming disease status. The results are shown in the table below. a) Determine the sensitivity of the RDT. b) Calculate the specificity of the RDT. c) What is the positive predictive value of the antigen-based rapid diagnostic test, given that the probability of contracting malaria in a population in sub-Saharan Africa is 8%?

Explanation / Answer

A) sensitivity = (198)/(198+8) = 0.9612

B) specificity = 767/794 = 0.966

C) positive predictive value = P(actually having disease | tested positive)

P(test positive)= 0.08x0.9612 + 0.92x(1-0.966)

= 0.1082

P(testing positiveand actually having disease) = 0.08x0.9612 = 0.0769

Positive predictive value = 0.0769/0.1082 = 0.7107

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