Enough with the theory - let’s use some real world data now!

You want to assess the reliability of a rapid field test called Partec Rapid Malaria Test® (PT) for malaria diagnostic in comparison with the classical method of Giemsa stain microscopy (GM) considered as the gold standard.

Method
Blood samples are collected from 263 children admitted with fever to the paediatric clinic of the Agogo Presbyterian Hospital, Ghana. The two different test methods PT and GM are performed independently to assess the presence of malaria parasites. Results are analysed and compared using GM as the gold standard.

Results
Plasmodium sp. is detected by GM in 107 of 263 study participants. PT shows positive results in 111 positive for malaria and 107 slides has concordant results with GM.

Interpretation
Let’s interpret the results to fill in the 2x2 cross table:

• According to the gold standard test, 107 children have malaria. Thus, 263-107=156 children don’t have malaria.
• Among the 111 PT positive results, 107 are concordant with the results from GM. Thus, there is 107 true positive and 111-107=4 false positive results from the PT test.
• Consequently, the number of PT false negative is 107-107 = 0.
• The number of negative result from the PT test is 263-111=152.
• As there is no false negative, the number of PT true negative is 152.

Reference: Nkrumah, B., Acquah, S. E., Ibrahim, L., May, J., Brattig, N., Tannich, E. & Huenger, F. (2011). Comparative evaluation of two rapid field tests for malaria diagnosis: Partec Rapid Malaria Test® and Binax Now® Malaria Rapid Diagnostic Test. BMC infectious diseases, 11(1), 143