Validity and reliability of methods to microscopically detect and quantify malaria parasitaemia

Area of Science:

• Medical Parasitology
• Diagnostic Microbiology
• Public Health

Background:

• The World Health Organization (WHO) microscopy method for quantifying malaria parasitaemia relies on an assumed white blood cell (WBC) count of 8000/μl.
• Deviations in individual WBC counts from this assumption lead to inaccurate malaria parasite quantification.
• The Lambaréné method (LAMBA) offers an alternative that does not depend on WBC count assumptions.

Purpose of the Study:

• To compare the validity and reliability of the LAMBA method against the WHO microscopy method for malaria diagnosis.
• To assess the impact of varying WBC counts on the accuracy of both diagnostic methods.

Main Methods:

• A blinded assessment was conducted using three parallel methods: LAMBA, the simple WHO method (sWHO) using a standard WBC factor, and the accurate WHO method (aWHO) using measured WBC counts.
• Validity was determined by comparing LAMBA and sWHO against the gold standard aWHO.
• Reliability was evaluated using intraclass correlation coefficients (ICCs).

Main Results:

• Parasitaemia quantification by LAMBA and sWHO increasingly deviated from the aWHO standard as patient WBC counts diverged from 8000/μl.
• The deviation from the gold standard was twice as high for the sWHO method compared to the LAMBA method (P < 0.001).
• Both methods demonstrated excellent reliability with ICCs above 90%.

Conclusions:

• The LAMBA method exhibits higher validity than the simple WHO method for malaria parasitaemia quantification.
• LAMBA is a preferable diagnostic method in resource-limited settings where routine WBC counts are not readily available.