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Trop Med Int Health. 2018 Sep;23(9):980-991. doi: 10.1111/tmi.13124. Epub 2018 Jul 17.

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

Author information

1
Division of Infectious Diseases and Tropical Medicine, Department of Medicine I, Medical University of Vienna, Vienna, Austria.
2
Centre de Recherches Médicales de Lambaréné, Lambaréné, Gabon.
3
Institut für Tropenmedizin, German Centre for Infection Research, partner site Tübingen, Universität Tübingen, Tübingen, Germany.
4
Department of Tropical Medicine, Bernhard Nocht Institute for Tropical Medicine & I. Department of Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
5
Malaria Clinical and Operational Research Unit, Melen Hospital, Département de Parasitology, Université des Sciences de la Santé Gabon, Libreville, Gabon.
6
German Centre for Infection Research (DZIF), partner site Hamburg-Luebeck-Borstel, Hamburg, Germany.

Abstract

OBJECTIVES:

The recommended microscopy method by WHO to quantify malaria parasitaemia yields inaccurate results when individual leucocyte (WBC) counts deviate from 8000 leucocytes/μl. A method avoiding WBC count assumptions is the Lambaréné method (LAMBA). Thus, this study compared validity and reliability of the LAMBA and the WHO method.

METHODS:

Three methods for counting parasitaemia were applied in parallel in a blinded assessment: the LAMBA, the WHO method using a standard factor of 8000 leucocytes/μl ['simple WHO method' (sWHO)] and the WHO method using measured WBC counts ['accurate WHO method' (aWHO)]. Validity was assessed by comparing LAMBA and sWHO to the gold standard measurement of aWHO. Reliability was ascertained by computation of intraclass correlation coefficients (ICCs).

RESULTS:

787 malaria-positive thick smears were analysed. Parasitaemia as determined by LAMBA and sWHO increasingly deviated from aWHO the more patients' WBCs diverged from 8000/μl. Equations of linear regression models assessing method deviation in percent from gold standard as function of WBC count were y = -0.00608x (95% CI -0.00693 to -0.00524) + 47.8 for LAMBA and y = -0.0125x (95% CI -0.01253 to -0.01247) + 100.1 for sWHO. Comparison of regression slopes showed that the deviation was twice as high for sWHO as for LAMBA (P < 0.001). ICCs were excellent (>90%) for both methods.

CONCLUSIONS:

The LAMBA has higher validity than the sWHO and may therefore be preferable in resource-limited settings without access to routine WBC-evaluation.

KEYWORDS:

Paludisme; diagnostics; fiabilité; leucocytes; light microscopy; malaria; methods; microscopie optique; méthodes; plasmodium; prévision; reliability; validity; validité

PMID:
29956431
DOI:
10.1111/tmi.13124

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