Rapid diagnostic tests for diagnosing uncomplicated <i>P. falciparum</i> malaria in endemic countries
Abstract
Background
Rapid diagnostic tests (RDTs) for Plasmodium falciparum malaria use
antibodies to detect either HRP-2 antigen or pLDH antigen, and can
improve access to diagnostics in developing countries.
Objectives
To assess the diagnostic accuracy of RDTs for detecting P. falciparum
parasitaemia in persons living in endemic areas who present to
ambulatory healthcare facilities with symptoms suggestive of malaria by
type and brand.
Search strategy
We undertook a comprehensive search of the following databases:
Cochrane Infectious Diseases Group Specialized Register; MEDLINE;
EMBASE; MEDION; Science Citation Index; Web of Knowledge; African Index
Medicus; LILACS; IndMED; to January 14, 2010.
Selection criteria
Studies comparing RDTs with a reference standard (microscopy or
polymerase chain reaction) in blood samples from a random or consecutive
series of patients attending ambulatory health facilities with symptoms
suggestive of malaria in P. falciparum endemic areas.
Data collection and analysis
For each study, a standard set of data was extracted independently by
two authors, using a tailored data extraction form. Comparisons were
grouped hierarchically by target antigen, and type and brand of RDT, and
combined in meta-analysis where appropriate.
Main results
We identified 74 unique studies as eligible for this review and
categorized them according to the antigens they detected. Types 1 to 3
include HRP-2 (from P. falciparum) either by itself or with other
antigens. Types 4 and 5 included pLDH (from P. falciparum) either by
itself or with other antigens. In comparisons with microscopy, we
identified 71 evaluations of Type 1 tests, eight evaluations of Type 2
tests and five evaluations of Type 3 tests. In meta-analyses, average
sensitivities and specificities (95% CI) were 94.8% (93.1% to 96.1%) and
95.2% (93.2% to 96.7%) for Type 1 tests, 96.0% (94.0% to 97.3%) and
95.3% (87.3% to 98.3%) for Type 2 tests, and 99.5% (71.0% to 100.0%) and
90.6% (80.5% to 95.7%) for Type 3 tests, respectively.
Overall for HRP-2, the meta-analytical average sensitivity and specificity (95% CI) were 95.0% (93.5% to 96.2%) and 95.2% (93.4% to 99.4%), respectively.
For pLDH antibody-based RDTs verified with microscopy, we identified 17 evaluations of Type 4 RDTs and three evaluations of Type 5 RDTs. In meta-analyses, average sensitivity for Type 4 tests was 91.5% (84.7% to 95.3%) and average specificity was 98.7% (96.9% to 99.5%). For Type 5 tests, average sensitivity was 98.4% (95.1% to 99.5%) and average specificity was 97.5% (93.5% to 99.1%).
Overall for pLDH, the meta-analytical average sensitivity and specificity (95% CI) were 93.2% (88.0% to 96.2%) and 98.5% (96.7% to 99.4%), respectively.
For both categories of test, there was substantial heterogeneity in study results. Quality of the microscopy reference standard could only be assessed in 40% of studies due to inadequate reporting, but results did not seem to be influenced by the reporting quality.
Overall, HRP-2 antibody-based tests (such as the Type 1 tests) tended to be more sensitive and were significantly less specific than pLDH-based tests (such as the Type 4 tests). If the point estimates for Type 1 and Type 4 tests are applied to a hypothetical cohort of 1000 patients where 30% of those presenting with symptoms have P. falciparum, Type 1 tests will miss 16 cases, and Type 4 tests will miss 26 cases. The number of people wrongly diagnosed with P. falciparum would be 34 with Type 1 tests, and nine with Type 4 tests.
Authors' conclusions
The sensitivity and specificity of all RDTs is such that they can
replace or extend the access of diagnostic services for uncomplicated P.
falciparum malaria. HRP-2 antibody types may be more sensitive but are
less specific than pLDH antibody-based tests, but the differences are
small. The HRP-2 antigen persists even after effective treatment and so
is not useful for detecting treatment failures.
Citation
Cochrane Database of Systematic Reviews 2011, Issue 7. Art. No.: CD008122. [DOI: 10.1002/14651858.CD008122.pub2.]