Acridine orange detection of Plasmodium falciparum malaria: relationship between sensitivity and optical configuration

The reliability of diagnostic techniques in the diagnosis and management of malaria in the absence of a gold standard

The accuracy of techniques for the diagnosis of malaria are usually compared with optical microscopy, which is considered to be a gold standard. However, microscopy is prone to error and therefore makes it difficult to assess the reliability of other diagnostic techniques. We did a systematic review to assess the specificity and sensitivity of diagnostic techniques in different settings, using a statistical method that avoided defining a gold standard. Performance varied depending on species of the malaria parasite, level of parasitaemia, and immunity. Overall, histidine-rich protein 2 (HRP2)-based dipsticks showed a high sensitivity (92.7%) and specificity (99.2%) for Plasmodium falciparum in endemic areas. The acridine orange test was more sensitive (97.1%) in detecting P falciparum in epidemiological studies, with a specificity of 97.9%. In the absence of a gold standard, HRP2 dipsticks and acridine orange could provide an alternative for detecting falciparum infections in endemic areas and epidemiological studies, respectively. Microscopy still remains more reliable in detecting non-falciparum infections.

Comparison of acridine orange and giemsa stains for malaria diagnosis

Recently, the Acridine orange (AO) staining method has improved for identification of malaria parasites. Fixed and preserved blood smears of malaria patients were used for comparative analysis of AO and Giemsa stains. The AO staining method required less time and was more sensitive under lower magnification than the Giemsa staining method. The AO staining method provides an alternative to Giemsa for malaria diagnosis in the field and laboratory.

Evaluation of different methods for Plasmodia detection, in well defined population groups in an endemic area of Brazil (1)

In Brazil, more than 500,000 new cases of malaria were notified in 1992. Plasmodium falciparum and P. vivax are the responsible species for 99.3% of the cases. For adequate treatment, precoce diagnosis is necessary. In this work, we present the results of the traditional Plasmodia detection method, thick blood film (TBF), and the results of alternative methods: Immunofluorescence assay (IFA) with polyclonal antibody and Quantitative Buffy Coat method (QBC) in a well defined population groups. The analysis were done in relation to the presence or absence of malaria clinical symptoms. Also different classes of immunoglobulins anti-P.falciparum were quantified for the global analysis of the results, mainly in the discrepant results. We concluded that alternative methods are more sensitive than TBF and that the association of epidemiological, clinical and laboratory findings is necessary to define the presence of malaria.

Diagnosis of malaria in the field by fluorescence microscopy of QBC capillary tubes

The diagnostic performance of commercial capillary tubes containing acridine orange dye (QBC) was compared with the standard diagnosis of malaria by microscopical examination of Giemsa-stained thick blood films (GTS) in remote field conditions. The comparison was conducted among 165 volunteers living in northeastern Irian Jaya, Indonesia, an area having hyperendemic malaria transmission. By GTS, 65 volunteers were positive for malaria, but only 49 were judged positive by QBC. Among the 100 blood films found negative by GTS, 5 were considered positive by QBC. Thus, relative to a GTS standard, the sensitivity and specificity of the QBC was 75% and 95%, respectively. The mean limit of detection for the QBC was approximately 60 parasites per microliter blood, whereas the limit of detection for GTS was 20 parasites per microliter blood. Also, a number of practical difficulties were encountered using the QBC at the field site. The QBC approach to diagnosis of malaria was less sensitive and more inconvenient than GTS under the conditions in remote Irian Jaya.