The blood smear test 
The thick blood film smear test 
The QBC-malaria test® 

Detection of HRP2

• Other tests are under preparation, some in the assessment phase. The target may be the detection of plasmodium LDH. The multi-species tests are for the future.  
• The highlighting of the parasitic antigens in the infected erythrocytes, solubilized then revealed by radio-immunotitration or by immunoenzymatic techniques (ELISA), have been described. They remain poorly adapted for routine diagnosis due to the difficulty to standardize the reagents used and to eliminate all the antimalarial antibodies from the sample tested. 

These techniques are based on the detection of sequences characteristic of plasmodium genomic DNA by means of catheters of denatured DNA containing a complementary nucleotidic sequence of a repetitive sequence of the parasitic DNA. The PCR (polymerase chain reaction) improves the hybridation techniques by selectively amplifying a region of the genome of the parasite. But these techniques are still in the domain of the research laboratory and are not adapted to the emergency.

This technique uses a flow cytometer, a sophisticated and costly device, which limits its use to a few well-equipped laboratories with highly qualified staff. 

It has been proven capable of revealing automatically the parasite infected red blood cells after marking the parasitic DNA with thiazol orange. This is a very sensitive technique, providing quantification of the parasitemia, and specific but not providing a differentiation of the species.

The blood smear test:

• Detection threshold: 100 HPM (infected RBCs per microliter), i.e. 0.0025 %, i.e. 1 parasite for 200 fields. 
• Advantages: the smear test provides a diagnosis of species, a study of the plasmodium density and that of the associated hematological signs. It is suitable for emergency use. It also provides diagnosis of other pathogenic sanguicolous agents. Finally, it enables a deferred reading in time and space, and thus a control to be made. 
• Drawbacks: it requires a good technical performance, the reading is long (20 minutes), the threshold of detection is high and training is indispensable.   

The QBC Malaria Test®:

• Detection threshold: 1 HPM. 
• Advantages: the detection threshold is low, the test is adapted to emergency use, the diagnosis of other pathogenic sanguicolous agents is possible, the training is simple for staff familiar with the reading of the blood smear test. 
• Drawbacks: the equipment is expensive, the test does not provide a species diagnosis, a study of the plasmodium density nor that of the associated hematological signs; the training requires a prior learning of the reading of a blood smear test; the deferred reading in time is limited to five days.   

Detection of HRP2:

• Detection threshold: estimated at 10 HPM. In practice, detection of HRP2 is always positive if the parasitic density is 0.01 %. 
• Advantages: the technique provides a diagnosis of the infection by Plasmodium falciparum. It is adapted to emergency and to use in the field. Its apprenticeship is simple. HRP2 clearance being longer than the parasitic clearance, the technique provides a retrospective diagnosis of infection by Plasmodium falciparum. Finally, it enables a deferred reading in time and space.. 
• Drawbacks: the technique is strictly specific to Plasmodium falciparum. It does not help in the diagnosis of other sanguicolous pathogenic agents, the study of the plasmodium density nor that of associated hematological signs.