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Diagnostic Methods
Diagnostic methodsPros and cons
Parasitological diagnosis 

Microscopy (stained thick and thin blood films) has been the “gold standard” for malaria diagnosis for ages. However, the recent development of highly sensitive and specific molecular methods has changed this situation! PCR-based methods are now considered as the new “gold standard”. The detection limit using rt-PCR is 50 parasites/ml of whole blood. This is approx. 200 times lower than the detection limit of well-trained and experienced microscopists.

Blood smears should be prepared on admission of the patient even if there is no pattern of intermittent fever.
Both thick and thin blood smears should be prepared.
At least 200–300 oil immersion fields should be examined.
Giemsa is the stain of choice for blood parasites.

Note: malarial parasites may be missed using automated differential instruments.

  • Sensitivity and specificity depend highly on the skill of experienced microscopists
  • Differentiation of species is difficult after drug treatment has been started
Molecular diagnosis 

Different formats of PCR assays (conventional or real-time) have been developed allowing the confirmation of uncertain parasitological species determinations, the efficient detection of mixed infections or the detection of drug resistance markers.
In addition, molecular methods allow the genotyping of Plasmodium strains.

A new method, real-time Nucleic Acid Sequence-based Amplification (qt-NASBA) detects parasite RNS and is much faster than PCR!

  • Maximal sensitivity and excellent specificity
  • Need for PCR equipment and special skills
  • QT-NASBA is a 1000 times more sensitive than microscopy and results can be achieved within 1 hr.
Antigen detection 
Many commercially available rapid diagnostic tests (RDTs) detect histidine-rich protein-2 (HRP2) or parasite-specific lactate dehydrogenase (pLDH) by immunochromatographical procedures in whole-blood samples.
  • Simple test format; no microscopic skills and equipment needed
  • Somewhat less sensitive than parasitological diagnosis (false-negative results at low parasitaemia)
  • Limitations in species determination
  • Persistent antigens after therapy
Antibody detection 
The detection of anti-malarial serum antibodies is not adequate to diagnose an early acute infection. During the first febrile episode, no antibodies are detectable in most cases. Indications for serological investigations are restricted:
  • to diagnose relapses of P. vivax and P. ovale
  • to diagnose persistent malaria in persons returning with uncertain diagnosis from endemic areas
The most widely used serological test is IFA with P. falciparum parasites from culture. Home-made ELISA tests with crude or recombinant antigens have also been developed.
  • Be aware of false-negative results in the early acute phase!
  • Species-specific diagnosis is not possible
  • Persistent antibody titres after treatment