Malaria Testing 2022

Why Test for Malaria?

• Malaria risk increases after travel to endemic regions, especially following seasonal rains.
• Taxi malaria may occur even without travel, when infected mosquitoes are transported via vehicles.
• Every patient with unexplained fever should be tested for malaria, even in non-endemic areas.
• Malaria transmission is increasing across southern Africa as the season progresses.

Available Malaria Tests

Standalone Tests:

• MALA – Rapid diagnostic test (antigen detection)
• MA – Peripheral blood smear (PBS)
• QBCN – Automated flow cytometry (XN31)
• MALPCR – Malaria PCR
• MALIDPCR – Malaria identification PCR

Combination Tests:

• MAL – RDT + PBS
• MALQ – RDT + PBS + flow cytometry

Best Practice

• Peripheral blood smear (PBS) remains the WHO gold standard.
• Repeat testing every 6–12 hours for up to 48 hours if malaria is suspected but initial results are negative.
• Parasite levels may be suppressed by certain antibiotics and antimalarials, making early detection more difficult.

Test Summaries

Rapid Antigen Detection Test (RDT)

• Use case: First-line testing
• Advantages:
  • Quick and affordable
  • Good for detecting P. falciparum
• Limitations:
  • May remain positive up to 2 weeks after treatment
  • Can produce false positives and false negatives
  • Limited ability to detect or speciate non-falciparum infections
  • Not suitable for follow-up monitoring

Thick Smear

• Use case: Diagnostic confirmation
• Advantages:
  • Higher sensitivity than thin smear
  • Detects a range of parasite stages
  • Affordable
• Limitations:
  • Slower due to the need to scan hundreds of fields
  • Operator skill-dependent
  • Not ideal for speciation

Thin Smear

• Use case: Speciation and treatment monitoring
• Advantages:
  • Allows species identification
  • Useful for quantifying parasite load
  • Detects ring forms and schizonts
  • Cost-effective
• Limitations:
  • Less sensitive than thick smear
  • Depends on operator expertise

Automated Flow Cytometry (XN31)

• Use case: Confirmation and quantification
• When to add:
  • Discrepant results between RDT and smear
  • Unclear speciation
  • Monitoring parasite burden
• Advantages:
  • High sensitivity (~20 parasites/µL)
  • Includes PBS and FBC (without WBC differential)
  • Quick and objective
• Limitations:
  • Cannot distinguish specific non-P. falciparum species
  • Higher cost
  • Sample must reach the lab within 48 hours (kept at 2–8°C)

Malaria PCR

• Use case: High clinical suspicion with negative smear/RDT
• When to add:
  • Suspected false positives
  • Early infection
• Advantages:
  • Very high sensitivity
  • Effective even in low parasitaemia
• Limitations:
  • Can remain positive after treatment
  • TAT may vary by lab
  • Higher cost

Malaria Identification PCR

• Use case: Accurate speciation
• When to add:
  • Speciation needed in low-level or mixed infections
• Advantages:
  • Detects P. falciparum, P. malariae, P. ovale, P. vivax
• Limitations:
  • Does not detect P. knowlesi
  • More expensive
  • Lab location may affect TAT

Important Notes

• QBC (buffy coat fluorescence) is no longer offered.
• Follow-up testing with smears is important for patients under treatment.
• If malaria is suspected, retesting at intervals may be necessary, especially when recent antimicrobial therapy may interfere.