An approximate number of malaria parasite forms in the peripheral blood can be estimated by counting the number of parasites for a given number of white blood cells.
malaria count in the peripheral blood =
= (((number of parasites counted) / (number of white cells counted)) * (WBC count))
where:
• The number of white cells counted varies with the parasite load. At high levels of parasitemia, 50 WBCs is sufficient. At low levels of parasitemia, larger numbers of white blood cells should be counted to get meaningful results.
• WBC count is the white blood cell count per microliter. The number of white cells to count can vary depending if neutropenia or neutrophilia is present.
Interpretation:
• The count derived is used initially as a rough estimate of parasite load, but is used primarily to assess the effectiveness of therapy.
• The counts should drop to 0 with effective therapy.
• Fulminant disease will show rising levels of organisms.
• Organisms showing drug resistance to current regimen should show no or minimal changes in numbers.
Limitations: In Plasmodium vivax infections parasites may be cleared from the blood yet the patient have disease relapse unless "radical cure" of intrahepatic forms is achieved.
