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Thick and Thin Blood Smears for Malaria

British Columbia Specific Information

Malaria is a very serious disease caused by mosquito bites and tiny parasites that get into and multiply in the bloodstream. Symptoms may include headache, abdominal pain, chills, shaking, fever and sweats. Malaria can cause seizures, anemia, jaundice, heart failure, kidney failure, coma, and even death. To learn about malaria and how it can be prevented, see HealthLinkBC File #41f Malaria Prevention, BC Centre for Disease Control - Malaria, and Government of Canada – Malaria.

For specific information on protecting yourself or your children when travelling, see HealthLinkBC File #41a Health Advice for Travellers, HealthLinkBC File #41g The Pregnant Traveller, and HealthLinkBC File #41d Travelling with Children.


Thick and Thin Blood Smears for Malaria—Overview

Doctors use thick and thin blood smears to determine whether you have malaria. If one test is negative and no parasites are found, you will have repeated blood smears every 8 hours for a couple of days to confirm that there is no malaria infection.

Blood smears are taken most often from a finger prick. Thick and thin blood smears will let doctors know the percentage of red blood cells that are infected (parasite density) and what type of parasites are present.

  • A thick blood smear is a drop of blood on a glass slide. Thick blood smears are most useful for detecting the presence of parasites, because they examine a larger sample of blood. (Often there are few parasites in the blood at the time the test is done.)
  • A thin blood smear is a drop of blood that is spread across a large area of the slide. Thin blood smears helps doctors discover what species of malaria is causing the infection.

Why It Is Done

Thick and Thin Blood Smears for Malaria—WhyDoneOrUsed

Microscopic examination of thick and thin blood smears is a reliable and widely available test for malaria.


Thick and Thin Blood Smears for Malaria—Results

Results of thick and thin blood smears may show:


No parasites are present in red blood cells. Your doctor will repeat the test every 8 hours for 1 or 2 days if he or she still suspects that you have malaria.


Parasites are present in red blood cells. The infecting species of Plasmodium is identified. Also, the percentage of red blood cells infected by the Plasmodium parasite (density) is determined.

Treatment may vary depending on the:

  • Species of Plasmodium present. Malaria caused by P. falciparum is more serious than other types and may be treated differently.
  • Percentage of red blood cells infected (parasite density), not the number of parasites. If a large percentage of blood cells is infected, medicine may be given directly into a vein (intravenously, or IV) instead of by mouth (orally).


Current as of: September 8, 2022

Author: Healthwise Staff
Medical Review:
E. Gregory Thompson MD - Internal Medicine
Anne C. Poinier MD - Internal Medicine
Adam Husney MD - Family Medicine
W. David Colby IV MSc, MD, FRCPC - Infectious Disease