Thick and Thin Blood Smears for Malaria
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
Why It Is Done
To date, microscopic examination of thick and thin blood smears is
the easiest and most reliable test for malaria.
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).
What To Think About
Blood smears are the most reliable tests for malaria. You may want
to ask whether a thick or thin blood smear, or both, is planned. A thin blood
smear will identify the species of the malaria parasite. This information is
important to prevent or anticipate life-threatening complications if
P. falciparum is the source of infection.
Complete the medical test information form (PDF)(What is a PDF document?) to help you prepare for this test.
Primary Medical Reviewer
||E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer
||W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
Current as of
||April 11, 2013