Malaria Parasite Smear (Thick/Thin Film)
A microscope exam of a blood sample that shows whether malaria parasites are present, which species they are and how many red cells are infected.
AI-verified against cited sources. Awaiting expert reviewAlso called BFMP, Malaria smearLOINC 32206-5
What it is
Malaria parasites live inside red blood cells. For this test a lab specialist spreads a drop of your blood on a slide, stains it with a dye (Giemsa) and looks for parasites under a microscope. A thick smear checks a larger amount of blood and is better at finding parasites. A thin smear shows the shape of the parasites and red cells, which helps identify the species and measure how many red cells are infected. The report usually names the species and gives the amount as a percentage of infected red cells or as parasites per microliter of blood.
Why it matters
A smear is the standard way to confirm malaria. It tells your care team the species and how heavy the infection is. Both guide treatment. A high percentage of infected red blood cells is one of the signs doctors use to spot severe malaria. A single negative smear does not completely rule malaria out, so repeat smears are often done.
If it’s low
No parasites seen means none were found in the part of the blood examined. It does not completely rule out malaria, because parasite numbers vary over time, especially early in an infection. If malaria is still suspected, smears are usually repeated every 12 to 24 hours for a total of three sets before malaria is considered ruled out.
Common causes
- You do not have malaria
- Parasite numbers too low to see on a single smear, especially early in infection
What can help
- If you keep having fever after travel, ask about repeat smears and other possible causes
- Tell your clinician if symptoms change
If it’s high
Parasites seen on the smear are a sign of malaria infection. The report should name the species and the percentage of infected red cells. The CDC lists a parasite density of 5% or more as one sign of severe malaria. Your care team will start treatment right away and will choose it based on the species, your symptoms and your medical history.
Common causes
- A malaria infection acquired from a mosquito bite, usually in a country where malaria is common
- Rarely, malaria passed on by a blood transfusion, an organ transplant or shared needles
What can help
- Tell your clinician exactly where and when you traveled, including trips up to a year ago
- Ask what the species and percentage on the report mean for your treatment and where you should be treated
What can affect your result
- How many parasites are in the blood at the time of the draw
- Recent antimalarial treatment
- The quality of the stain and the experience of the reader
- Whether the smear is thick (better for finding parasites) or thin (better for naming the species)
- Very few parasites early in an infection can be missed on a single smear (CDC advises repeating smears every 12 to 24 hours for three sets if the first is negative).
- Results depend on the quality of the stain and the experience of the person reading the slide.
- Recent antimalarial treatment can lower or clear parasites from the blood.
A smear shows the parasites in your blood at the moment of the draw. Counts vary over time, so one negative smear does not rule out malaria.
When to talk to a clinician
Get medical care promptly for fever, chills, headache or body aches during or after travel to a place where malaria occurs, even months later. Symptoms usually start 7 to 30 days after a bite but can take up to a year. If a smear is positive, follow your care team's treatment plan right away. Call 911 or your local emergency number for confusion, seizures or loss of consciousness.
Questions you could ask
- Does my travel history change which tests I should have?
- Which species of malaria is it, and what percentage of my red blood cells are infected?
- Do I need to be treated in a hospital?
- Do the people I traveled with need to be checked?
- If my fever continues, when should we repeat the smear?
- Should we look for other causes of fever after travel?
Questions people ask
What do the percentage and species on my report mean?
The species tells your care team which malaria parasite you have. The percentage is how many red blood cells contain parasites. Both help decide treatment and how closely you need to be watched. The CDC lists a parasite density of 5% or more as one sign of severe malaria.
My smear was negative. Does that rule out malaria?
Not by itself. Parasite numbers can be low early on, and they vary over time. When malaria is still suspected, the CDC advises repeating smears every 12 to 24 hours for a total of three sets before malaria is ruled out.
What is the difference between a thick and a thin smear?
A thick smear looks at more blood, so it is better at finding parasites. A thin smear spreads the cells out in a single layer, so it is better for naming the species and counting infected cells. Labs usually make both.
Show the science and sources
For clinicians and researchers
Giemsa-stained thick and thin blood films are the reference method for malaria diagnosis (CDC). Thick smears examine a greater volume of blood and are more sensitive. Thin smears aid species identification and quantification. Quantification can be done on either. Red cells with more than one parasite are counted once, and gametocytes are not counted when determining parasitemia. CDC lists a parasite density of 5% or more as one manifestation of severe malaria. Five Plasmodium species infect humans: P. falciparum, P. vivax, P. ovale, P. malariae and P. knowlesi (zoonotic). In non-immune patients, parasite densities may be low, so negative smears should be repeated every 12 to 24 hours for three sets before ruling malaria out. Rapid antigen tests (for example BinaxNOW) do not replace smears, because they cannot confirm species other than P. falciparum, determine parasitemia, or monitor treatment response, and should be followed by microscopy. Reports may give parasitemia as a percentage of infected red cells or as parasites per microliter. Labs differ in format.
LOINC 32206-5 (primary), 51587-4, 637-9, 10710-2, 101996-7. Specimen: whole-blood.
Sources
- Evaluation and Diagnosis of Malaria, CDC
- Malaria Tests, MedlinePlus (NIH)
- DPDx - Malaria, CDC
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.