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Blood Smear
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Blood Smear

A blood smear is a diagnostic test that examines blood cells under a microscope to help identify blood disorders, infections, and certain types of cancer.

What is a blood smear?

A blood smear is a test used to diagnose and monitor blood disorders and other conditions. A sample of your blood is spread on a glass slide, treated with a special stain, and examined under a microscope to check the size, shape, and number of your red blood cells, white blood cells, and platelets.

Why do I need a blood smear?

You may need a blood smear if you have had abnormal results on a complete blood count (CBC) or if you exhibit symptoms such as fatigue, jaundice, unusual bleeding, easy bruising, fever, bone pain, or swollen lymph nodes. It is also used to monitor treatment for conditions like anemia or blood cancer, and to detect parasitic diseases like malaria or babesiosis.

What happens during a blood smear?

A health care professional will take a blood sample from a vein in your arm using a small needle. In some cases, a finger prick or heel prick (for infants) may be used. The procedure is quick, typically taking less than five minutes.

What do the results mean?

A blood smear alone cannot diagnose a condition; it is used alongside your medical history and other test results. Abnormal findings may indicate:

  • Red blood cell issues: Potential signs of anemia, sickle cell disease, or thalassemia.
  • White blood cell issues: Potential signs of infection or leukemia.
  • Platelet issues:Thrombocytopenia (low platelets, increasing bleeding risk) or thrombocytosis/thrombocythemia (high platelets, which may increase the risk of blood clots).

Other factors, such as severe illness, stress, or blood transfusions, can also influence your results. If your results are abnormal, your provider will likely order further testing to determine the underlying cause.

Frequently Asked Questions

high proportion of blasts suggests the bone marrow is releasing cells before they mature, which can be seen in acute leukemias or severe infections. Your doctor will likely order additional tests such as flow cytometry, cytogenetics, and a bone‑marrow biopsy to determine the exact cause.
Most laboratories report findings within 24‑48 hours after the sample is collected. If urgent (e.g., suspected infection or leukemia), the lab can prioritize the slide and provide a preliminary report within a few hours.
Yes, a stained smear can identify malaria parasites inside red blood cells. If you develop fever, chills, or flu‑like symptoms after travel to a malaria‑endemic region, seek medical care promptly and request a malaria smear or rapid diagnostic test. Early treatment reduces complications.
smear can reveal abnormalities that a CBC misses, such as abnormal cell shapes, immature cells, or parasites. Even with normal counts, symptoms like unexplained fatigue, bruising, or fever may prompt a smear to look for early signs of anemia, infection, or hematologic malignancy.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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