When a lab report mentions “blasts” in the blood, it refers to immature, undeveloped blood cells. Their presence often signals an underlying medical condition. These cells are usually confined to the bone marrow, where they mature into functional blood components. Their appearance in the bloodstream is an important indicator for healthcare professionals.
Understanding Immature Blood Cells
All blood cells originate from hematopoietic stem cells within the bone marrow, the soft, spongy tissue inside bones. This process, known as hematopoiesis, ensures a supply of new blood cells. Stem cells develop into precursor cells, called “blasts,” which are committed to becoming specific types of mature blood cells. For instance, myeloblasts mature into various white blood cells, red blood cells, and platelets, while lymphoblasts become lymphocytes, a type of white blood cell involved in the immune system.
These immature blast cells develop within the bone marrow before fully maturing. In a healthy individual, blasts constitute less than 5% of the cells in the bone marrow. They are not found circulating in the peripheral bloodstream of healthy adults. Once mature, these specialized blood cells are released into the bloodstream to perform functions such as carrying oxygen, fighting infections, or clotting blood.
When Blasts Increase
An elevated number of blasts in the blood or bone marrow indicates a serious underlying condition. The most prominent cause is acute leukemia, a blood cancer where immature blasts multiply excessively and fail to mature. These abnormal cells accumulate, crowding out healthy blood cell production in the bone marrow and often spilling into the bloodstream. Acute myeloid leukemia (AML) involves an overproduction of myeloblasts, while acute lymphoblastic leukemia (ALL) is characterized by an increase in lymphoblasts.
Myelodysplastic syndromes (MDS) also involve an increase in blasts, between 5% and 19% in the bone marrow, where these cells do not mature as they should. About one-third of individuals with MDS may eventually develop AML. Less commonly, an increase in blasts can be observed in other contexts, such as severe infections, medical treatments like granulocyte-colony stimulating factor (G-CSF), or after stem cell transplants. In these non-cancerous situations, the blasts appear normal and retain the capacity to mature, unlike those seen in leukemia.
How Blasts Are Identified
The initial step in assessing blood cell populations involves a complete blood count (CBC) with differential. This test measures red blood cells, white blood cells, and platelets, indicating abnormalities that prompt further investigation. If CBC results suggest an issue, a peripheral blood smear is performed. For this test, a small blood sample is spread on a glass slide and examined under a microscope by a pathologist.
The pathologist identifies and counts the different types of blood cells, including the presence and morphology of blasts. This assessment helps determine if blasts are present, their quantity, and if they appear abnormal. Because blasts originate in the bone marrow, a bone marrow biopsy and aspiration may be necessary to confirm a diagnosis. This procedure involves taking a small sample of bone marrow, usually from the hip bone, for detailed analysis to determine the percentage and characteristics of blasts within their primary production site.
Interpreting Blast Counts
The percentage of blasts found in the blood or bone marrow guides diagnosis and treatment planning. A count of 20% or more blasts in the bone marrow or peripheral blood is a criterion for diagnosing acute leukemia. Even if slightly lower but still elevated, especially with other laboratory findings, it can indicate a serious bone marrow disorder like myelodysplastic syndrome.
The implications of an elevated blast count are significant, often pointing to a condition that impairs the body’s ability to produce healthy blood cells. This can lead to various complications, including anemia, increased risk of infection, and bleeding problems. The specific type and percentage of blasts inform healthcare providers about the nature and potential aggressiveness of the condition. Consulting with a doctor is necessary for an accurate interpretation of these results and to determine the appropriate next steps for care.