Blast Cells

What are blast cells?

Blast cells (or “blasts,” for short) are immature cells. Blasts give rise to all types of cells. But chances are, if you’ve encountered the term in a lab report — “blasts” means immature blood cells in particular. This is because specialists in blood disorders (hematologists and oncologists) use indicators like your blast cells to diagnose blood conditions.

Abnormal-looking blast cells or extremely high levels of blasts in your blood can be a sign of some blood cancers, like acute leukemia.

What is the difference between blood stem cells and blast cells?

Blood stem cells and blast cells account for different stages in normal cell development. Stem cells are originator cells that give rise to all other types of cells. Blast cells develop from stem cells. They’re also called “progenitor” or “precursor” cells because they come before (“pre”) the fully mature cell. Unlike a stem cell, a blast cell is set on a particular path to become one cell type or another.

What is the purpose of blasts?

On its own, a blast cell is just a stage in early blood cell development. Your body continually makes blood cells (including blasts) to replace the old ones during a process of blood formation called hematopoiesis. Hematopoiesis mostly takes place in your bone marrow.

Inside your bone marrow, a common originator cell called a hematopoietic stem cell (HSC) becomes one of two types of blasts:

• Myeloblast. A blast cell that gives rise to red blood cells, white blood cells (granulocytes, like monocytes, neutrophils, basophils and eosinophils) and platelets
• Lymphoblast. A blast cell that gives rise to white blood cells (lymphocytes)

Fully mature blood cells leave your bone marrow to circulate in your bloodstream. But the still-developing blast cells belong in your bone marrow — not your bloodstream. This is why circulating blasts in your blood on a lab report may signal a problem.

What causes elevated blasts?

In a lab report, high levels of blasts in your bone marrow or blood may be a sign of a blood cancer, like leukemia. This is especially the case if the cells look abnormal beneath a microscope. Under normal circumstances, only 5% of all blood cells in your bone marrow are blasts. You shouldn’t have any blasts in your blood.

Causes of elevated blasts include:

• Acute myeloid leukemia (AML)
• Myelodysplastic syndrome (MDS)
• Chronic myeloid leukemia (CML)
• Acute lymphoblastic leukemia (ALL)
• Some noncancerous conditions and treatments

Acute myeloid leukemia (AML)

Most medical conversations about blasts relate to acute myeloid leukemia. AML is an aggressive cancer, so timely diagnosis and treatment are especially important. Examining blast cells is an important tool for fast diagnosis.

With AML, abnormal blasts build up in your bone marrow and spill out into your blood. Most are myeloblasts that were in line to become white blood cells (granulocytes) before they became malignant.

The blasts are too immature and abnormal to serve any useful purpose. Instead, they take up so much space inside your bone marrow that they prevent the production of new blood cells you need. Without fully functioning mature blood cells, your body can’t function as it should.

Having 20% or more blasts in your bone marrow or blood is a sign of AML.

Myelodysplastic syndrome (MDS)

Myelodysplastic syndrome includes a group of blood cancers where blast cells don’t mature into normal blood cells. Often, the blasts die before reaching maturity. Having too many blasts and too few functioning mature blood cells can cause problems like anemia. It can cause frequent infections (because of a low white blood cell count). Or it can cause excessive bleeding or bruising (because of low platelets).

Having 5% to 20% blasts in your bone marrow is a sign of MDS. About 30% of people with MDS go on to develop AML.

Chronic myeloid leukemia (CML)

Chronic myeloid leukemia is a chronic (long-term) blood cancer that involves elevated blasts in your bone marrow or blood. Healthcare providers classify how serious it is based on your blast levels:

• Chronic Phase CML: Less than 10% of the cells in your blood or bone marrow are blasts
• Accelerated Phase CML: 10% to 19% of your blood cells are blasts
• Blast Phase CML (blast crisis): More than 20% of your blood cells are blasts, which is the same as with AML

Acute lymphoblastic leukemia (ALL)

Acute lymphoblastic leukemia is the most common cancer that affects children. With ALL, the bone marrow makes abnormal (cancerous) lymphoblasts. The abnormal cells divide rapidly and make several copies. This makes it harder for bone marrow to make normal cells your body needs.

With ALL, at least 20% of blood cells in your bone marrow are blasts. Most people diagnosed (90%) also have blasts in their blood.

Noncancerous causes

It’s important to remember, though, that elevated blasts on lab results don’t always mean cancer. Other conditions and circumstances can cause a temporary increase in blasts. These include:

• Serious infections: Blasts can spill out into your blood if your body has experienced a serious illness, like a severe infection (sepsis).
• Granulocyte-colony stimulating factor (G-CSF) treatment: Blasts may circulate in your blood after G-CSF treatment. These shots stimulate your bone marrow to make more white blood cells to protect you from infections. You may need them if you’re receiving chemotherapy or if you just tend to have low white blood cells (neutropenia).
• Stem cell transplants: You may have elevated blasts if you just received a stem cell transplant to treat a condition. You may need a stem cell transplant if you have a blood disorder, cancer or autoimmune disease that prevents your body from making normal blood cells.

Unlike blasts associated with cancer, these blasts usually appear normal beneath a microscope. They’re capable of maturing into normal blood cells.

What common tests check blast cell levels?

Tests that show blasts include:

• Peripheral blood smear (PBS): This test can show blasts in your blood. For a PBS, a pathologist views a sample of your blood beneath a microscope to check for elevated or abnormal-looking blasts.
• Bone marrow tests. Lab tests following a bone marrow biopsy or aspiration detect blasts in bone marrow. These may include flow cytometry, immunohistochemistry or fluorescence in situ hybridization (to check for genetic changes in cells).

You may also need a complete blood count (CBC) with differential to check your number of red and white blood cells and platelets. An increase in blast cells can cause your levels of healthy blood cells to decrease. Providers consider various test results and factors before diagnosing leukemia.