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What platelet count indicates leukemia?

Platelets, also called thrombocytes, are colorless blood cells that help blood clot. A normal platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. A platelet count below this normal range indicates a condition called thrombocytopenia. There are many potential causes of thrombocytopenia, one of which is leukemia.

What is leukemia?

Leukemia is a cancer of the blood and bone marrow, the spongy tissue inside bones where blood cells are made. With leukemia, the bone marrow produces abnormal white blood cells, which don’t function properly and crowd out healthy cells. This results in fewer normal red blood cells, white blood cells and platelets.

There are several main types of leukemia:

  • Acute lymphoblastic leukemia (ALL): Develops from immature forms of lymphocytes, a type of white blood cell
  • Acute myeloid leukemia (AML): Develops from immature forms of myeloid cells, another type of white blood cell
  • Chronic lymphocytic leukemia (CLL): Develops from abnormal lymphocytes that multiply slowly over time
  • Chronic myeloid leukemia (CML): Develops from abnormal myeloid cells that multiply slowly over time

Both acute and chronic leukemias can cause low platelet counts, but thrombocytopenia is more common with the acute types that progress rapidly.

What causes low platelets in leukemia?

There are a few reasons why platelet counts drop in leukemia:

  • The abnormal leukemia cells crowd out megakaryocytes, which are the bone marrow cells responsible for platelet production.
  • Chemotherapy and radiation treatments for leukemia can damage the bone marrow’s ability to make platelets.
  • Some leukemia cells can destroy platelets more rapidly than they are produced.

Thrombocytopenia is most severe when the leukemia is active or progressing. Platelet counts tend to improve when the leukemia is controlled with treatment.

What is considered a low platelet count?

Doctors diagnose thrombocytopenia when the platelet count falls below 150,000 per microliter. Thrombocytopenia can be categorized as:

  • Mild: 100,000 to 150,000 platelets per microliter
  • Moderate: 50,000 to 100,000 platelets per microliter
  • Severe: Below 50,000 platelets per microliter

Dangerously low counts below 10,000 platelets per microliter can lead to spontaneous bleeding and bruising. This severe thrombocytopenia requires emergency treatment.

How low can platelet counts go with leukemia?

In acute leukemias like AML and ALL, platelet counts often fall below 50,000 per microliter. Counts below 20,000 are common, and some cases may have less than 10,000 platelets per microliter. Extremely low counts below 5,000 are possible.

Chronic leukemias like CML and CLL more commonly cause mild to moderate thrombocytopenia. However, platelet counts can occasionally drop into the severe range below 50,000 per microliter.

What are symptoms of low platelets?

Some common symptoms of thrombocytopenia include:

  • Bruising easily
  • Petechiae, which are tiny reddish-purple spots on the skin
  • Bleeding from the gums or nose
  • Blood in the urine or stool
  • Heavy menstrual bleeding in women
  • Prolonged bleeding from minor cuts
  • Fatigue, weakness and shortness of breath from anemia

Those with platelet counts below 10,000 per microliter are at high risk of severe, spontaneous bleeding in the brain and other critical organs.

How are low platelet counts diagnosed?

Thrombocytopenia is diagnosed with a blood test called a complete blood count (CBC). This test measures levels of all the different cells in the blood, including platelets.

If thrombocytopenia is detected on a CBC, the next step is to examine a blood smear under the microscope. This can provide clues about the cause. With leukemia, the blood smear usually shows abnormal, immature white blood cells.

Other blood tests can measure platelet production and destruction to determine why platelet counts are low. A bone marrow biopsy can confirm leukemia by revealing abnormal cells.

Can low platelets be the only sign of leukemia?

It is possible, but uncommon, for low platelet counts to be the only finding that leads to a leukemia diagnosis. In most cases, people also have abnormal white blood cell and hemoglobin levels on their CBC test.

However, thrombocytopenia may occasionally be the first or most prominent finding, before other blood cell abnormalities become apparent. So unexplained low platelets should always prompt further testing to investigate and rule out leukemia.

What platelet count is considered an emergency?

A platelet count below 10,000/microliter is considered a medical emergency requiring urgent treatment. At this level, there is a major risk of severe bleeding that can cause serious health complications or even become life-threatening.

Emergency steps will be taken to raise platelet levels and prevent bleeding. This may include platelet transfusions, medications, or surgery to remove the spleen.

Can low platelets be treated?

The treatment focus is on addressing the underlying cause – the leukemia itself. Chemotherapy, radiation, bone marrow transplant or other leukemia treatments can put the disease into remission and allow platelet counts to recover.

However, boosting platelet levels is also important to reduce bleeding risk in the short-term. This may involve:

  • Platelet transfusions to rapidly increase platelet counts
  • Medications such as romiplostim or eltrombopag that stimulate platelet production
  • If the spleen is trapping too many platelets, surgery to remove it (splenectomy)
  • Addressing other medication side effects that may be worsening thrombocytopenia

What is the outlook for low platelets with leukemia?

The prognosis depends most on the type of leukemia and how well it responds to treatment. In acute leukemias, platelet counts tend to improve after initiating chemotherapy and entering remission.

But chemotherapy can also suppress platelet production further before levels rebound. Platelet transfusions are often needed to manage low counts throughout leukemia treatment.

With chronic leukemias like CML, new targeted drugs can provide long-term control and allow normal blood cell levels to be maintained in many patients.


In summary, thrombocytopenia is a common complication of all types of leukemia. Platelet counts lower than 150,000 per microliter are considered abnormally low. Severe thrombocytopenia under 50,000 platelets is frequent with acute leukemias like ALL and AML. Treating the underlying leukemia can help improve platelet levels, but transfusions and medications may be needed to prevent serious bleeding issues.