Thrombocytopenia (Low Platelet Count)

  • Medical Author:
    Siamak N. Nabili, MD, MPH

    Dr. Nabili received his undergraduate degree from the University of California, San Diego (UCSD), majoring in chemistry and biochemistry. He then completed his graduate degree at the University of California, Los Angeles (UCLA). His graduate training included a specialized fellowship in public health where his research focused on environmental health and health-care delivery and management.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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How is thrombocytopenia diagnosed?

Thrombocytopenia is usually detected incidentally from routine blood work done for other reasons. Platelets are a component of the complete blood count (CBC) which also contains information on red blood cells and white blood cells.

If thrombocytopenia is seen for the first time, it is prudent to repeat the complete blood count in order to exclude pseudothrombocytopenia (see above). If the repeat CBC confirms low platelet counts, then further evaluation can begin.

Once detected, the cause of thrombocytopenia may be investigated by the doctor. The most essential part of this evaluation includes a thorough physical examination and medical history of the patient. In the medical history, the complete list of all medications is routinely reviewed. Some of the other important components of the history include reviewing previous known history of low platelet count, family history of thrombocytopenia, recent infections, any previous cancers, other autoimmune disorders, or liver disease.

A review of the symptoms related to excessive bleeding or bruising can also provide additional information. As a part of a thorough physical examination, special attention may be given to the skin and mucus membrane in the oral cavity for petechiae or purpura or other signs of bleeding. On the abdominal examination, an enlarged spleen (splenomegaly) can provide important diagnostic clues.

The urgency to perform additional testing and evaluation is largely dependent on how low the platelet count is on the blood count, and what the clinical situation may be. For instance, in a person who needs a surgery and has a platelet count of less than 50,000 the investigation will take precedence over one whose thrombocytopenia was detected on a yearly blood work with a platelet of 100,000.

A comprehensive review of the other components of the CBC is one of the most important steps in the evaluation of low platelet count. The CBC can tell us whether other blood disorders may be present, such as, anemia (low red cell count or hemoglobin), erythrocytosis (high red blood cell count or hemoglobin), leukopenia (low white cells count), or leukocytosis (elevated white blood cell count). These abnormalities may suggest bone marrow problems as the potential cause of thrombocytopenia. Abnormally shaped or ruptured red cells (schistocytes) seen on the blood smear may suggest evidence of HELLP, TTP, or HUS (see above).

Another clue in the CBC is the mean platelet volume or MPV, which is an estimate of the average size of platelets in the blood. A low MPV number may suggest platelet production problem, whereas, a high number may indicate increased destruction.

It is important to also review other blood work including the complete metabolic panel, coagulation panel, and urinalysis. Certain abnormalities in these tests can suggest advanced liver disease (cirrhosis), kidney problems (renal failure), or other pertinent underlying medical conditions.

In some causes of thrombocytopenia, such as HIT or ITP, additional testing with antibodies may be useful. Bone marrow biopsy may sometimes be performed if a bone marrow problem is suspected.

Medically Reviewed by a Doctor on 4/30/2015

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