Thursday, October 13, 2011

Why is My Platelet Count Low?

Sometimes you just go for a routine blood test and you are told that your platelet count is abnormally low. The doctor may ask you whether you have easy bruising, red dots on your skin (petechiae), delayed blood clotting or spontaneous bleeding. You may or may not have these problems. What actually cause your platelet to be low?

Platelet is one of the 3 major types of blood cells produced in the bone marrow, besides red blood cells and white blood cells. Platelet is important in the process of blood clotting. If your platelet count is too low or not functioning, then you may have easy bleeding problem. The medical term of low platelet is thrombocytopenia.

      red cell, platelet, white cell

Normal range of platelet count is between 150,000-450,000/mcL. If you find that your platelet count is low for the first time and you do not have any symptoms, you can repeat the test as sometimes during blood taking and processing, the platelets may clump. If 10 platelets clump together, the machine may read it as only one platelet.

Though platelet count <150,000/mcL is considered low, it usually will not cause bleeding problem as long as their function is not affected. Spontaneous bleeding may be a concern if the count is <20,000/mcL.

There are many possible causes of thrombocytopenia. They can be classified into 3 large groups.
  1. Reduced production in bone marrow
  2. Increased destruction (by immune system or not)
  3. Splenic sequestration (due to enlarged spleen)

The list below are not comprehensive, only the important and common ones listed.
  • Reduced production in bone marrow
    • some viral infection (HIV, EBV, parvovirus, mumps, rubella, varicella, dengue)
    • some medication (thiazides, phenytoin, valproate)
    • alcohol
    • chemotherapy
    • radiation to the marrow
    • leukemia
    • lymphoma
    • cancer infiltrating the bone marrow 
    • vitamin B12/Folic acid deficiency
  • Increased destruction
    • Idiopathic Thrombocytopenic Purpura (ITP)
    • Autoimmune diseases (Systemic Lupus Erythemathosus)
    • Drugs-induced (heparin, sulfonamides antibiotics, quinine, quinidine, carbamazepines, digoxin, paracetamol / acetaminophen)
    • Sepsis (severe systemic infection)
    • Disseminated Intravascular Coagulation (DIVC)
  • Platelet sequestration
    • chronic liver disease (cirrhosis)
    • leukemia
    • lymphoma

If you have thrombocytopenia, you should check the numbers of your red and white blood cells. If they are normal, then it is less likely that the whole bone marrow is affected. The doctor will ask you some questions to find out any relation to the causes listed above, such as the medication you take, whether you have recent infection, your alcohol consumption, hepatitis status and other associated symptoms etc. 

      petechiae can be a sign of low platelet

A peripheral blood film / full blood picture should be done to see the size, shape and characteristic of all 3 types of blood cells. Sometimes a bone marrow aspiration may be done to rule out abnormality in the marrow. If no cause can be found after extensive investigation, and the platelet count is persistently low, steroid treatment may be given as a trial. If the platelet count increase significantly after steroid treatment, then it is likely to be idiopathic thrombocytopenic purpura, where the low platelet count is caused by immune system mediated platelet destruction.

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