What Causes a Low Platelet Count?

Have you been told that you have a low platelet count? If this was found on a blood test, you’re understandably concerned as to why. The medical term for a low platelet count is thrombocytopenia. This means you have less than 150,000 platelets per microliter of blood. Why is thisa problem? When the platelet counts drop, it increases the risk of bleeding from the nose and gums, and bruises can form more easily. The most serious risk is that the platelet count can fall so low that internal bleeding occurs. Fortunately, platelet counts usually have to drop pretty low (below 10,000 platelets per microliter) for this to happen. What causes a low platelet count?

One cause of a low platelet count is decreased platelet production by the bone marrow. A number of conditions can cause the bone marrow to stop producing enough platelets. Certain types of cancers such as leukemia or cancers involving the lymph system can do it.  More commonly, a viral infection can interfere with platelet production by the bone marrow. Some medications, vitamins deficiencies (B12 and folate), and even excessive alcohol intake can temporarily suppress the bone marrow causing a low platelet count. In rare cases, it can be due to a genetic condition or associated with kidney failure.

In some cases, normal amounts of platelets are made by the bone marrow, but they’re removed too quickly from the blood stream. Some viruses and drugs can cause this, although another cause is an autoimmune disease where antibodies are produced against platelets, causing them to be destroyed prematurely. There’s also a condition known as ITP (idiopathic thrombocytopenia purpura) where the immune system produces antibodies against its own platelets causing them to be destroyed.

In rare cases, an overwhelming infection, illness, or pregnancy will cause the blood clotting mechanism to be inappropriately turned on – a condition known as DIC. This is associated with the formation of small clots throughout the body. This causes the platelets to be used up and the platelet count to drop. With this condition, a person is usually quite ill.

Sometimes a low platelet count can be due to laboratory error such as clot in the sample. Repeating the platelet count will usually reveal the error.  

The bottom line? If you have a low platelet count is found on a lab exam, it’s important to follow up with a doctor and find out why. Sometimes simply repeating the blood count will reveal that the sample was simply clotted. If not, further studies may be needed.