What causes a Low Platelet Count in Humans?

Platelets (a.k.a thrombocytes) are anucleate (without nucleus) cell fragments present in blood, that respond to bleeding, from an injury to a blood vessel, by plugging the bleed and initiating a clot formation. Platelets are produced mainly from multi-nucleated giant cells in bone marrow, called Megakaryocytes, especially in response to a hormone called Thrombopoietin. Platelets are present in blood circulation as inactive forms and get activated when there is an injury to blood vessel. Old platelets are ultimately destroyed in the spleen platelet count​

A normal in peripheral blood (In humans) is 150 – 400 x 10³ per microlitre of blood (some labs may give ranges up to 450x10³). Any value less than 1.50 lakh per microlitre is known as THROMBOCYTOPENIA. Levels more than 4.50 lakh is known as THROMBOCYTOSIS. The usual size/diameter of a mature platelet is 2-3 microns. Sometimes immature platelets or large platelets of variable sizes are seen in peripheral blood, especially in patients with rapid turnover of platelets, due to some diseased states. This can be assessed by Mean Platelet Volume (MPV) which is given by automated cell counters. Higher the MPV, larger will be the size of platelets analysed. A normal MPV ranges from 6-11 fL.

Thrombocytopenia (low platelet counts) is usually picked up on a blood test called Complete Blood Count or Hemogram. Automated cell counters can measure platelet counts accurately and very fast. A manual platelet count also can be done by analysing blood samples under a microscope.

Signs and symptoms of Low Platelet Count (Thrombocytopenia)

Clinical presentation of a low platelet count varies from patient to patient. In most patients, mild to moderate decrease in platelets may go unnoticed and may be incidentally detected on a lab test. Some patients of Chronic Immune Thrombocytopenia (ITP) may have counts as low as 10,000-20,000 platelets per microlitre of blood and can still manifest no symptoms/signs. On the other hand, some with low platelet counts may show signs of external bleeding such as nose and gum bleeds, spontaneous petechial or purpuric rashes under the skin, prolonged or heavier periods in women, prolonged bleeding episodes etc. Heavy bruising with minor trauma can be expected in thrombocytopenia patients.

Causes of Thrombocytopenia

There are multiple causes for low platelet counts. Thrombocytopenia can be an inherited condition (runs in the family) or an acquired condition (secondary to some other condition). Conditions that affect platelet production and hence causing thrombocytopenia are:

Conditions that result in increased destruction of platelets

Some drugs can directly suppress production of platelets in the bone marrow such as Valproic acid, Methotrexate, Carboplatin, Isotretinoin, Interferon etc. Certain snake bites can also result in acquired thrombocytopenia.

How to detect Thrombocytopenia?

Low platelets can be detected by a simple platelet count or complete blood counts. In some cases, depending on the cause, a bone marrow study may be required to analyse the cause for decreased platelet production.

What is the treatment?

Treatment varies from condition to condition, which is primarily to eliminate the underlying cause in acquired disorders. Sometimes a splenectomy (removal of spleen) or addition of steroid medications can help in bringing the platelet count up. Platelet transfusions are beneficial in some conditions. Bone marrow/ Stem cell transplants may help in certain conditions.

Dr. Adithya S

Consultant Pathologist
MD Pathology