Thrombocytopenia (or -paenia, or thrombopenia in short) is the presence of relatively few platelets in blood. more...
Generally speaking a normal platelet count ranges from 150,000 and 450,000 per mm3. These limits, however, are determined by the 2.5th lower and upper percentile, and a deviation does not necessary imply any form of disease.
Signs and symptoms
Often, low platelet levels do not lead to clinical problems; rather, they are picked up on a routine full blood count. Occasionally, there may be bruising, nosebleeds and/or bleeding gums.
It is vital that a full medical history is elicited, to ensure the low platelet count is not due to a secondary process. It is also important to ensure that the other blood cell types red blood cells, and white blood cells, are not also suppressed.
Laboratory tests might include: full blood count, liver enzymes, renal function, vitamin B12 levels, folic acid levels, erythrocyte sedimentation rate.
If the cause for the low platelet count remains unclear, bone marrow biopsy is often undertaken, to differentiate whether the low platelet count is due to decreased production or peripheral destruction.
Decreased platelet counts can be due to a number of disease processes:
- decreased production
- vitamin B12 or folic acid deficiency
- leukemia or myelodysplastic syndrome
- peripheral destruction
- immune thrombocytopenic purpura (ITP)
- thrombotic thrombocytopenic purpura (TTP)
- hemolytic-uremic syndrome (HUS)
- disseminated intravascular coagulation (DIC)
- paroxysmal nocturnal hemoglobinuria
- antiphospholipid syndrome
- Many of the commonly used drugs may cause thrombocytopenia or low platelet counts. Some drugs like anticancer drugs and valproic acid causes thrombocytopenia in a dose depended mechanism by causing myelosuppression. Some other groups of drugs cause thrombocytopenia by immunological mechanisms. Based up on the mechanism immunological drug induced can be caused by two types.
- Example of the first mechanism is the quinidine group of drugs. This is caused by drug depended binding of Fab part of the pathological antibody with the platelets, causing the destruction of platelets.. Fc portion of the antibody molecule is not involved in the binding process.
- Example of the second mechanism is heparin induced thrombocytopenia (HIT). In this type the Fab portion of the pathological antibody binds to platelet factor 4 (PF4).When complexed with heparin or other drugs, the Fc portion of the antibody molecule bind to platelet receptors causing platelet activation. Since Fc portion of the antibody is bound to the platelets, they are not available to the Fc receptors of the reticulo-endothelial cells. This may explain, why severe thrombocytopenia not commonly seen in patients with HIT.
- A full list of known drugs causing thrombocytopenia is available at the linked website. Most of the elderly patients are on multiple medications and the intake of these drugs must always be considered in the differential diagnosis of thrombocytopenia.
- heparin-induced thrombocytopenia (HIT or white clot syndrome): this is a rare but serious condition that may occur in a hospitalized population especially in the cardiac units where they are exposed to large quantities of heparin. HIT may occur with a delay of 4 to 14 days after exposure to heparin. As mentioned above the heparin-PF4 antibody complex will activate the platelets, and this will lead to clotting. A term known as paradoxical thrombosis (HITT, where the last T is for thrombosis) is often used to describe this condition.
- abciximab-induced thrombocytopenia
In some tropical countries, dengue infection is a known rather common cause of thrombocytopenia associated with fever.
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