Look for mucocutaneous bleeding: gingival bleeding after brushing teeth, epistaxis, menorrhagia, metrorrhagia, and easy bruising. Also look for petichiae (non-palpable, non-blanchable) in dependent areas, like the shins and feet. These should not be on the soles of the feet as there is a thick protective layer of subcutaneous tissue. You may see them on the palate as well. Check out the photos at the bottom.
Decreased Production of platelets:
- Hypocellular bone marrow: from aplastic anemia of which there are many causes(idiopathic, radiation, chemo, medications, viruses). Other cell lines will also be decreased.
- Cellular bone marrow: myelodysplastic syndromes, leukemia
- Replacement of marrow: with primary or secondary malignancies, myelofibrosis, or granuloma (eg. TB, sarcoid).
Increased Destruction of platelets:
- Immune mediated: Idiopathic Throbocytopenia Purpura (primary), or secondary to Collagen Vascular Diseases (eg. SLE), Infections (eg. HIV, Hep C), Drugs (eg. heparin, sulfa), Lymphoproliferative diseases (CLL, lymphoma), and the Antiphospholipid Antibody Syndrome.
- Non-Immune mediated: Think about things like Disseminated Intravascular Coagulation, Thrombotic Thrombocytopenia Purpura and it's cousin the Hemolytic Uremic Syndrome, HELLP syndrome in pre-eclampsia, and malignant hypertension.
- Mostly in a large spleen.
- Very rarely, blood collected in the tube will react to a chemical (EDTA) and cause platelet clumping - this may cause 'spurious' thrombocytopenia. The platelets work just fine, they just react to the EDTA.
(petichiae to the left, and palatal petichia + gingival bleeding below)