Thrombocytopenia (low platelets)

Thrombocytopenia means the number of platelets in the blood is low. Platelets are the small cell fragments that clump together to plug damaged blood vessels and start clotting, so a low count makes bleeding and bruising more likely. The causes fall into three broad groups. First, the bone marrow makes too few — from marrow disorders, some cancers and their treatments (chemotherapy), certain infections, alcohol, or vitamin B12 or folate deficiency. Second, platelets are destroyed or used up too fast — as in immune thrombocytopenia (ITP, where the immune system attacks platelets), some infections, certain medications, or serious conditions like disseminated intravascular coagulation. Third, platelets are pooled in an enlarged spleen, often from liver disease. A low platelet count can also be a false reading from clumping in the test tube, which is checked before acting on it. The bleeding risk depends heavily on how low the count is: a mildly low count often causes no symptoms, while a very low count can cause spontaneous bruising, a pinpoint rash (petechiae), and, at extreme lows, serious bleeding. Symptoms and the underlying cause guide how urgently it is investigated.

• Platelet count — low; the degree guides the bleeding risk and urgency.
• A blood film — checks the platelets are truly low (not clumped) and looks at their appearance.
• Full blood count (haemoglobin, white cells) — whether other cell lines are affected points to the cause.
• Mean platelet volume (MPV) — can hint at whether the marrow is producing or platelets are being destroyed.
• Clotting tests — in suspected consumption (e.g. DIC).
• B12, folate, liver and infection tests — for specific causes.

• Often none, if only mildly low
• Easy or excessive bruising
• Small red or purple pinpoint spots on the skin (petechiae)
• Bleeding gums, frequent nosebleeds
• Heavy or prolonged menstrual periods
• Prolonged bleeding from cuts
• In severe cases: blood in urine or stool, or serious spontaneous bleeding