The normal range for the platelet count in peripheral blood at all ages is 150-400 x 109/l. A platelet count below this level does not in itself indicate a need for platelet transfusion. Isolated thrombocytopenia, in the absence of any other abnormality, is unlikely to be complicated by serious spontaneous haemorrhage if the count remains above 5 -10 x 109/l. Recent studies indicate that the clinically stable patient is unlikely to benefit from prophylactic platelet transfusion if the count is greater than 10 x 109/l. A higher threshold for transfusion is generally advised in the presence of sepsis. However, some experts question the usefulness of the platelet count in the peripheral blood as a guide to the risk of bleeding or as a means for assessing the effect of platelet transfusion.

Clinical transfusion guidelines for platelet transfusion usually cover the management of bleeding during surgery or patients with bone marrow suppression and the prevention of bleeding in patients with low platelet count due to bone marrow suppression or other causes (PMID 19109560, 15495093, 15584985, 16351634). Some guidelines specify target platelet counts. In clinical practice the recommended target platelet counts may not be achieved even with large doses of platelets.

The following is an extract from the 2009 Guidelines of the German Medical Association

Major haemorrhage:

• Transfuse if count <50 × 109/l, or
• In multiple or CNS trauma < 100 × 109/l (recommendation level 2C)

Thrombocytopenia due to chemotherapy

• Transfuse if count <10 × 109/l if not bleeding and no other risk factors (recommendation level 1A)
• Transfuse if count <20 × 109/l if at risk due to sepsis, antibiotics, abnormal clotting (recommendation level 2C)
• Transfuse if there is evident bleeding (recommendation level 1C)

Invasive surgical procedures

• Transfuse if count <50 × 109/l: < 70-100x109 in procedures, such as neurosurgery, where bleeding carries higher risks (recommendation level 1C)

Invasive diagnostic interventions

• Guidance depends on individual procedure, patient risk factors for bleeding, and risk to patient if bleeding occurs