Thrombocytosis

 Q: How a simple blood smear can help to make a differential diagnosis in thrombocytosis?

Answer: The size/shape of the platelets on the simple blood smear can quickly guide clinicians towards the cause of persistent thrombocytosis (a common condition encountered in ICU).

If platelets are seen equivalent to RBC sizes - it is probably due to a myeloproliferative neoplasm (PMN). In contrast, young platelets are a sign of a reactive process or a familial disorder. 

Again, platelets larger than RBCs, called giant platelets - and/or - conglomerates of platelets, bizarre shapes, megakaryocytic fragments, hypogranular platelet - are seen with PMN or familial disorders. This is unlikely in reactive thrombocytosis.

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References:

1. Greinacher A, Pecci A, Kunishima S, Althaus K, Nurden P, Balduini CL, Bakchoul T. Diagnosis of inherited platelet disorders on a blood smear: a tool to facilitate worldwide diagnosis of platelet disorders. J Thromb Haemost. 2017 Jul;15(7):1511-1521. doi: 10.1111/jth.13729. Epub 2017 Jun 4. PMID: 28457011.

2. Adewoyin AS, Nwogoh B. Peripheral blood film - a review. Ann Ib Postgrad Med. 2014;12(2):71-79.

3. Bleeker JS, Hogan WJ. Thrombocytosis: diagnostic evaluation, thrombotic risk stratification, and risk-based management strategies. Thrombosis. 2011;2011:536062. doi:10.1155/2011/536062