Marrow cellularity in the diagnosis of polycythaemia.

Increased marrow cellularity is well recognised in polycythaemia rubra vera (PRV), but its value in the differential diagnosis of polycythaemia is not always appreciated. In 28 patients who had marrow aspiration performed on account of a raised haemoglobin concentration or red blood cell count (RBC), marrow cellularity was assessed subjectively and also measured; a comparison was made with the white blood cell count (WBC), platelet count, presence of splenomegaly and plasma volume (PV). Marrow cellularity, particularly when measured was shown to be the most reliable method of making a positive diagnosis of polycythaemia vera; cellularity of greater than 75% makes it unnecessary to perform other investigations to exclude secondary erythrocytosis.