• E Rumi, F Passamonti, L Pagano, M Ammirabile, L Arcaini, C Elena, A Flagiello, R Tedesco, C Vercellati, A P Marcello, D Pietra, R Moratti, M Cazzola, and M Lazzarino.
• Division of Hematology, Fondazione IRCCS Policlinico San Matteo, University of Pavia, Pavia, Italy.
• J. Intern. Med. 2009 Feb 1; 265 (2): 266-74.

BackgroundHigh oxygen-affinity haemoglobin variants and 2,3-diphosphoglycerate (2,3-DPG) deficiency are inherited diseases generating low tissue oxygen tension and erythropoietin-driven erythrocytosis, that characterizes the clinical phenotype of patients. Level of blood p50 (the oxygen tension at which haemoglobin is 50% saturated) is used to recognize these conditions.ObjectivesTo define the clinical utility of blood p50 measurement in the diagnosis of isolated erythrocytosis.Subjects And DesignVenous blood p50 measurement was included in the diagnostic work-up of 102 consecutive patients with isolated erythrocytosis besides blood cell count, arterial oxygen saturation, serum erythropoietin measurement and screening for JAK2 mutations.SettingHaematological Outpatient Section at University Hospital.ResultsSeven patients had relative erythrocytosis. Among 95 patients with absolute erythrocytosis, 4 (4.2%) had decreased p50 level. The extended study of family members revealed a familial inheritance. Two families had haemoglobin variants already described as Haemoglobin Malmö and Haemoglobin San Diego. In one family, the proband had a new high oxygen-affinity haemoglobin variant (Haemoglobin Safi) resulting from the transversion C-->A at codon 81 of the alpha2-globin gene. In the last family, a deficiency of 2,3-DPG was found. Within the 91 patients with normal p50 values, 46 (51%) had secondary erythrocytosis, 13 (14%) polycythemia vera and 32 (35%) idiopathic erythrocytosis.ConclusionsThis study suggests that the investigation of blood p50 level may be useful to define diagnosis in patients with isolated erythrocytosis.

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