The red blood cell count and the erythrocyte sedimentation rate in the diagnosis of polycythaemia vera.

BACKGROUND: Iron deficiency in polycythaemia vera (PV) may impact the validity of the haematocrit (HCT), since HCT is red blood cell count (RBC) × mean corpuscular volume (MCV).

OBJECTIVES: To investigate (a) the effect of microcytosis on HCT, (b) the erythrocyte sedimentation rate (ESR) as a possible additional diagnostic marker for PV.

MATERIAL AND METHODS: This study included 182 subjects: 39 with PV, 27 with essential thrombocythemia (ET) and 116 suspected of myeloproliferative neoplasm (MPN) with a secondary cause for either thrombocytosis or erythrocytosis.

RESULTS: Patients with PV had significantly lower ratio of MCV and serum ferritin compared to MPN suspects. A good correlation of RBC versus HCT was found for PV and MPN subjects when individuals with microcytosis were excluded (R2  = .87 in PV and R2  = .82 in MPN suspects). We found a specificity of 98% and a sensitivity of 37% for ESR <2 mm in the diagnosis of PV.

CONCLUSION: The RBC may more precisely reflect the total red cell mass and accordingly the hypercoagulable state of the PV patient, which is integrated in the ESR. A combination of RBC and ESR is proposed as a novel tool to substitute the Hb concentration and the HCT in the diagnosis of PV.