PB2237 THE RED BLOOD CELL COUNT AND THE SEDIMENTATION RATE IN THE DIAGNOSIS OF POLYCYTHAEMIA VERA?

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Background:This retrospective cross‐sectional study investigated the effects of microcytosis on the hematocrit (HCT) value in Polycythemia Vera (PV) patients. Since iron deficiency is frequent in PV, and the HCT is a derived value from the Red Blood cell Count x Mean Corpuscular Volume (RBC x MCV), it is reasonable to question if low MCV in PV affects the validity of the HCT value. In addition, we evaluated the Erythrocyte Sedimentation Rate (ESR) as a possible additional diagnostic marker for PV.Aims:To evaluate RBC, hematocrit and the ESR in the diagnosis of PV.Methods:This study included 182 subjects (39 with PV, 27 with Essential Thrombocythemia (ET) and 116 suspected of MPN disease with a secondary cause for either thrombocytosis or erythrocytosis (hereafter named “MPN‐suspects”). The frequencies of microcytosis and low ferritin (<15ug/L) in PV patients were compared to subjects suspected of having a MPN disease. Correlation studies were performed to compare the HCT versus RBC in all subgroups. The ESR was evaluated as a diagnostic marker for PV by a contingency table and a ROC‐curve analysis.Results:In the MPN suspects, 4 of 117 (3 %) had plasma ferritin < 15 ug/L, compared with 6 of 38 (16 %) in the PV‐group (P < 0.05). In the MPN suspects, we found that 3 of 115 (3%) as compared to 6 of 39 (15%) in the PV‐group had MCV < 82 (p < 0.05). Poor linear correlations of RBC versus HCT were found in the PV group compared to the MPN suspects (R2 = 0.62 and R2 = 0.76, respectively). When subjects with microcytosis were excluded, better correlations were observed (R2 = 0.87 in PV and R2 = 0.82 in the MPN suspect group). We found a specificity of 97,7% and a sensitivity of 37,1% for ESR < 2 mm by a ROC‐curve analysis when used for diagnosing PV when PV was suspected. The area under the curve (AUC) was 0,71 (95% CI: 0.60‐0.82), indicating a fair test accuracy for ESR as a diagnostic test.Summary/Conclusion:The HCT is not a valuable parameter in the assessment of expanded RCM in PV, since HCT is falsely lowered due to iron deficiency with microcytosis, which are common findings in patients with PV. The RBC is a simple measurement that may more precisely reflect the total red cell mass which also impacts the ESR as reflected by a low ESR (< 2 mm) in 13 of 35 (37 %) of PV patients at the time of diagnosis. Importantly, the ESR might also be a valuable diagnostic biomarker for PV with a high specificity in patients with elevated HCT, Hb or RBC. A combination of RBC and ESR as simple measures to substitute the Hb‐concentration and the HCT in the diagnosis of PV should be addressed in future well‐designed prospective studies, including the value of the RBC and the ESR in deciding when to phlebotomize patients with PV.