The Red Cell Mass (RCM) Value In Polycythaemia Vera Disease In The JAK2 V617F Era
Authors: Al-Jafar Hassan A. , Aytoglu Leena M , Loutfi Issa , Al-Shemmari Iman , Alshemmari Salem H 
Published: October 2019

Introduction

In Polycythaemia Vera (PV), the RBC lineage is involved with increased haemoglobin, RBC count and haematocrit. WHO diagnostic criteria for PV are JAK2 V617F mutation and elevated red cell mass (RCM) > 25% of mean normal value. In addition, tests of marrow hypercellularity, blood erythropoietin and colony formation, are minor criteria. However, the diagnostic role of RCM test is still controversial and requires clarification. In this work, PV patients who had both an RCM study and JAK2 V617F mutation test, and routine laboratory tests, are evaluated to check if RCM was essential in the diagnostic work up for PV.

Methods

Over 2 years, 75 patients with abnormal haematocrit (men ≥ 0.50, women ≥ 0.45) had RCM and JAK2 V617F mutation tests (except JAK2 exon 12 mutation). All subjects consented to the study approved by the ethics committee. RCM was done by Cr-51 RBC radiolabeling method (no prior venesection at least 1 month). Statistical analysis involved descriptive statistics and chi-square test.

Results

There were 71 males and 4 females, mean age 46 y (range 17-75 y). Increased RCM was found in 41/75 (55%). Positive JAK2 V617F was found in 13/75 patients (17%), who also had RCM above the mean normal predicted value, however, when the WHO RCM criteria were applied, only 7/13 (54%) could be considered as having “truly” increased RCM. In the patient group with negative JAK2 V617F test, 12/28 (43%) had RCM results as per WHO criteria. There was no statistical association between presence of JAK2 V617F and the RCM values.

Conclusion

In patients with negative JAK2 V617F but with high clinical suspicion for PV and all other causes of secondary and idiopathic erythrocytosis excluded, an increase in RCM would support the diagnosis of PV (about 10 % PV cases). In patients with JAK2 positive mutation and high haematocrit but RCM below the WHO cut-off level, an increased RCM would still count to confirm the diagnosis as the current standard level seems too stringent.

References

James C, Ugo V, Le Couedic JP, Staerk J, Delhommeau F, Lacout C et al. A unique clonal JAK2 mutation leading

to constitutive signaling causes polycythaemia vera. Nature 2005; 434(7037): 1144-8.

Kralovics R, Passamonti F, Buser AS, Soon-Siong T, Tiedt R, Passweg JR, et al. A Gain-of-Function Mutation of JAK2 in Myeloproliferative Disorders. Merck Manual of Diagnosis and Therapy. 16th Edition, 1992

McMullin MF, Bareford D, Campbell P, Green AR, Claire Harrison C, Hunt B, Oscier D, et al. Guidelines for the diagnosis, investigation and management of polycythaemia/erythrocytosis. British Journal of Haematology 2005;

130(2): 174-95.

Scott LM, Tong W, Levine RL, et al. JAK2 exon 12 mutations in polycythemia vera and idiopathic erythrocytosis. N

Engl J Med. 2007;356:459-468.

Pardanani A, Lasho TL, Finke C, et al. Prevalence and clinicopathologic correlates of JAK2 exon 12 mutations in JAK2V617F-negative polycythemia vera. Leukemia. 2007;21:1960-1963.

Pancrazzi A, Guglielmelli P, Ponziani V, et al. A sensitive detection method for MPLW515L or MPLW515K mutation in chronic myeloproliferative disorders with locked nucleic acid-modified probes and real-time polymerase chain reaction. J Mol Diagn. 2008;10:435-441.

Disclosures:

No relevant conflicts of interest to declare.