The Utility of V617F JAK2 Analysis for Patients with Erythrocytosis or Thrombocytosis in the General Hospital.

We performed a retrospective analysis of the diagnostic value of V617F JAK2 testing in 312 consecutive patients referred to the Royal Bournemouth Hospital over a 43 month period for investigation of erythrocytosis(n=247) or thrombocytosis (n=65). Clinical evaluation, FBC, ESR (in thrombocytosis cases) and examination of a blood film were performed in all cases. Erythrocytosis and thrombocytosis were transient in 71 and 8 patients respectively and few additional investigations were performed in these cases. Abdominal ultrasonography was performed in 187 patients; serum EPO was measured in 130 patients and bone marrow examination was performed in 30. Based on this data, patients with a persistent erythrocytosis were initially classified as having a secondary cause, predominantly heavy smoking +/− high alcohol intake (n=89), features of P Vera, including 4 with presenting iron deficiency (n= 19) or no obvious cause (n=68). Red cell mass and plasma volume estimation was only sporadically available, and was performed in 63 patients with either a secondary or no obvious cause for erythrocytosis. Only 11/63 had a true erythrocytois. Marrow examination was undertaken in 38 cases with thrombocytosis. Persistent thrombocytosis cases were classified as primary thrombocythaemia (PT) (n=35), reactive (n=5), idiopathic (n=5) or CML (n=1).

Peripheral blood leucocytes were subsequently screened for the V167F mutation using allele specific PCR and pyrosequencing. This test was offered to all 304 live patients. Results are available on 136 erythrocytosis patients (81% of patients with regular haematology follow up and 32% of discharged cases) and 42 thrombocytosis patients. (90% with follow up and 21% of discharges)

Table 1 shows the incidence of V617F mutations among patients with erythrocytosis grouped according to the original diagnosis. Marrow examination in the one V617F-ve case of P Vera was consistent with an MPD. The diagnostic yield of V617F screening in patients not suspected of having P Vera was low. A low seum Epo was a poor predictor of either a JAK2 mutation or a diagnosis of P Vera. Only 2/187 abdominal US scans provided a clinically important diagnosis unsuspected from other investigations. No additional cause for erythrocytosis was found in patients who smoked heavily. Heterozygous V617F was found in 22/33 patients clinically diagnosed as PT, including 3/4 whose platelet count was <600×10⁹/l and in 0/10 patients with other causes of thrombocytosis. V617F was detected in 10/19 patients whose marrow was consistent with PT and in 3/5 patients with suspected PT whose marrows were considered normal or technically unsatisfactory.

In summary a combination of better defined criteria for haematology referral and early screening of selected patients for the V617F mutation, based on clinical evaluation, and the results of an FBC, ESR and blood film, can provide a rapid diagnosis for the majority of patients with P Vera and PT and reduce the need for additional investigations.