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Distinguishing ET JAK2V617F from PV
For patients with either ETJAK2V617F or PV, the HCT values overlap in 36.0% of men and 25.0% of women (Figure 2A), the HGB values overlap in 40.0% of men and 54.7% of women (Figure 2B), and the RBC values overlap in 44.0% of men and 35.9% of women (data not shown). In these fig- ures, the threshold values are shown in vertical, solid lines.
Querying our outpatient and inpatient electronic med- ical records with a bioinformatics tool provisioned by WCM showed that of 410 presumptive PV patients, 199 (48.5%) and 225 (54.9%) had a marrow biopsy performed and a SEV measured, respectively.
Discussion
For more than half a century, it has been emphasized that a single HCT or HGB determination cannot be used as a surrogate for RCM.4,10,11 Additional errors in blood count values are compounded by poor techniques of obtaining blood samples and other issues affecting plasma volume. We attempt to minimize these errors by collect- ing blood samples at the same time of the day insofar as possible and by using a standardized blood collection technique.12 To attain an accurate RCM and plasma vol- ume, we employ a dual isotope technique, using Cr-51 and I135 to measure these values simultaneously. In this study, as expected, the plasma volume was increased in PV.4,10 We have no explanation for the gender differences, but insights may be learned from a larger sample size. The normal RCM and reduced plasma volume found in ETJAK2V617F patients accounted for the increased red cell val- ues at the time of diagnosis.
An insufficient number of matched Cr-51 RCM and marrow results from our patients precluded comparison or correlation, which we plan to carry out as a future study. Discriminating ETJAK2V617F from PV is hierarchal with a dual isotope RCM study remaining the “gold standard”. We recognize that many institutions cannot perform the standard dual isotope technique;13 in this situation, we espouse the use of marrow biopsy, which is now per- formed in all potential MPN patients at our institution at diagnosis, even in patients with a measured Cr-51 RCM to evaluate baseline fibrosis and cellularity to assess subse- quent response to treatment.14 It would be of interest to correlate marrow biopsy and Cr-51 RCM findings in the future. Despite the usefulness of a diagnostic marrow findings, as reported by us and others,4,8 such findings have not been universally accepted15-17 and even the value of marrow examination in general has been questioned.18
Although the SEV is a WHO 2016 minor criterion for the diagnosis of PV,6 we emphasize that approximately 15% of PV patients have a normal SEV (4-27 mU/mL).19,20 This fact and the availability of isotope studies may account for the relatively infrequent use of this test at our institution in the past. However, this laboratory value may be used in combination with abnormal red cell values to distinguish ETJAK2V617F from PV with higher accuracy than using red cell values exclusively.
There are no published data regarding the frequency with which marrow biopsy and SEV are currently per- formed in patients with PV at diagnosis by general hema- tologists. We reviewed marrow performance at our insti- tution over the past decade and found that marrow biop- sies were performed in 199 of 410 (48.5%) and an SEV
ABC
Figure 2. Frequencies of red cell values in men and women with polycythemia vera (PV) (dotted curve) and essential thrombocythemia (ETJAK2V617F) (dashed curve). Proposed thresholds shown in black, vertical line. (A) For hematocrit (HCT), (B) for hemoglobin (HGB), and (C) for red blood cells (RBC).
haematologica | 2019; 104(11)
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