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5017 Diagnostic Accuracy of Erythropoietin and Jakpot in Predicting JAK2-Postiive Erythrocytosis: A Retrospective Cohort Study

Program: Oral and Poster Abstracts
Session: 901. Health Services and Quality Improvement: Non-Malignant Conditions Excluding Hemoglobinopathies: Poster III
Hematology Disease Topics & Pathways:
Clinical Practice (Health Services and Quality)
Monday, December 9, 2024, 6:00 PM-8:00 PM

Justin Senecal, MD, BSc1*, Yasmine Madan2*, Sabina Rajkumar3*, Rabia Tahir2*, Mark A. Crowther, MD, MSc, FRSC, FRCPC, LLM1,4 and Siraj Mithoowani, MD FRCPC5

1Department of Medicine, McMaster University, Hamilton, ON, Canada
2McMaster University, Hamilton, ON, Canada
3McMaster University, Hamilton, Canada
4Department of Medicine, McMaster University, Hamilton, Canada
5McMaster University, Hamilton, ON, CAN

Introduction:

Erythrocytosis affects 0.5 – 4% of ambulatory patients and is a common reason for Hematology referral. Very few patients are ultimately diagnosed with a myeloproliferative neoplasm such as polycythemia vera. The JAKPOT score (Chin-Yee et al) incorporating platelet, neutrophil, and erythrocyte counts shows promise at identifying patients at low risk of JAK2-positive erythrocytosis, but has not been externally validated. Our aim was to compare the diagnostic accuracy of serum erythropoietin (EPO) with the JAKPOT score to identify patients with JAK2-positive erythrocytosis.

Methods:

Retrospective cohort study including all patients who had EPO and JAK2 molecular testing (V617F or exon 12) for undifferentiated erythrocytosis at a tertiary care centre in Hamilton, Canada between Dec. 2014 – Dec. 2022. Patients with hemoglobin < 125 g/L were excluded. Demographics, comorbidities, medications, and laboratory parameters were collected. Univariate analysis to detect predictors of JAK2 positivity was performed with Mann Whitney U-tests, two-tailed Welch t-tests and Chi-squared tests where appropriate. Multivariate logistic regression analysis was performed with a subset of the predictors. We determined the sensitivity (Sn), specificity (Sp), positive and negative likelihood ratios (+LR, -LR) of EPO, JAKPOT score, and a combination of serum EPO and JAKPOT (EPO-JAKPOT) to diagnose JAK2-positive erythrocytosis.

Results:

The initial cohort included 237 patients (74 female, mean age 57.7 years). Twenty-four (10%) patients were excluded because they were known to have donated blood or had been phlebotomized in the 3 months preceding laboratory investigation, leaving 213 patients for analysis.

The mean hemoglobin and hematocrit were 174 g/L and 0.52 L/L respectively. Forty patients (19%) had positive JAK2 molecular testing. Multivariate logistic regression showed that increasing age (p=0.001), increasing platelet count (p=0.006), decreasing serum ferritin (p=0.018) and low EPO (< 3.8 mU/mL) (p<0.001) were associated with JAK2-positive erythrocytosis, while the other components of the JAKPOT score, neutrophils (p=0.292) and erythrocytes (p=0.670), were not.

Low EPO had a Sn of 0.77 (95% CI, 0.62 – 0.87), Sp of 0.98 (95% CI, 0.94 – 0.99), +LR of 33 and -LR of 0.23 for the diagnosis of JAK2-positive erythrocytosis. A positive JAKPOT score had a Sn of 0.88 (95% CI, 0.73 – 0.94), Sp of 0.65 (95% CI, 0.57 – 0.72), +LR of 2.5 and -LR of 0.19 to diagnose JAK2-positive erythrocytosis. A JAKPOT score ≥ 1 or low EPO (EPO-JAKPOT+) had a Sn of 0.95 (95% CI, 0.83 – 0.98), Sp of 0.65 (95% CI, 0.58 – 0.72), +LR of 2.7 and -LR of 0.07. Restricting JAK2 testing to patients who were EPO-JAKPOT+ would have led to 55% fewer molecular tests in our cohort but would have missed 2 (5%) of JAK2+ patients.

Conclusions:

Individually, low EPO and the JAKPOT score had modest sensitivity for JAK2-positive erythrocytosis. Combining EPO and JAKPOT into the EPO-JAKPOT score increased the sensitivity to 95% and had a -LR of 0.07. While further validation is needed, this score has the potential to lessen molecular testing for erythrocytosis by identifying a population at low risk of disease.

Disclosures: Crowther: Bayer: Other: In the last 36 months, Dr. Crowther has received Personal Funding, including but not limited to preparation of educational material, participation in Advisory Boards, or providing expert testimony; AstraZeneca: Other: In the last 36 months, Dr. Crowther has received Personal Funding, including but not limited to preparation of educational material, participation in Advisory Boards, or providing expert testimony; Pfizer: Other: In the last 36 months, Dr. Crowther has received Personal Funding, including but not limited to preparation of educational material, participation in Advisory Boards, or providing expert testimony; Hemostasis Reference Laboratories: Other: In the last 36 months, Dr. Crowther has received Personal Funding, including but not limited to preparation of educational material, participation in Advisory Boards, or providing expert testimony; Syneos Health: Other: In the last 36 months, Dr. Crowther has received Personal Funding, including but not limited to preparation of educational material, participation in Advisory Boards, or providing expert testimony; Eversana: Other: In the last 36 months, Dr. Crowther has received Personal Funding, including but not limited to preparation of educational material, participation in Advisory Boards, or providing expert testimony. Mithoowani: UpToDate: Other: Authorship Royalties.

*signifies non-member of ASH