An Approach to the Investigation of Thrombocytosis: Differentiating between Essential Thrombocythemia and Secondary Thrombocytosis

Table 1

Baseline characteristics, clinical risk factors for thrombocytosis, and myeloid NGS result.

Characteristics of cohort	Secondary thrombocytosis N = 160	Essential thrombocythemia (ET) N = 176	value
Age (years; mean ± SD)	56 ± 17	69 ± 15	<0.0001
Gender: male (%), female (%)	28 (18.5), 132 (82.5)	65 (36.9), 111 (63.1)
BMI (kg/m^2; mean ± SD)	30 ± 8.3	27 ± 5.4	<0.0003
WBC (×10^9 cells/L; mean ± SD)	13.2 ± 11.9	9.4 ± 4.1	<0.0001
Hemoglobin (g/L; mean ± SD)	122.9 ± 21.9	131.8 ± 17.8	<0.0001
MCV (fL; mean ± SD)	87.7 ± 7.8	90.41 ± 9.236^a	0.0049
RDW (%; mean ± SD), (N = 145, 152)	15.3 ± 2.5	15.5 ± 2.5	0.3710
MPV (fL; mean ± SD)	9.2 ± 0.9	9.6 ± 1.1	<0.0004
Platelet count (×10^9 cells/L; mean ± SD)	562 ± 141	803 ± 284	<0.0001
Change in platelet count (×10^9 cells/L; mean ± SD)	87 ± 223	−226 ± 350	<0.0001
ANC (×10^9 cells/µL; mean ± SD)	8.2 ± 7.3	6.5 ± 3.4	0.0058
Ferritin (μg/L; mean ± SD)	172 ± 320	148 ± 154	0.4522
Clinical risk factors for thrombocytosis
Smoking, n (%)	68 (53)	65 (37)	0.2113
Arterial, venous thrombosis, n (%)	16 (10), 5 (3)	39 (22), 9 (5)	0.0026, 0.3623
Prior splenectomy, n (%)	10 (63)	3 (1.7)	0.0310
Active malignancy, n (%)	11 (6.9)	4 (2.3)	0.0413
Chronic inflammatory disease, n (%)	19 (11.9)	7 (4.0)	0.0068
Iron deficiency anemia, n (%)	25 (15.6)	12 (6.8)	0.0100
Myeloid NGS results
JAK2 V617F; CALR Type 1 and Type 2; MPL	NA	95 (54), 31 (18), 20 (11), 16 (9),
Triple negative, n (%)	NA	9 (5)
Other myeloid mutations, n (%)	15 (9.7)	29 (16.5)	0.0539
	ASXL1, 3 (1.9)	TET2, 7 (4.0)
	DNMT3A, 7 (4.4)	ASXL1, 5 (2.8)
	Other 5 (3.1)	SF3B1, 5 (2.8)
		Other 12 (6.8)

Age was determined at the time of NGS testing. Change in platelet count included a total of 75 patients (23 in the ET group and 52 in the secondary thrombocytosis group) with evaluable data and excludes any patients on cytoreductive therapy. Patients may have multiple secondary causes. Some patients may have multiple mutations (3 patients in the secondary thrombocytosis had multiple mutations and 25 patients in the ET group had a second mutation alongside their driver mutation). ^aMCV was calculated on the 159 patients not on any cytoreductive therapy at the time of NGS testing (17 patients were on hydroxyurea). BMI, body mass index; WBC, white blood cells; MCV, mean corpuscular volume; RDW, red cell distribution width; MPV, mean platelet volume; ANC, neutrophil count; JAK2, Janus Kinase 2 gene; CALR, Calreticulin gene; MPL, thrombopoietin receptor protein gene.