Table 1. Clinical and laboratory features at diagnosis of 132 patients with prefibrotic myelofibrosis compared with those with primary myelofibrosis-fibrotic type.

	Myelofibrosis-fibrotic type	Prefibrotic myelofibrosis	P§	Myelofibrosis-fibrotic type with BM fibrosis grade 1	P§§	Myelofibrosis-fibrotic type with BM fibrosis grade 2 or 3	P§§§
Number	551	132		206		345
Percentage (95% CI)	80.7 (77.6–83.7)	19.3 (16.3–22.4)		30.2 (26.8–33.8)		50.5 (46.8–54.4)
Demographics
Female, number (%)	184 (33.4)	79 (60.3)	0.001	87 (42.2)	0.021	97 (28.1)	0.046
Age at onset of the disease, years, mean (range)	54.9 (6–90)	38.3 (6–73)	<0.001	50.9 (6–80)	<0.001	57.4 (11–90)	<0.001
Laboratory and Clinical features at diagnosis
Hemoglobin, g/L; mean (range)	11.9 (3–19.6)	14.2 (10–20.4)	<0.001	13.3 (4.6–19.6)	0.001	11.1 (3–19)	<0.001
WBC count, ×109/L; mean (range)*	10.6 (1.5–64.3)	9.2 (2.5–31.5)	0.043	11.5 (2.2–50.9)	0.001	10.1 (1.5–64.3)	0.043
Plt count, ×109/L; mean, (range)	432 (5–2926)	647 (115–2700)	<0.001	553 (19–1860)	0.013	359 (5–2926)	<0.001
Spleen index, cm2; mean (range)**	181 (70–1200)	118 (80–315)	<0.001	152 (70–627)	<0.001	199 (80–1200)	<0.001

^§P value refers to the difference between prefibrotic myelofibrosis and myelofibrosis-fibrotic type;

^§§P value refers to the difference between prefibrotic myelofibrosis and myelofibrosis-fibrotic type with bone marrow (BM) fibrosis grade 1;

^§§§P value refers to the difference between myelofibrosis-fibrotic type with BM fibrosis grade 1 and with BM fibrosis grade 2 or 3;

^*White-blood cell (WBC) count was corrected for the number of circulating erythroblasts;

^**Spleen index is the product of the longitudinal by the transverse spleen axis, the latter defined as the maximal width of the organ.