Table I.

Characteristics of the Patients at Base Line, According to Cumulative Hydroxyurea Exposure. Baseline rows show values obtained prior to randomization to receive hydroxyurea or a placebo. Columns shw the cumulative hydroxyurea use.

Characteristic	Never (1)	Yrs<5 (2)	5<=yrs<10 (3)	10<=yrs<15 (4)	Yrs>=15 (5)	p-value *
	N=44	N=140	N=55	N=40	N=20
Age
<20	4 (9.1)	10 (7.1)	5 (9.1)	2 (5.0)	0	0.4792
20<=age<30	24 (54.5)	60 (42.9)	25 (45.5)	13 (32.5)	10 (50.0)
30<=age<40	12 (27.3)	56 (40.0)	17 (30.9)	21 (52.5)	9 (45.0)
40<=age<50	2 (4.5)	13 (9.3)	6 (10.9)	4 (10.0)	1 (5.0)
50<=age<60	2 (4.5)	1 (0.7)	2 (3.6)	0	0
Gender
Male	21 (47.7)	61 (43.6)	33 (60.0)	20 (50.0)	11 (55.0)	0.1871
Female	23 (52.3)	79 (56.4)	22 (40.0)	20 (50.0)	9 (45.0)
No. of crises in the year before study entry (n, % of patients)
3-5	22 (50.0)	53 (37.8)	22 (40.0)	20 (50.0)	11 (55.0)	0.6557
6-9	13 (29.5)	35 (25.0)	13 (23.6)	9 (22.5)	4 (20.0)
>=10	9 (20.4)	52 (37.1)	20 (36.4)	11 (27.5)	5 (25.0)
Complications of sickle cell anemia (n,% of patients)
Chest syndrome	29 (65.9)	97 (69.3)	34 (61.8)	20 (50.0)	15 (75.0)	0.2626
Ankle ulcer	12 (27.3)	43 (30.7)	17 (30.9)	13 (32.5)	2 (10.0)	0.6387
Aseptic necrosis of bone	9 (20.4)	34 (24.3)	13 (23.6)	5 (12.5)	2 (10.0)	0.2082
Mean reported for lab parameters						Pair-wise comparison significant at the 0.05 level #
Hemoglobin (g/dl)	8.5	8.4	8.6	8.3	9.3	1-5 2-5 3-5 4-5
MCV (μm3)	92.2	93.2	93.7	93.0	96.4	None
WBC (10-3/mm3)	12.0	12.2	13.5	12.0	12.6	1-3 2-3 3-4
Platelets (10-3/mm3)	492.4	463.1	476.1	501.3	487.4	None
Reticulocytes (10-3/mm3)	319.3	309.4	351.0	341.2	354.2	2-3 2-5
Fetal Hemoglobin (%)	5.9	4.5	5.3	5.3	6.0	1-2
F cells (%)	35.1	29.6	35.2	34.1	35.9	2-3
Dense cells (%)	15.3	14.2	13.1	12.7	13.5	None

^*p-value (2-sided) determined by the Kruskal-Wallis test

^#p-value (2-sided) determined by least significant difference; ANOVA.