Table 2.

Clinical and laboratory characteristics of sickle cell disease patients according to hydroxyurea treatment

	Not on hydroxyurea		Hydroxyurea treatment		P*
	n	Result	n	Result
Age, y	247	11 (10-12)	150	13 (12-14)	<.001
Female sex, no. (%)	247	123 (50)	150	67 (45)	.3
Severe sickling phenotype, hemoglobin SS, Sβ0 thalassemia, or SDLA, no. (%)	244	171 (70)	149	127 (85)	.001
Oxygen saturation, %†	233	97 (97-98)	144	98 (98-99)	.001
Change in oxygen saturation during 6-minute walk, %†	183	0 (−1-0)	132	0 (−1-0)	.6
Tricuspid regurgitation velocity, m/s†	227	2.3 (2.2-2.3)	143	2.3 (2.2-2.3)	.5
Tricuspid regurgitation velocity, 2.5 m/s or higher, no. (%)	227	47 (21)	143	33 (23)	.6
Tricuspid regurgitation velocity, 2.6 m/s or higher, no. (%)	227	22 (10)	143	19 (13)	.3
Hemoglobin g/L†	235	91 (89-93)	147	97 (94-99)	.002
Mean corpuscular volume, fL†	230	81 (79-82)	146	92 (90-93)	<.001
White blood cells, ×109/L†	230	10.7 (10.2-11.2)	143	8.8 (8.2-9.5)	.001
Absolute neutrophil count, ×109/L	229	5.2 (4.8-5.5)	145	4.2 (3.7-4.6)	.00
Platelets, ×109/L†	230	384 (364-408)	146	361 (331-388)	.2
Reticulocytes, ×109/L†	227	240 (220-259)	146	198 (174-224)	.026
Lactate dehydrogenase, U/L†	219	403 (380-424)	136	365 (336-391)	.070
Aspartate aminotransferase, U/L†	232	42 (40-44)	149	36 (33-39)	.006
Total bilirubin, mg/dL†	232	2.4 (2.2-2.6)	149	2.0 (1.8-2.2)	.034
Hemolytic component‡	209	0.32 (0.12-0.52)	133	−0.36 (−0.63-−0.08)	.001
Hemoglobin F, %†	121	9 (7-10)	76	13 (11-15)	<.001
Hemoglobin F 8% or higher, no. (%)	121	55 (45)	76	56 (74)	<.001
Erythropoietin, IU/L§	227	48 (44-52)	143	59 (52-66)	.012

Results are mean (95% confidence interval [CI] of mean) unless otherwise indicated.

^*Comparison of patients on hydroxyurea with those not on hydroxyurea.

^†Adjusted for sickling phenotype, age, sex, site, and chronic transfusion program.

^‡Adjusted for sickling phenotype, sex, site, and chronic transfusion program.

^§Adjusted for sickling phenotype, age, sex, site, hemoglobin concentration, and chronic transfusion program.