Psychometric test scores of patients with sickle cell disease stratified by hematocrit
| Comparison | Hematocrit ≥ 27 | Hematocrit < 27 | Δ | Pooled t test P < | ||||
|---|---|---|---|---|---|---|---|---|
| No. | Mean ± SD | No. | Mean ± SD | |||||
| Mean hematocrit | 17 | 29.2 ± 3.2 | 28 | 21.4 ± 3.7 | −26.7% | 0.0001 | ||
| Full-scale IQ | 17 | 86.0 ± 13.8 | 28 | 76.9 ± 11.3 | −10.6% | 0.006 | ||
| WISC-R FSIQ | 6 | 90.5 ± 9.0 | 9 | 82.0 ± 8.1 | −9.4% | 0.04 | ||
| WISC-III FSIQ | 11 | 83.5 ± 12.4 | 19 | 74.5 ± 12.0 | −10.8% | 0.03 | ||
| Verbal IQ | 11 | 87.1 ± 12.5 | 19 | 77.1 ± 12.9 | −11.5% | 0.02 | ||
| Performance IQ | 11 | 82.7 ± 12.6 | 19 | 76.2 ± 12.2 | −7.9% | NS | ||
| WISC-III factor scores | ||||||||
| VC factor | 10 | 89.9 ± 13.4 | 19 | 77.0 ± 11.7 | −14.3% | 0.006 | ||
| PO factor | 11 | 84.0 ± 13.7 | 19 | 75.8 ± 12.9 | −9.8% | NS | ||
| FD factor | 10 | 96.2 ± 12.1 | 19 | 85.3 ± 13.3 | −11.3% | 0.02 | ||
| PS factor | 10 | 88.6 ± 11.7 | 18 | 87.7 ± 18.5 | −1.0% | NS | ||
Note.—IQ indicates intelligence quotient; WISC-R (FSIQ), Wechsler Intelligence Scales for Children-Revised full-scale intelligence quotient; WISC-III FSIQ, Wechsler Intelligence Scales for Children-Version III full-scale intelligence quotient; VC, verbal comprehension; PO, perceptual organization; FD, freedom from distractibility; PS, processing speed; NS, not significant. When hematocrit was used to partition patients into those with low hematocrit values (<27) and those with more normal hematocrit values (≥27), significant differences in psychometric test scores were observed: The Δ value was calculated as the percent reduction in the comparison value in the low hematocrit group, compared with the value in the more normal hematocrit group. A one-way pooled t test was used to test for significance because of a prediction that patients with low hematocrit would have lower psychometric test scores. Patients with low hematocrit were not significantly younger than patients with more normal hematocrit (9.6 versus 9.4 years, P = .43).