Linear regression analysis of clinical, laboratory, and sleep study variables against pain rate (number of pain days per years of follow-up)
| Risk factors for painful crises . | Baseline characteristics . | Mean pain rate (SD) . | Coefficient* . | 95% confidence interval . | P . | ||
|---|---|---|---|---|---|---|---|
| No. . | Mean . | Range . | |||||
| Age at sleep study, y | 95 | 8.2 | 2.1-16.9 | — | 0.07 | −0.13, 0.28 | .46 |
| Sex | |||||||
| Male | 54 (57%) | 2.95 (3.78) | 0.02 | −1.6, 1.6 | .98 | ||
| Compared to Female | 41 (43%) | 2.93 (3.85) | — | — | — | ||
| Sickle type | |||||||
| SS | 74 (78%) | 3.54 (4.08) | |||||
| Compared to SC | 14 (15%) | 0.79 (0.74) | 2.75 | 0.6, 4.9 | .01 | ||
| Sβthal, compared to SC | 7 (7%) | 0.89 (1.08) | 0.1 | −3.2, 3.5 | .95 | ||
| Dactylitis less than 1 y | |||||||
| Yes | 23 (24%) | 4.44 (2.94) | 1.6 | −0.4, 3.6 | .11 | ||
| No | 72 (76%) | 2.85 (4.35) | — | — | — | ||
| Baseline Hb level, g/dL | 95 | 8.8 | 6.3-13.3 | — | −0.6 | −1.0, −0.1 | .01 |
| Baseline Hct | 79 | 0.28 | 0.20-0.42 | — | −23.72 | −37.8, −9.64 | .0012 |
| Mean Hb level at 11 to 25 mo, g/dL | 95 | 9.1 | 6.0-12.1 | — | −0.5 | −1.2, 0.2 | .14 |
| Mean WBC at 11 to 25 mo, × 109/L | 95 | 12.1 | 0.4-25.0 | — | 0.1 | −0.6, 0.3 | .19 |
| Baseline HbF level, % | 95 | 6.9 | 0.2-21.8 | — | −0.09 | −0.3, 0.09 | .32 |
| Mean nocturnal oxygen saturation | 95 | 95.1 | 85.0-99.7 | — | −0.8 | −0.6, −0.9 | < .0001 |
| % of sleep study where oxygen saturation was less than 80% | 95 | 0.6 | 0-25.0 | — | 0.7 | 0.5, 0.9 | < .0001 |
| % of sleep study where oxygen saturation was less than 90% | 95 | 11.1 | 0-99.6 | — | 0.09 | 0.06, 0.1 | < .0001 |
| Minimum SaO2, % | 95 | 81.2 | 41-97.0 | — | −0.1 | −0.2, −0.04 | .004 |
| Normal sleep study† | 64 (67%) | 1.94 (2.77) | — | — | — | ||
| Dips on sleep study | 24 (25%) | 8.24 (4.30) | 1.4 | −0.01, 2.83 | .05 | ||
| Risk factors for painful crises . | Baseline characteristics . | Mean pain rate (SD) . | Coefficient* . | 95% confidence interval . | P . | ||
|---|---|---|---|---|---|---|---|
| No. . | Mean . | Range . | |||||
| Age at sleep study, y | 95 | 8.2 | 2.1-16.9 | — | 0.07 | −0.13, 0.28 | .46 |
| Sex | |||||||
| Male | 54 (57%) | 2.95 (3.78) | 0.02 | −1.6, 1.6 | .98 | ||
| Compared to Female | 41 (43%) | 2.93 (3.85) | — | — | — | ||
| Sickle type | |||||||
| SS | 74 (78%) | 3.54 (4.08) | |||||
| Compared to SC | 14 (15%) | 0.79 (0.74) | 2.75 | 0.6, 4.9 | .01 | ||
| Sβthal, compared to SC | 7 (7%) | 0.89 (1.08) | 0.1 | −3.2, 3.5 | .95 | ||
| Dactylitis less than 1 y | |||||||
| Yes | 23 (24%) | 4.44 (2.94) | 1.6 | −0.4, 3.6 | .11 | ||
| No | 72 (76%) | 2.85 (4.35) | — | — | — | ||
| Baseline Hb level, g/dL | 95 | 8.8 | 6.3-13.3 | — | −0.6 | −1.0, −0.1 | .01 |
| Baseline Hct | 79 | 0.28 | 0.20-0.42 | — | −23.72 | −37.8, −9.64 | .0012 |
| Mean Hb level at 11 to 25 mo, g/dL | 95 | 9.1 | 6.0-12.1 | — | −0.5 | −1.2, 0.2 | .14 |
| Mean WBC at 11 to 25 mo, × 109/L | 95 | 12.1 | 0.4-25.0 | — | 0.1 | −0.6, 0.3 | .19 |
| Baseline HbF level, % | 95 | 6.9 | 0.2-21.8 | — | −0.09 | −0.3, 0.09 | .32 |
| Mean nocturnal oxygen saturation | 95 | 95.1 | 85.0-99.7 | — | −0.8 | −0.6, −0.9 | < .0001 |
| % of sleep study where oxygen saturation was less than 80% | 95 | 0.6 | 0-25.0 | — | 0.7 | 0.5, 0.9 | < .0001 |
| % of sleep study where oxygen saturation was less than 90% | 95 | 11.1 | 0-99.6 | — | 0.09 | 0.06, 0.1 | < .0001 |
| Minimum SaO2, % | 95 | 81.2 | 41-97.0 | — | −0.1 | −0.2, −0.04 | .004 |
| Normal sleep study† | 64 (67%) | 1.94 (2.77) | — | — | — | ||
| Dips on sleep study | 24 (25%) | 8.24 (4.30) | 1.4 | −0.01, 2.83 | .05 | ||
SS indicates homozygous sickle; SC, hemoglobin SC; Sβthal, sickle β thalassemia; Hb, hemoglobin; Hct, hematocrit; WBC, white blood cell count; —, not applicable.
Average change in number of days of pain per year between categories or, for continuous measurements, per unit increase in the risk factor.
Seven cases with no dips but low baseline oxygen saturation were excluded from the normal sleep study group.