Table 2. Characteristics of the study population by categories of urine specific gravity levels in NHANES 2007−2008.
| Characteristic | Urine specific gravity (g/mL) | P value | ||
|---|---|---|---|---|
| <1.008 | 1.008–1.020 | >1.020 | ||
| Total patients | 506 | 2,710 | 1,575 | |
| Gender | <0.001 | |||
| Male | 156 (30.8) | 1,265 (46.7) | 952 (60.4) | |
| Female | 350 (69.2) | 1,445 (53.3) | 623 (39.6) | |
| Age, years | <0.001 | |||
| 20–39 | 132 (26.1) | 774 (28.6) | 644 (40.9) | |
| 40–59 | 183 (36.2) | 852 (31.4) | 550 (34.9) | |
| 60+ | 191 (37.7) | 1,084 (40.0) | 381 (24.2) | |
| Race | <0.001 | |||
| Non-Hispanic white | 315 (62.3) | 1,339 (49.4) | 593 (37.7) | |
| Non-Hispanic black | 49 (9.7) | 523 (19.3) | 379 (24.1) | |
| Mexican American | 75 (14.8) | 454 (16.8) | 323 (20.5) | |
| Other Hispanic | 44 (8.7) | 277 (10.2) | 217 (13.8) | |
| Others | 23 (4.5) | 117 (4.3) | 63 (4.0) | |
| Marital status | 0.001 | |||
| Married | 290 (57.3) | 1,477 (54.5) | 819 (52.0) | |
| Unmarried | 186 (36.8) | 1,066 (39.3) | 609 (38.7) | |
| Other | 30 (5.9) | 167 (6.2) | 147 (9.3) | |
| Education | 0.935 | |||
| Less than high school | 153 (30.2) | 816 (30.1) | 489 (31.0) | |
| High school or equivalent | 120 (23.7) | 686 (25.3) | 378 (24.0) | |
| College or above | 233 (46.0) | 1,206 (44.5) | 707 (44.9) | |
| Other | 0 (0.0) | 2 (0.1) | 1 (0.1) | |
| Hypertension | <0.001 | |||
| Yes | 174 (34.4) | 1,031 (38.0) | 474 (30.1) | |
| No/unknown | 332 (65.6) | 1,679 (62.0) | 1,101 (69.9) | |
| Diabetes | 0.002 | |||
| Yes | 38 (7.5) | 348 (12.8) | 206 (13.1) | |
| No/unknown | 468 (92.5) | 2,362 (87.2) | 1,369 (86.9) | |
| BMI (kg/m2) | <0.001 | |||
| Normal (<25.0) | 209 (41.3) | 826 (30.5) | 346 (22.0) | |
| Overweight (25.0–29.9) | 180 (35.6) | 942 (34.8) | 537 (34.1) | |
| Obese (≥30.0) | 117 (23.1) | 942 (34.8) | 692 (43.9) | |
| eGFR (mL/min/1.73 m2) | <0.001 | |||
| <90 | 193 (38.1) | 1,234 (45.5) | 495 (31.4) | |
| ≥90 | 313 (61.9) | 1,476 (54.5) | 1,080 (68.6) | |
| Kidney stone | 0.026 | |||
| Yes | 35 (6.9) | 257 (9.5) | 172 (10.9) | |
| No | 471 (93.1) | 2,453 (90.5) | 1,403 (89.1) | |
| Urine albumin (μg/mL) | 27.63±128.37 | 49.69±305.64 | 48.38±332.35 | 0.048 |
| Urine creatinine (μmg/dL) | 84.45±66.10 | 119.75±62.95 | 158.70±82.24 | <0.001 |
For continuous variables, the t-test for slope was used in generalized linear models. BMI, body mass index; eGFR, estimated glomerular filtration rate.