Table 1. Patient characteristics stratified by quartile of serum phosphorus.
| n | Quartile 1 2979 | Quartile 2 2947 | Quartile 3 2577 | Quartile 4 2169 | P-value |
|---|---|---|---|---|---|
| Serum phosphorus range, mg/dl | ≤3.3 | >3.3 to 3.7 | >3.7 to 4.1 | >4.1 | |
| Mean serum phosphorus, mg/dl | 3.1 ± 0.3 | 3.6 ± 0.1 | 3.9 ± 0.1 | 4.6 ± 0.5 | |
| Demographics | |||||
| Age, years | 71 ± 11 | 71 ± 10 | 71 ± 11 | 69 ± 12 | <0.0001 |
| Gender, % men | 47 | 33 | 25 | 21 | <0.0001 |
| Race/ethnicity, % | <0.0001 | ||||
| Non-Hispanic white | 66 | 66 | 68 | 65 | |
| Non-Hispanic black | 23 | 22 | 21 | 19 | |
| Hispanic, white, or black | 2 | 2 | 2 | 3 | |
| Asian | 3 | 4 | 3 | 5 | |
| Others | 5 | 6 | 6 | 7 | |
| Highest education, % | 0.49 | ||||
| Grade school or less | 6 | 6 | 6 | 6 | |
| Some high school | 11 | 12 | 11 | 11 | |
| High school graduate | 32 | 30 | 32 | 33 | |
| Some college | 23 | 24 | 24 | 24 | |
| College graduate | 16 | 15 | 15 | 15 | |
| Postgraduate or professional | 13 | 13 | 11 | 12 | |
| Barriers/access to care | |||||
| Difficulty in getting medical care, % | 0.02 | ||||
| Extremely difficult | 3 | 3 | 3 | 4 | |
| Moderately difficult | 4 | 4 | 4 | 4 | |
| Somewhat difficult | 7 | 7 | 7 | 9 | |
| Not very difficult | 21 | 21 | 20 | 22 | |
| Not difficult | 66 | 66 | 66 | 61 | |
| Health insurance available, % | 92 | 92 | 91 | 89 | <0.0001 |
| Last time made visit to doctor | 0.85 | ||||
| Within past year | 95 | 95 | 95 | 95 | |
| 1–2 years ago | 4 | 3 | 4 | 4 | |
| More than 2 years ago | 1 | 2 | 2 | 1 | |
| Awareness of CKD, % | 16 | 15 | 16 | 19 | 0.002 |
| CKD | |||||
| Serum creatinine, mg/dla | 1.3 (1.1, 1.5) | 1.3 (1.1, 1.5) | 1.2 (1.1, 1.4) | 1.3 (1.1, 1.6) | <0.0001 |
| eGFR, ml/min per 1.73m2 | 49 ± 9 | 48 ± 9 | 47 ± 10 | 44 ± 13 | <0.0001 |
| <15.0 | 0.03 | 0.07 | 0.35 | 3 | |
| 15.0–29.9 | 3 | 5 | 6 | 11 | |
| 30.0–44.9 | 25 | 26 | 28 | 29 | |
| 45.0–59.9 | 71 | 69 | 66 | 57 | |
| Albuminuria, % | |||||
| <30 mg/g | 76 | 78 | 78 | 72 | <0.001 |
| 30–300 mg/g | 21 | 19 | 18 | 20 | |
| >300 mg/g | 3 | 4 | 4 | 8 | |
| Comorbidities, % | |||||
| Diabetes mellitus | 47 | 47 | 47 | 48 | 0.67 |
| Hypertension | 94 | 94 | 93 | 94 | 0.23 |
| Current tobacco use | 4 | 5 | 6 | 7 | 0.0001 |
| Dyslipidemia | 84 | 86 | 86 | 88 | 0.0004 |
| Prevalent CVD | 44 | 44 | 42 | 46 | 0.04 |
| Body mass index, kg/m2 | 30.4 ± 6.3 | 30.2 ± 6.3 | 29.9 ± 6.4 | 29.8 ± 6.6 | 0.002 |
| Laboratory parameters | |||||
| Plasma glucose, mg/dla | 112 (97, 144) | 108 (95, 133) | 107 (95, 131) | 107 (95, 133) | <0.0001 |
| Serum calcium, mg/dl | 9.6 ± 0.5 | 9.7 ± 0.5 | 9.7 ± 0.5 | 9.7 ± 0.5 | 0.001 |
| Serum PTH, pg/mla | 73 (49, 109) | 68 (45, 100) | 67 (46, 99) | 64 (42, 100) | <0.0001 |
| Hemoglobin, g/dl | 13.5 ± 1.5 | 13.3 ± 1.5 | 13.1 ± 1.4 | 12.9± 1.6 | <0.0001 |
Abbreviations: CKD, chronic kidney disease; CVD, cardiovascular disease; eGFR, estimated glomerular filtration rate; PTH, parathyroid hormone.
a
Data presented as median with 25th and 75th percentiles.