Table 2.
Baseline Characteristics of Model Validation Cohort, Overall and by Outpatient Acute Kidney Injury
| Baseline Characteristic | All Patients (N = 4,864,576) | With Outpatient AKIa (N = 115,744) | Without Outpatient AKIa (N = 4,748,832) | P valueb |
|---|---|---|---|---|
| Age, y, median (IQR) | 63.3 (52.4-70.2) | 63.9 (56.8-70.6) | 63.2 (52.3-70.2) | <0.001 |
| Male, N (%) | 4,492,178 (92%) | 106,449 (92%) | 4,385,729 (92%) | <0.001 |
| Black, N (%) | 815,167 (17%) | 23,457 (20%) | 791,710 (17%) | <0.001 |
| Ever smoker, N (%) | 3,466,441 (71%) | 90,231 (78%) | 3,376,210 (71%) | <0.001 |
| Final creatinine of the baseline period, mg/dL, median (IQR) | 1.0 (0.9-1.1) | 1.0 (0.8-1.2) | 1.0 (0.9-1.1) | <0.001 |
| eGFRc stage, N (%) | <0.001 | |||
| eGFR, ≥60 | 4,080,191 (84%) | 87,880 (76%) | 3,992,311 (84%) | |
| Stage 3A, eGFR, 45-59 | 572,480 (12%) | 15,938 (14%) | 556,542 (12%) | |
| Stage 3B, eGFR, 30-44 | 177,056 (3.6%) | 8,129 (7.0%) | 168,927 (3.6%) | |
| Stage 4, eGFR, 15-29 | 34,849 (0.7%) | 3,797 (3.3%) | 31,052 (0.7%) | |
| Most recent proteinuria elevatedd, N (%) | 623,912 (13%) | 29,135 (25%) | 594,777 (13%) | <0.001 |
| Most recent proteinuria not elevatedd, N (%) | 3,797,304 (78%) | 77,568 (67%) | 3,719,736 (78%) | <0.001 |
| Missing, N (%) | 443,360 (9.1%) | 9,041 (7.8%) | 434,319 (9.1%) | <0.001 |
| Baseline proteinuria is “moderate”d, N (%) | 569,567 (12%) | 23,851 (21%) | 545,716 (12%) | <0.001 |
| Baseline proteinuria is “severe”d, N (%) | 54,345 (1.1%) | 5,284 (4.6%) | 49,061 (1.0%) | <0.001 |
| Baseline history of outpatient AKIe, N (%) | 322,564 (6.6%) | 20,484 (18%) | 302,080 (6.4%) | <0.001 |
| Baseline history of inpatient AKIf, N (%) | 119,253 (2.5%) | 9,184 (7.9%) | 110,069 (2.3%) | <0.001 |
| Number creatinine values at baseline, median (IQR) | 8 (4-17) | 12 (5-24) | 8 (4-17) | <0.001 |
| Diabetes mellitus, N (%) | 1,311,503 (27%) | 51,945 (45%) | 1,259,558 (27%) | <0.001 |
| Hypertension, N (%) | 3,024,529 (62%) | 90,739 (78%) | 2,933,790 (62%) | <0.001 |
| Cardiovascular diseaseg, N (%) | 1,259,851 (26%) | 45,748 (40%) | 1,214,103 (26%) | <0.001 |
| Coronary artery diseaseg, N (%) | 1,006,004 (21%) | 34,841 (30%) | 971,163 (21%) | <0.001 |
| Congestive heart failureg, N (%) | 221,907 (4.6%) | 14,361 (12%) | 207,546 (4.4%) | <0.001 |
| Strokeg, N (%) | 148,727 (3.1%) | 5,739 (5.0%) | 142,988 (3.0%) | <0.001 |
| Peripheral vascular diseaseg, N (%) | 271,887 (5.6%) | 12,792 (11%) | 259,095 (5.5%) | <0.001 |
| Liver disease, N (%) | 142,127 (2.9%) | 7,114 (6.1%) | 135,013 (2.8%) | <0.001 |
| Cancer, N (%) | 816,634 (17%) | 26,079 (23%) | 790,555 (17%) | <0.001 |
| Systolic blood pressure, mm Hg, median (IQR) | 129 (120-138) | 131 (120-142) | 129 (120-138) | <0.001 |
| Missing, N (%) | 18,296 (0.4%) | 517 (0.4%) | 17,779 (0.4%) | <0.001 |
| Diastolic blood pressure, mm Hg, median (IQR) | 77 (70-84) | 76 (68-84) | 77 (70-84) | <0.001 |
| Missing, N (%) | 21,091 (0.4%) | 593 (0.5%) | 20,498 (0.4%) | <0.001 |
| Sodium level, mmol/L, median (IQR) | 139 (138-141) | 139 (137-141) | 139 (138-141) | <0.001 |
| Missing, N (%) | 11,946 (0.2%) | 325 (0.3%) | 11,621 (0.2%) | 0.01 |
| Potassium level, mmol/L, median (IQR) | 4.2 (4.0-4.5) | 4.2 (3.9-4.5) | 4.2 (4.0-4.5) | <0.001 |
| Missing, N (%) | 33,930 (0.7%) | 816 (0.7%) | 33,114 (0.7%) | 0.76 |
| Calcium level, mg/dL, median (IQR) | 9.3 (9.0-9.6) | 9.3 (9.0-9.6) | 9.3 (9.0-9.6) | <0.001 |
| Missing, N (%) | 259,971 (5.3%) | 4,733 (4.1%) | 255,238 (5.4%) | <0.001 |
| Hemoglobin, g/dL, median (IQR) | 14.5 (13.5-15.4) | 13.8 (12.5-14.9) | 14.5 (13.5-15.4) | <0.001 |
| Missing, N (%) | 77,238 (1.6%) | 1,614 (1.4%) | 75,624 (1.6%) | <0.001 |
| Albumin level, g/dL, median (IQR) | 4.1 (3.8-4.3) | 4.0 (3.6-4.2) | 4.1 (3.8-4.3) | <0.001 |
| Missing, N (%) | 330,596 (6.8%) | 5,750 (5.0%) | 324,846 (6.8%) | <0.001 |
| Hemoglobin A1c in percentage, median (IQR) | 5.9 (5.5-6.5) | 6.1 (5.6-7.2) | 5.9 (5.5-6.5) | <0.001 |
| Missing, N (%) | 1,212,012 (25%) | 20,102 (17%) | 1,191,910 (25%) | <0.001 |
| Baseline history of hospitalization, N (%) | 1,069,398 (22%) | 44,850 (39%) | 1,024,548 (22%) | <0.001 |
Note: Conversion factors for units: creatinine in mg/dL to μmol/L, ×88.4; calcium in mg/dL to mmol/L, ×0.2495.
Abbreviations: AKI, acute kidney injury; eGFR, estimated glomerular filtration rate; IQR, interquartile range.
Outcome of AKI occurring and managed in the outpatient setting over an 18-month period.
Two sample t test or χ2 test, as applicable, applied to those with outpatient AKI versus those without.
eGFR, by the Modification of Diet in Renal Disease Study equation,23 in mL/min per 1.73 m2.
Proteinuria defined as the most recent of spot albuminuria, spot total proteinuria, or semiquantitative albuminuria by urinalysis, derived from Table 7 of the Kidney Disease Improving Global Outcomes 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease.27 “Severe” = spot albuminuria or total proteinuria ≥300 mg/g or albuminuria by urinalysis of “300” or equivalent. “Moderate” = spot albuminuria or total proteinuria ≥30 mg/g or albuminuria by urinalysis of “30” or equivalent. “Normal” or not elevated if otherwise measured.
Baseline history of AKI occurring and managed in the outpatient setting.
Baseline history of AKI managed in the inpatient setting regardless of setting of onset.
Cardiovascular disease defined as the composite of coronary artery disease, congestive heart failure, stroke, or peripheral vascular disease as nonmutually exclusive categories.