Results of regression models describing the demographic characteristics, the presence/absence of chronic conditions and drug prescription and associations with the frequency of serum creatinine testing in primary care
| Characteristic | Univariable IRR (95% CI) | Minimally adjusted IRR (95% CI) | Fully adjusted IRR (95% CI) |
| Gender | |||
| Female | 1.20 (1.20 to 1.21) | 1.18 (1.18 to 1.18) | 1.14 (1.14 to 1.14) |
| Age (years) | |||
| 40–49 | 2.09 (2.08 to 2.10) | 2.10 (2.09 to 2.11) | 1.92 (1.91 to 1.92) |
| 50–59 | 3.50 (3.49 to 3.51) | 3.53 (3.52 to 3.54) | 2.87 (2.86 to 2.88) |
| 60–69 | 5.38 (5.36 to 5.40) | 5.39 (5.37 to 5.41) | 3.94 (3.93 to 3.96) |
| 70–79 | 7.25 (7.22 to 7.27) | 7.23 (7.20 to 7.26) | 4.83 (4.81 to 4.85) |
| 80–89 | 7.57 (7.53 to 7.61) | 7.47 (7.43 to 7.51) | 4.86 (4.83 to 4.88) |
| ≥90 | 6.17 (6.10 to 6.25) | 5.94 (5.87 to 6.01) | 4.05 (4.00 to 4.10) |
| Ethnicity | |||
| Asian | 0.78 (0.77 to 0.79) | 1.25 (1.24 to 1.27) | 1.23 (1.22 to 1.24) |
| Black | 0.77 (0.76 to 0.78) | 1.19 (1.18 to 1.21) | 1.16 (1.14 to 1.17) |
| Mixed | 0.96 (0.96 to 0.97) | 1.00 (1.00 to 1.01) | 1.00 (1.00 to 1.00) |
| Other | 0.71 (0.69 to 0.72) | 1.05 (1.03 to 1.06) | 1.04 (1.02 to 1.05) |
| Not recorded | 0.83 (0.83 to 0.83) | 0.84 (0.84 to 0.84) | 0.84 (0.84 to 0.84) |
| Index of multiple deprivation | |||
| 2 | 1.07 (1.06 to 1.07) | 1.04 (1.04 to 1.05) | 1.03 (1.02 to 1.03) |
| 3 | 1.07 (1.06 to 1.07) | 1.07 (1.06 to 1.07) | 1.04 (1.04 to 1.04) |
| 4 | 1.03 (1.03 to 1.04) | 1.11 (1.11 to 1.12) | 1.08 (1.07 to 1.08) |
| 5 (most deprived) | 1.04 (1.03 to 1.04) | 1.14 (1.13 to 1.14) | 1.09 (1.08 to 1.09) |
| Not recorded | 1.05 (1.05 to 1.05) | 1.07 (1.07 to 1.08) | 1.03 (1.03 to 1.04) |
| Year of study entry | |||
| 2006 | 0.72 (0.71 to 0.72) | 0.96 (0.95 to 0.96) | 1.08 (1.08 to 1.09) |
| 2007 | 0.78 (0.77 to 0.78) | 0.96 (0.95 to 0.96) | 1.10 (1.09 to 1.10) |
| 2008 | 0.81 (0.80 to 0.81) | 0.99 (0.98 to 1.00) | 1.13 (1.13 to 1.14) |
| 2009 | 0.77 (0.76 to 0.78) | 1.00 (0.99 to 1.01) | 1.13 (1.12 to 1.14) |
| 2010 | 0.83 (0.82 to 0.83) | 1.04 (1.03 to 1.04) | 1.17 (1.17 to 1.18) |
| 2011 | 0.92 (0.92 to 0.93) | 1.11 (1.10 to 1.12) | 1.29 (1.28 to 1.30) |
| 2012 | 0.96 (0.95 to 0.97) | 1.18 (1.16 to 1.19) | 1.34 (1.33 to 1.35) |
| Region | |||
| East Midlands | 1.29 (1.28 to 1.30) | 1.18 (1.17 to 1.19) | 1.07 (1.07 to 1.08) |
| East of England | 1.18 (1.17 to 1.18) | 1.09 (1.09 to 1.10) | 1.04 (1.04 to 1.05) |
| North East | 1.44 (1.42 to 1.45) | 1.27 (1.26 to 1.28) | 1.20 (1.19 to 1.21) |
| North West | 1.30 (1.29 to 1.31) | 1.18 (1.18 to 1.19) | 1.10 (1.10 to 1.11) |
| South Central | 1.21 (1.20 to 1.22) | 1.14 (1.13 to 1.14) | 1.10 (1.09 to 1.10) |
| South East Coast | 1.23 (1.22 to 1.24) | 1.12 (1.11 to 1.12) | 1.10 (1.10 to 1.11) |
| South West | 1.43 (1.42 to 1.44) | 1.22 (1.22 to 1.23) | 1.17 (1.17 to 1.18) |
| West Midlands | 1.24 (1.24 to 1.25) | 1.14 (1.13 to 1.15) | 1.08 (1.07 to 1.08) |
| Yorkshire and The Humber | 1.24 (1.23 to 1.25) | 1.08 (1.07 to 1.09) | 0.97 (0.96 to 0.97) |
| Northern Ireland | 1.51 (1.50 to 1.53) | 1.55 (1.54 to 1.57) | 1.48 (1.47 to 1.49) |
| Scotland | 1.21 (1.20 to 1.22) | 1.22 (1.21 to 1.22) | 1.21 (1.20 to 1.22) |
| Wales | 1.33 (1.32 to 1.34) | 1.26 (1.26 to 1.27) | 1.22 (1.21 to 1.22) |
| Chronic kidney disease stage | |||
| 1 | 1.93 (1.76 to 2.11) | 2.18 (2.03 to 2.35) | 2.05 (1.92 to 2.19) |
| 2 | 2.30 (2.21 to 2.40) | 1.82 (1.76 to 1.88) | 1.93 (1.87 to 1.99) |
| 3 | 3.32 (3.25 to 3.40) | 1.67 (1.64 to 1.70) | 1.48 (1.46 to 1.51) |
| 4 | 4.98 (4.60 to 5.39) | 2.61 (2.45 to 2.77) | 2.17 (2.05 to 2.30) |
| 5 | 3.92 (3.05 to 5.03) | 2.37 (1.94 to 2.89) | 1.74 (1.45 to 2.09) |
| Comorbidities | |||
| Atrial fibrillation | 3.09 (3.04 to 3.13) | 1.00 (0.99 to 1.02) | |
| Cancer | 2.14 (2.12 to 2.17) | 1.15 (1.14 to 1.16) | |
| Diabetes | 3.48 (3.45 to 3.51) | 1.98 (1.97 to 1.99) | |
| Heart failure | 3.89 (3.83 to 3.95) | 1.07 (1.05 to 1.08) | |
| Hypertension | 2.37 (2.37 to 2.38) | 1.28 (1.28 to 1.29) | |
| Ischaemic heart disease | 2.76 (2.73 to 2.78) | 1.23 (1.23 to 1.24) | |
| Peripheral vascular disease | 2.55 (2.52 to 2.58) | 1.20 (1.19 to 1.21) | |
| Stroke/transient ischaemic attack | 2.85 (2.81 to 2.88) | 1.14 (1.13 to 1.15) | |
| Thyroid disease | 2.09 (2.07 to 2.11) | 1.31 (1.30 to 1.32) | |
| Pharmacotherapies | |||
| ACE inhibitors | 3.20 (3.18 to 3.21) | 1.41 (1.41 to 1.42) | |
| ARBs | 2.98 (2.96 to 3.00) | 1.25 (1.24 to 1.26) | |
| Amiodarone/dronedarone | 3.49 (3.41 to 3.56) | 1.15 (1.13 to 1.17) | |
| Digoxin | 3.39 (3.34 to 3.44) | 1.17 (1.16 to 1.19) | |
| Diuretics | 3.27 (3.25 to 3.28) | 1.46 (1.46 to 1.47) | |
| Ethambutol | 1.37 (1.09 to 1.73) | 1.16 (0.97 to 1.40) | |
| Gold | 11.11 (9.59 to 12.88) | 5.48 (4.95 to 6.07) | |
| Immunosuppressants (not including methotrexate) | 5.06 (4.97 to 5.15) | 3.44 (3.40 to 3.49) | |
| Lithium | 4.14 (4.00 to 4.28) | 4.42 (4.32 to 4.52) | |
| Mesalazine | 2.44 (2.37 to 2.50) | 2.23 (2.19 to 2.28) | |
| Methotrexate | 9.41 (9.19 to 9.64) | 6.17 (6.07 to 6.28) | |
| NSAIDs | 1.55 (1.55 to 1.56) | 1.25 (1.25 to 1.25) | |
| Oral anticoagulants | 2.93 (2.89 to 2.96) | 1.17 (1.16 to 1.18) | |
IRR, incidence rate ratio; NSAIDs, non-steroidal anti-inflammatory drugs.