Detecting chronic kidney disease in population-based administrative databases using an algorithm of hospital encounter and physician claim codes

Table 1 Baseline characteristics

	N = 123499
Demographics
Age, years, median (IQR)	75 (70–81)
Women, n (%)	67207 (54.4)
Income quintile, *n (%)*
One (lowest)	24803 (20.1)
Two	24607 (19.9)
Three (middle)	25016 (20.3)
Four	23112 (18.7)
Five (highest)	24837 (20.1)
Rural Location, *n (%)*	25707 (20.8)
Comorbidities, *n (%)*
Coronary artery disease^¶	49027 (39.7)
Diabetes mellitus^£	28759 (23.3)
Heart failure	20259 (16.4)
Peripheral vascular disease	2730 (2.2)
Stroke/Transient ischemic attack	4812 (3.9)
Medication use in prior 6 months, *n (%)*
Angiotensin-converting enzyme inhibitors	49635 (40.2)
Angiotensin-receptor blockers	28438 (23.0)
Beta blockers	47051 (38.1)
Calcium channel blockers	40600 (32.9)
Loop diuretics	22860 (18.5)
NSAIDs(excluding aspirin)	26478 (21.4)
Warfarin	14967 (12.1)
Potassium sparing diuretics	9948 (8.1)
Statins	65168 (52.8)
Thiazide diuretics	27448 (22.2)
Baseline Laboratory Measurements*
Serum creatinine μmol/L, median (IQR)	84 (70–102)
eGFR category ^ŦmL/min per 1.73m², n (%)
≥60mL	78584 (63.6)
45-59	25904 (21.0)
30-44	13749 (11.1)
15-29	4624 (3.7)
<15	638 (0.5)
Serum sodium mmol/L, median, (IQR)	140 (138–142)
Serum potassium mmol/L, median (IQR)	4.2 (3.9-4.6)
Proteinuria (dipstick value) g/L
Category, n (%)
Negative	23792 (19.3)
0.3	1509 (1.2)
1.0	962 (0.8)
≥3.0	220 (0.2)

Abbreviations: IQR, interquartile range; NSAIDs, non-steroidal anti-inflammatory drugs; eGFR, estimated glomerular filtration rate.
^¶ Coronary artery disease includes receipt of coronary artery bypass graft surgery, percutaneous coronary intervention and diagnoses of angina.
^£ Assessed by diabetic medication use in previous 6 months.
* All patients had a serum creatinine measurement. A total of 109,743 (88.9%), and 111,304 (90.1%) patients had a serum sodium and potassium measurement in the year prior to cohort entry, respectively while 26,483(21.4%) patients had a urine dipstick protein value. The most recent values prior to the prescription date were used.
^ŦeGFR was calculated using the CKD-Epi equation.
CKD-Epi equation:141 x min([serum creatinine in umol/L /88 · 4 ]/κ, 1)^α x max([serum creatinine in umol/L / 88 · 4]/κ, 1)^-1·209 x 0 · 993^Age x 1 · 018 [if female] x 1 · 159 [if African American] κ = 0 · 7 for females and 0 · 9 for males, α = −0 · 329 for females and −0 · 411 for males, min = the minimum of Scr/κ or 1, max = the maximum of Scr/κ or 1.Racial information was not available in our data sources and all patients were assumed not to be of non African-Canadian race. This was a reasonable assumption; as of 2006, African-Canadians represented <7% of the Ontario population. Source: http://http://www12.statcan.ca/census-recensement/2006/dp-pd/hlt/97-562/index.cfm?Lang=E .

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