Determining the Association Between Continuity of Primary Care and Acute Care Use in Chronic Kidney Disease: A Retrospective Cohort Study

Christy Chong; David Campbell; Meghan Elliott; Fariba Aghajafari; Paul Ronksley

doi:10.1370/afm.2813

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Figure 1.
Criteria to determine final study cohort.
CKD = chronic kidney disease; eGFR = estimated glomerular filtration rate.

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Table 1.

Patient Demographic and Clinical Characteristics by Continuity of Primary Care

Patient Characteristic	Level of Relational Continuity of Primary Care
Patient Characteristic	Poor	Moderate	High	Overall
Patients, No. (%)	16,143 (18.7)	25,948 (30.0)	44,384 (51.3)	86,475 (100.0)
CKD stage, No. (%)^{^a}
3a	9,153 (56.7)	15,489 (59.7)	27,274 (61.5)	51,916 (60.0)
3b	5,145 (31.9)	7,960 (30.7)	13,313 (30.0)	26,418 (30.5)
4	1,845 (11.4)	2,499 (9.6)	3,797 (8.6)	8,141 (9.4)
Age, y, mean (SD)	76.1 (12.6)	75.7 (11.4)	76.2 (10.5)	76.0 (11.2)
Age category, y, No. (%)
18-44	360 (2.2)	357 (1.4)	364 (0.8)	1,081 (1.3)
45-64	2,469 (15.3)	3,930 (15.1)	5,880 (13.2)	12,279 (14.2)
65-74	3,611 (22.4)	6,697 (25.8)	11,926 (26.9)	22,234 (25.7)
75-84	5,571 (34.5)	9,492 (36.6)	17,326 (39.0)	32,389 (37.5)
≥85	4,132 (25.6)	5,472 (21.1)	8,888 (20.0)	18,492 (21.4)
Female, No. (%)	9,571 (59.3)	14,902 (57.4)	24,483 (55.2)	48,956 (56.6)
Location of residence,	No. (%)
Urban	13,221 (82.0)	21,978 (84.7)	40,339 (90.9)	75,538 (87.4)
Rural	2,909 (18.0)	3,932 (15.2)	3,988 (9.0)	10,829 (12.5)
Albuminuria, No. (%)
Normal/mild (A1)	7,601 (47.1)	13,458 (51.9)	23,991 (54.1)	45,050 (52.1)
Moderate (A2)	2,021 (12.5)	3,221 (12.4)	5,660 (12.8)	10,902 (12.6)
Severe (A3)	1,440 (8.9)	2,007 (7.7)	2,979 (6.7)	6,426 (7.4)
Unmeasured	5,081 (31.5)	7,262 (28.0)	11,754 (26.5)	24,097 (27.9)
Median household income quintile, No. (%)
1 (lowest)	4,627 (28.7)	6,944 (26.8)	11,130 (25.1)	22,701 (26.3)
2	3,673 (22.8)	5,893 (22.7)	10,036 (22.6)	19,602 (22.7)
3	2,958 (18.3)	5,012 (19.3)	8,735 (19.7)	16,705 (19.3)
4	2,246 (13.9)	3,687 (14.2)	6,576 (14.8)	12,509 (14.5)
5 (highest)	2,062 (12.8)	3,686 (14.2)	6,986 (15.7)	12,734 (14.7)
6 (unknown)	577 (3.6)	726 (2.8)	921 (2.1)	2,224 (2.6)
Comorbidities, No. (%)
Asthma	1,106 (6.9)	1,385 (5.3)	1,699 (3.8)	4,190 (4.8)
Atrial fibrillation	3,472 (21.5)	4,741 (18.3)	7,241 (16.3)	15,455 (17.9)
Cancer	1,723 (10.7)	2,573 (9.9)	3,785 (8.5)	8,081 (9.3)
Congestive heart failure	4,635 (28.7)	5,785 (22.3)	8,068 (18.2)	18,488 (21.4)
Chronic obstructive pulmonary disease	5,379 (33.3)	7,239 (27.9)	10,000 (22.5)	22,618 (26.2)
Cirrhosis	168 (1.0)	142 (0.5)	186 (0.4)	496 (0.6)
Diabetes	5,871 (36.4)	8,848 (34.1)	15,497 (34.9)	30,216 (34.9)
Hypertension	14,008 (86.8)	22,293 (85.9)	38,475 (86.7)	74,776 (86.5)
Peripheral vascular disease	1,084 (6.7)	1,413 (5.4)	2,052 (4.6)	4,549 (5.3)
Comorbidities, mean (SD)	3.9 (2.3)	3.3 (2.0)	3.0 (1.8)	3.2 (2.0)
≥1 Visit to a specialist in a 2-year period before index date, No. (%)
Nephrology	2,350 (14.6)	3,228 (12.4)	4,788 (10.8)	10,366 (12.0)
Endocrinology	187 (1.2)	228 (0.9)	310 (0.7)	725 (0.8)
Oncology	49 (0.3)	39 (0.2)	34 (0.1)	122 (0.1)
Psychiatry	1,756 (10.9)	1,591 (6.1)	1,591 (3.6)	4,938 (5.7)
Cardiology	4,332 (26.8)	6,344 (24.4)	10,001 (22.5)	20,677 (23.9)
Respiratory	1,600 (9.9)	2,198 (8.5)	2,797 (6.3)	6,595 (7.6)
Internal medicine	9,095 (56.3)	13,088 (50.4)	20,713 (46.7)	42,896 (49.6)

CKD = chronic kidney disease; eGFR = estimated glomerular filtration rate.
↵a CKD stages were defined as stage 3a (eGFR 45-59 mL/min/1.73 m²), stage 3b (eGFR 30-44 mL/min/1.73 m²), and stage 4 (eGFR 15-29 mL/min/1.73 m²).

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Table 2.

All-Cause and Ambulatory Care-Sensitive Condition–Related Hospitalizations and Emergency Department Visit Characteristics by Continuity of Primary Care

	Variable	Level of Relational Continuity of Primary Care			Overall (n = 86,475)
	Variable	Poor (n = 16,143)	Moderate (n = 25,948)	High (n = 44,384)	Overall (n = 86,475)
All-cause hospitalizations	Patients, No.	7,938	11,020	15,852	34,810
	Hospitalizations, No. (%)	19,835 (25.4)	25,551 (32.8)	32,602 (41.8)	77,988 (100.0)
	Hospitalizations, median (IQR)	0 (0-2)	0 (0-1)	0 (0-1)	0 (0-1)
	Person-time, y (%)	32,328.8 (17.9)	53,698.6 (29.7)	94,520.5 (52.4)	180,547.9 (100.0)
	Length of hospital stay, d, mean (SD)	13.7 (21.1)	12.8 (19.2)	12.7 (20.0)	12.9 (20.0)
	Length of hospital stay, d, median (IQR)	0 (0-7)	0 (0-5)	0 (0-4)	0 (0-5)
	Cumulative length of hospital stay, d, median (IQR)	15 (6-42)	13 (5-39)	11 (4-33)	13 (5-37)
	Unadjusted hospitalization rate/1,000 person-years (95% CI)	613.5	475.8	344.9	432.0
	Unadjusted hospitalization rate/1,000 person-years (95% CI)	(605.6-622.7)	(470.2-481.9)	(341.9-349.4)	(429.5-435.6)
	Patients, No.	1,095	1,369	1,842	4,306
ACSC-related hospitalizations	ACSC hospitalizations, No. (%)	1,714 (26.4)	2,045 (31.5)	2,730 (42.1)	6,489 (100.0)
	ACSC hospitalizations, median (IQR)	0 (0)	0 (0)	0 (0)	0 (0)
	Person-time, y (%)	32,328.8 (17.9)	53,698.6 (29.7)	94,520.5 (52.4)	180,547.9 (100.0)
	Length of hospital stay, d, mean (SD)	1.6 (6.7)	1.4 (5.7)	1.4 (6.0)	1.4 (6.1)
	Length of hospital stay, d, median (IQR)	0 (0)	0 (0)	0 (0)	0 (0)
	Cumulative length of hospital stay, d, median (IQR)	0 (0-7)	0 (0-5)	0 (0-4)	0 (0-5)
	Unadjusted ACSC hospitalization rate/1,000 person-years (95% CI)	53.1	38.1	28.9	36.0
		(50.6-55.6)	(36.5-39.8)	(27.9-30.1)	(35.1-36.9)
All-cause ED visits	Patients, No.	11,234	16,237	23,681	51,152
	ED visits, No. (%)	56,809 (27.8)	70,147 (34.3)	77,659 (38.0)	204,615 (100.0)
	ED visits, median (IQR)	2 (0-4)	1 (0-3)	1 (0-2)	1 (0-3)
	Person-time, y (%)	32,328.8 (17.9)	53,698.6 (29.7)	94,520.5 (52.4)	180,547.9 (100.0)
	Unadjusted ED visit rate/1,000 person-years (95% CI)	1,757.2	1,306.3	823.4	1,133.3
	Unadjusted ED visit rate/1,000 person-years (95% CI)	(1,744.3-1,773.3)	(1,297.2-1,316.5)	(817.6-829.2)	(1,129.9-1,139.8)
ACSC-related ED visits	Patients, No.	1,414	1,731	2,272	5,417
	ACSC ED visits, No. (%)	2,294 (27.1)	2,726 (32.2)	3,441 (40.7)	8,461 (100.0)
	ACSC ED visits, median (IQR)	0 (0)	0 (0)	0 (0)	0 (0)
	Person-time, y (%)	32,328.8 (17.9)	53,698.6 (29.7)	94,520.5 (52.4)	180,547.9 (100.0)
	Unadjusted ACSC ED visits rate/1,000 person-years (95% CI)	71.0	50.8	36.5	46.9
	Unadjusted ACSC ED visits rate/1,000 person-years (95% CI)	(68.2-74.0)	(48.9-62.7)	(35.3-37.7)	(45.9-47.9)

ACSC = ambulatory care-sensitive condition; ED = emergency department; IQR = interquartile range.

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Table 3.

Unadjusted and Adjusted Incident Rate Ratios for Health Care Utilization (All-Cause and Ambulatory Care-Sensitive Condition-Related Hospitalizations and Emergency Department Visits) and Process of Care Outcomes by Continuity of Primary Care

		Variable	Level of Relational Continuity of Pimary Care			Overall (n = 86,475)
		Variable	Poor (n = 16,143)	Moderate (n = 25,948)	High (n = 44,384)	Overall (n = 86,475)
Health care utilization outcomes	All-cause hospitalizations	Patients, No.	7,938	11,020	15,852	34,810
		All-cause hospitalizations, No.	19,835	25,551	32,602	77,988
		Unadjusted incident rate ratio of all-cause hospitalizations (95% CI)	1.85 (1.79-1.91)	1.41 (1.37-1.45)	(reference)
		Adjusted incident rate ratio of all-cause hospitalizations (95% CI)^{^a}	1.52 (1.47-1.57)	1.28 (1.25-1.32)	(reference)
	ACSC-related hospitalizations	Patients, No.	1,095	1,369	1,842	4,306
		ACSC-related hospitalizations, No.	1,714	2,045	2,730	6,489
		Unadjusted incident rate ratio of ACSC-related hospitalizations (95% CI)	1.96 (1.77-2.16)	1.35 (1.24-1.48)	(reference)
		Adjusted incident rate ratio of ACSC-related hospitalizations (95% CI)^{^b}	1.58 (1.44-1.74)	1.23 (1.13-1.34)	(reference)
	All-cause ED visits	Patients, No.	11,234	16,237	23,681	51,152
		All-cause ED visits, No.	56,809	70,147	77,659	204,615
		Unadjusted incident rate ratio of all-cause ED visits (95% CI)	2.18 (2.12-2.24)	1.6 (1.56-1.64)	(reference)
		Adjusted incident rate ratio of all-cause ED visits (95% CI)^{^a}	1.78 (1.73-1.83)	1.42 (1.39-1.46)	(reference)
	ACSC-related ED visits	Patients, No.	1,414	1,731	2,272	5,417
		ACSC-related ED visits, No.	2,294	2,726	3,441	8,461
		Unadjusted incident rate ratio of ACSC-related ED visits (95% CI)	2.1 (1.92-2.29)	1.44 (1.33-1.55)	(reference)
		Adjusted incident rate ratio of ACSC-related ED visits (95% CI)^{^b}	1.68 (1.54-1.82)	1.28 (1.19-1.38)	(reference)
	RAAS inhibitor	Patients, No.	9,387	14,500	24,761	48,648
Process of care outcomes		Unadjusted odds ratio (95% CI)	1.09 (1.05-1.14)	1.0 (0.97-1.03)	(reference)
		Adjusted odds ratio (95% CI)	1.03 (0.98-1.07)	0.99 (0.96-1.02)	(reference)
		Patients, No.	7,318	12,147	21,831	41,296
	Statin	Unadjusted odds ratio (95% CI)	0.75 (0.69-0.8)	0.86 (0.81-0.92)	(reference)
		Adjusted odds ratio (95% CI)	0.8 (0.74-0.86)	0.89 (0.84-0.95)	(reference)

ACSC = ambulatory care-sensitive condition; ED = emergency department; IQR = interquartile range; RAAS = renin-angiotensin-aldosterone system.
↵a Adjusted by age, sex, household location, median household income quintile, cirrhosis, chronic heart failure, peripheral vascular disease, atrial fibrillation, asthma, chronic obstructive pulmonary disease, cancer, diabetes, hypertension, and albuminuria severity.
↵b Adjusted by age, sex, household location, median household income quintile, cirrhosis, peripheral vascular disease, atrial fibrillation, asthma, chronic obstructive pulmonary disease, cancer, diabetes, and albuminuria severity.