Construction and validation of a morbidity index based on the International Classification of Primary Care

Figures & data

Table 1. Application of ICPC-2 diagnostic codes to 38 morbidities collected from a database of 1 751 841 people registered with 314 medical practices in Scotland [15].

Odds ratio (OR) for death in 2018, based on the same ICPC-2 diagnoses recorded in Norway during 2015–2017. All 38 morbidities were included in a single multivariable logistic regression analysis, adjusted for gender and age. The 18 morbidities marked in bold were included in the final ICPC morbidity index. Data material: Norwegian born (N = 4 509 382).

Morbidities 2015–2017	ICPC-2 codes	Number of patients	Death 2018
			Regression coefficient (B)	OR	95 % CI
Cancer	A79, B72, B73, B74, D74, D75, D76, D77, L71, N74, R84, R85, T71, U75. U76, U77, W72, X75, X76, X77, Y77, Y78	119 824	1.15	3.16	3.08 − 3.25
Viral hepatitis	D72	6 515	0.80	2.23	1.81 − 2.75
Dyspepsia	D84, D85, D86, D87	153 547	0.01	1.01	0.97 − 1.06
Diverticular disease of intestine	D92	24 825	−0.23	0.80	0.72 − 0.88
Irritable bowel disorder	D93	28 492	−0.47	0.63	0.51 − 0.76
Inflammatory bowel disease	D94	32 685	0.10	1.11	0.98 − 1.25
Chronic liver disease	D97	18 412	0.63	1.88	1.70 − 2.07
Glaucoma	F93	18 908	0.01	1.01	0.94 − 1.08
Blindness & low vision	F94	7 778	0.18	1.19	1.05 − 1.35
Hearing loss	H83, H84, H85, H86	48 094	−0.21	0.81	0.77 − 0.86
Coronary heart disease	K74, K75, K76	116 144	−0.05	0.95	0.92 − 0.98
Heart failure	K77	39 279	0.86	2.37	2.29 − 2.46
Atrial fibrillation	K78	96 002	0.16	1.17	1.13 − 1.21
Hypertension	K86, K87	527 280	−0.32	0.73	0.71 − 0.74
Stroke & transient ischaemic attack	K89, K90	64 506	0.34	1.41	1.36 − 1.47
Peripheral vascular disease	K92	29 022	0.26	1.29	1.21 − 1.37
Painful condition	L18, L83, L84, L85, L86, L89, L90, L91, L92, N90, N94, N95	878 845	−0.37	0.69	0.67 − 0.71
Rheumatoid arthritis, other inflammatory polyarthropathies & systematic connective tissue disorders	L88	61 630	0.16	1.18	1.11 − 1.25
Multiple sclerosis	N86	11 901	0.79	2.21	1.88 − 2.59
Parkinson’s disease	N87	11 356	0.87	2.38	2.22 − 2.56
Epilepsy	N88	32 879	0.75	2.11	1.94 − 2.29
Migraine	N89	120 858	−0.23	0.79	0.69 − 0.91
Alcohol problems	P15	27 488	1.05	2.87	2.66 − 3.09
Other psychoactive substance misuse	P18, P19	34 167	1.36	3.88	3.50 − 4.30
Learning disability	P24, P85	26 392	1.11	3.04	2.62 − 3.52
Dementia	P70	31 374	1.09	2.96	2.86 − 3.06
Schizophrenia (and related nonorganic psychosis) or bipolar disorder	P72, P73, P98	46 734	0.75	2.12	1.96 − 2.29
Anxiety & other neurotic, stress related & somatoform disorders	P74, P75, P82	131 149	0.22	1.24	1.17 − 1.32
Depression	P76	271 031	0.23	1.26	1.21 − 1.32
Anorexia or bulimia	P86	4 394	0.91	2.48	1.43 − 4.29
Sinusitis	R75	201 324	−0.42	0.66	0.60 − 0.71
Chronic obstructive pulmonary disease	R95	91 012	0.77	2.17	2.10 − 2.24
Asthma	R96	248 978	−0.10	0.91	0.86 − 0.95
Psoriasis or eczema	S86, S87, S88, S91	335 956	−0.09	0.91	0.87 − 0.95
Thyroid disorders	T85, T86	155 695	−0.13	0.88	0.84 − 0.92
Diabetes	T89, T90	186 227	0.27	1.30	1.26 − 1.34
Chronic kidney disease	U88	3 167	0.72	2.05	1.64 − 2.55
Prostate disorders	Y85	47 836	−0.28	0.76	0.71 − 0.80

Table 2. Predictability of alternative ICPC morbidity indices (different number of morbidities included) for death in 2018 among Norwegian born people living in Norway (N = 4 509 382).

The table also includes a similar analysis of the Charlson index in the same population.

	N	OR	95 % CI
ICPC morbidity index with 16 morbidities
1	405 528	3.23	3.15 − 3.30
2	64 734	5.93	5.73 − 6.13
3+	10 948	9.96	936 − 10.59
Sum	481 210	AUC: 0.76 (0.76 − 0.76)
ICPC morbidity index with 17 morbidities
1	505 092	2.73	2.66 − 2.80
2	95 176	4.98	4.83 − 5.14
3+	19 015	8.58	8.17 − 9.02
Sum	619 283	AUC: 0.77 (0.77 − 0.78)
ICPC morbidity index with 18 morbidities
1	512 531	2.68	2.61 − 2.74
2	101 196	4.81	4.66 − 4.96
3+	21 914	8.12	7.75 − 8.50
Sum	635 641	AUC: 0.78 (0.77 − 0.78)
ICPC morbidity index with 19 morbidities
1	659 346	2.49	2.43 − 2.55
2	141 596	4.52	4.39 − 4.66
3+	35 139	7.42	7.12 − 7.74
Sum	836 081	AUC: 0.77 (0.77 − 0.77)
ICPC morbidity index with 20 morbidities
1	681 603	2.43	2.37 − 2.49
2	172 544	4.28	4.15 − 4.41
3+	49 087	7.14	6.86 − 7.43
Sum	903 234	AUC: 0.76 (0.76 − 0.77)
Charlson index
1	452 152	1.85	1.80 − 1.90
2	104 851	4.19	4.07 − 4.32
3+	45 774	7.77	7.52 − 8.02
Sum	602 777	AUC: 0.77 (0.76 − 0.77)

Odds ratio (OR) adjusted for gender and age. Multivariable logistic regression analyses with zero morbidities as reference category. AUC: Area under curve.

Figure 1. Receiver operating characteristic (ROC) curves for the ICPC morbidity index, the Charlson index and age as predictors of death in 2018 among Norwegian born people living in Norway (N = 4 509 382).

Table 3. Predictability of the ICPC morbidity index and the Charlson index for death among foreign-born people living in Norway (N = 959 496).

	N	OR	95 % CI
ICPC morbidity index
1	69 216	3.37	3.04 − 3.72
2	7 818	7.68	6.59 − 8.95
3+	1 928	15.11	12.07 − 18.93
Sum	78 962	AUC: 0.76 (0.75 − 0.78)
Charlson index
1	54 408	2.57	2.28 − 2.89
2	9 673	6.93	6.08 − 7.89
3+	3 537	13.07	11.35 − 15.04
Sum	67 618	AUC: 0.77 (0.75 − 0.78)

Odds ratio (OR) adjusted for gender and age. Multivariable logistic regression analyses with zero morbidities as reference category. AUC: Area under curve.

Table 4. The ICPC morbidity index comprises 18 morbidities with the following ICPC-2 diagnostic codes.

Morbidities	ICPC-2 codes
Cancer	A79, B72, B73, B74, D74, D75, D76, D77, L71, N74, R84, R85, T71, U75. U76, U77, W72, X75, X76, X77, Y77, Y78
Viral hepatitis	D72
Chronic liver disease	D97
Heart failure	K77
Stroke & transient ischaemic attack	K89, K90
Peripheral vascular disease	K92
Multiple sclerosis	N86
Parkinson’s disease	N87
Epilepsy	N88
Alcohol problems	P15
Other psychoactive substance misuse	P18, P19
Learning disability	P24, P85
Dementia	P70
Schizophrenia (and related nonorganic psychosis) or bipolar disorder	P72, P73, P98
Anorexia or bulimia	P86
Chronic obstructive pulmonary disease	R95
Diabetes	T89, T90
Chronic kidney disease	U88

Barnett K, Mercer SW, Norbury M, et al. Epidemiology of multimorbidity and implications for health care, research, and medical education: a cross-sectional study. Lancet. 2012;380(9836):37–43.

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