How well can electronic health records from primary care identify Alzheimer’s disease cases?

Figures & data

Table 1 Algorithms to identify Alzheimer's disease (AD) cases in electronic health records from primary care, using codes from the international statistical classification of diseases and related health problems, version 10 (ICD-10) and from the Anatomical Therapeutic Chemical (ATC)

Algorithm	Definition of AD case
A1	Diagnosed patients: have an ICD10 code for AD (F00 or G30).
A2	Diagnosed or treated patients: have a code for AD (ICD10: F00 or G30) or for prescription or billing of anti-dementia drugs (ATC: N06DA, N06DX01).
A3	Diagnosed or treated patients without previous conditions: have a code for AD (ICD10: F00 or G30) or for prescription or billing of anti-dementia drugs (ATC: N06DA, N06DX01). Treated patients were included if they had no code of dementia diagnosis or had a code of unspecified dementia (F03), and were excluded if they had a code for: a specific subtype of dementia such as Lewy bodies dementia, vascular or frontotemporal dementia (ICD10: F01, F02); Parkinson (ICD10: G20-G22); anti-Parkinson drugs (ATC: N04); or cerebrovascular disease (ICD10:I60- I69, G45, G46) within two years prior to AD diagnosis.

Figure 1 Register of dementias of Girona (ReDeGi) and SIDIAP linkage flow diagram. Data confidentiality measures were applied during information transfer (encoded data in grey arrows; password in dotted grey lines).Abbreviation: SIDIAP, Information System for Research in Primary Care.

Figure 2 Flow of Alzheimer's disease (AD) diagnoses evaluated by general practitioners (GPs) responding to an online survey.

Table 2 Baseline demographic and clinical characteristics of patients according to the validation method: survey of general practitioners (GPs) to evaluate recorded AD diagnoses or linkage between datasets from primary (SIDIAP) and secondary care (ReDeGi)

	Survey		Dataset
	Evaluated patients (n=137)	Not-evaluated patients (n=51)	All selected patients (n=4,966)
Age, $\bar{\mathrm{X}}$ (sd)	80.9 (7.7)	83.5 (6.9)	80.2 (6.9)
Women, n (%)	92 (67%)	36 (70%)	3151 (63%)
Deprivation index, n (%)
Quintile 1: less deprived	12 (9%)	1 (2%)	629 (22.64)
Quintile 2	32 (23%)	14 (27%)	472 (16.99)
Quintile 3	21 (15%)	8 (16%)	545 (19.62)
Quintile 4	34 (25%)	13 (26%)	653 (23.51)
Quintile 5: more deprived	38 (28%)	15 (29%)	479 (17.24)
Antidementia drugs, n (%)	92 (67%)	32 (63%)	3275 (66%)
Severity of dementia, n (%)
Mild	-	-	2955 (60%)
Moderate	-	-	1532 (31%)
Severe	-	-	437 (9%)

Table 3 Positive predictive value (PPV) of Alzheimer's disease (AD) diagnoses recorded in SIDIAP using information provided by the survey of general practitioners as reference. Sensitivity analysis included all AD patients of participating general practitioners (whether their diagnoses were evaluated or not)

Population	n	Main analysis			n	Sensitivity analysis
		TP	FP	PPV (95% CI)		TP	FP	PPV (95% CI)
Women	92	84	8	91.3 (85.5–97.1)	128	106	22	82.8 (77.0–87.8)
Men	45	39	6	86.7 (76.7–96.6)	60	49	11	81.6 (71.9–91.4)
<80 years	84	74	10	88.1 (79.9–94.2)	105	89	16	84.8 (77.9–91.6)
≥80 years	54	49	4	92.4 (87.8–100.5)	83	66	17	79.5 (70.8–88.2)
Total	137	123	14	89.8 (84.7–94.9)	188	155	33	82.4 (77.0–87.8)

Abbreviations: TP, true positive; FP, false positive; SIDIAP, Information System for Research in Primary Care.

Table 4 Positive predictive value (PPV) and sensitivity of Alzheimer's disease (AD) diagnoses in SIDIAP using three algorithms to define AD cases and linkage with the register of dementias of Girona as reference

Algorithm	Group	Subgroup	TP	FP	FN	PPV (95% CI)	Sensitivity (95% CI)
A1. Diagnosed patients
	Sex	Women	1,365	398	528	77.4 (75.4–79.3)	72.1 (70.0–74.1)
		Men	582	258	253	69.3 (66.1–72.3)	69.3 (66.1–72.3)
	Age	<80 years	843	285	275	74.9 (72.3–77.4)	75.4 (72.8–77.8)
		≥80 years	1,104	371	506	74.8 (72.5–77.0)	68.6 (66.3–70.8)
	Severity	Mild	1346	386	434	77.7 (75.7–79.6)	75.6 (73.6–77.6)
		Moderate	472	220	263	68.2 (64.6–71.6)	64.2 (60.7–67.7)
		Severe	123	43	83	74.1 (66.9–80.2)	59.7 (52.9–66.2)
	Total population		1,947	656	781	74.8 (73.1–76.4)	71.4 (69.6–73.0)
A2. Diagnosed or treated patients
	Sex	Women	1,623	715	270	69.4 (67.5–71.3)	85.7 (84.1–87.2)
		Men	711	484	124	59.5 (56.7–62.2)	85.1 (82.6–87.4)
	Age	<80 years	992	531	126	65.1 (62.7–67.5)	88.7 (86.7–90.4)
		≥80 years	1,342	668	268	66.8 (64.7–68.8)	83.4 (81.4–85.1)
	Severity	Mild	1585	703	195	69.3 (67.4–71.1)	89.0 (87.5–90.4)
		Moderate	590	391	145	60.1 (57.0–63.2)	80.3 (77.2–83.0)
		Severe	152	87	54	63.6 (57.3–69.4)	73.8 (67.4–79.3)
	Total population		2,334	1,199	394	66.1 (64.5–67.6)	85.6 (84.2–86.8)
A3. Diagnosed or treated patients without previous conditions
	Sex	Women	1,599	558	294	74.6 (72.7–76.4)	83.9 (82.2–85.5)
		Men	687	346	148	67.5 (64.5–70.3)	81.8 (79.0–84.3)
	Age	<80 years	973	378	145	72.7 (70.3–75.0)	86.7 (84.6–88.6)
		≥80 years	1,313	527	297	72.1 (69.9–74.1)	80.9 (78.9–82.7)
	Severity	Mild	1552	519	228	74.9 (73.0–76.7)	87.2 (85.6–88.7)
		Moderate	569	280	166	67.0 (63.8–70.1)	77.4 (74.3–80.3)
		Severe	144	59	62	70.9 (64.3–76.7)	69.9 (63.3–75.8)
	Total population		2,286	905	442	72.3 (70.7–73.9)	83.3 (81.8–84.6)

Abbreviations: TP, true positive; FP, false positive; FN, false negative; SIDIAP, Information System for Research in Primary Care.

Figure S1 Summary of survey for the validation of dementia diagnosis.Abbreviations: DSM-IV, Diagnostic and Statistical Manual of Mental Disorders, 4th edition; ICD-10, International Statistical Classification of Diseases and Related Health Problems, 10th edition.

Table S1 Description of the quota of patients from the 29 general practitioners who answered the survey

Sociodemographic characteristics	Quota of patients (n=29)
Percentage of men, $\bar{\mathrm{X}}$ (sd)	49.5 (3.4)
Age, $\bar{\mathrm{X}}$ (sd)	47.5 (2.0)
Percentage of people aged ≥65 years, $\bar{\mathrm{X}}$ (sd)	21.4 (4.9)
Number of patients, $\bar{\mathrm{X}}$ (sd)	1426 (331)
Rural areas, n (%)	5 (17.1)
Socioeconomic status in urban areas, n (%)
Status 1: less deprived	2 (8.3)
Status 2	2 (8.3)
Status 3	6 (25)
Status 4: more deprived	14 (58.3)