The internal validation of weight and weight change coding using weight measurement data within the UK primary care Electronic Health Record

Figures & data

Figure 1 Flowchart of candidate code categorization.

Table 1 The face validity of the 30 most commonly used abnormal weight codes

Abnormal weight code	Instances of code	Male	Same day weight measurements
	N	n (%)	n (%)	Mean
				kg (95% CI)	BMI (95% CI)
O/E – underweight	2,601	755 (29)	1,518 (58)	48.2 (47.8–48.6)	17.4 (17.3–17.4)
BMI <20	2,294	614 (27)	1,180 (51)	50.7 (50.3–51.2)	18.3 (18.2–18.4)
BMI low kg/m^2	4,751	1,267 (27)	3,799 (80)	53 (52.6–53.3)	19.2 (19.1–19.3)
BMI normal kg/m^2	62,233	22,035 (35)	47,745 (77)	63.7 (63.6–63.8)	22.8 (22.8–22.8)
BMI 20–24 – normal	6,579	2,315 (35)	5,565 (85)	64.1 (63.9–64.3)	22.9 (22.8–22.9)
BMI 25–29 – overweight	24,778	12,002 (48)	15,931 (64)	78.1 (78–78.3)	27.5 (27.5–27.6)
Has seen dietician – obesity	3,655	1,151 (31)	1,103 (30)	83.8 (82.6–85.1)	31.1 (30.6–31.5)
BMI high kg/m^2	81,453	37,107 (46)	64,334 (79)	85.9 (85.8–86)	30.8 (30.8–30.8)
Referral to weight management service declined	9,390	4,399 (47)	5,600 (60)	87.9 (87.3–88.4)	30.9 (30.8–31.1)
Weight symptom	96,442	20,969 (22)	56,428 (59)	89.1 (88.9–89.3)	32.6 (32.5–32.7)
O/E – overweight	7,971	2,353 (30)	4,370 (55)	92.2 (91.6–92.7)	33.1 (32.9–33.2)
Dietary advice for weight reduction	9,528	3,985 (42)	6,225 (65)	95.2 (94.7–95.7)	33.7 (33.6–33.9)
Obesity monitoring	69,543	15,231 (22)	44,339 (64)	96 (95.8–96.2)	35 (35–35.1)
BMI 30+ – obesity	100,687	42,312 (42)	61,734 (61)	96.8 (96.7–96.9)	34.5 (34.5–34.6)
Weight reducing diet	7,879	2,109 (27)	3,883 (49)	97.3 (96.6–97.9)	35.1 (34.9–35.4)
Patient advised to lose weight	6,388	2,743 (43)	4,418 (69)	97.3 (96.7–97.9)	34.5 (34.3–34.6)
Weight loss advised	85,248	32,717 (38)	56,094 (66)	97.5 (97.4–97.7)	34.7 (34.6–34.7)
Refer to weight management program	10,725	2,704 (25)	5,509 (51)	97.7 (97.2–98.3)	35.7 (35.5–35.8)
Follow-up obesity assessment	4,056	894 (22)	2,702 (67)	98 (97.1–98.8)	35.9 (35.6–36.1)
Obesity monitoring check done	4,603	1,421 (31)	1,545 (34)	98.1 (97.2–99)	35.5 (35.2–35.8)
Wants to lose weight	13,602	2,678 (20)	8,046 (59)	98.9 (98.5–99.4)	35.9 (35.8–36.1)
Weight management program offered	26,211	6,940 (26)	16,709 (64)	99.5 (99.1–99.8)	36.3 (36.2–36.4)
Patient advised to lose weight	24,865	10,871 (44)	14,806 (60)	99.8 (99.4–100.1)	35.2 (35.1–35.3)
Obesity monitoring NOS	1,624	393 (24)	741 (46)	101.3 (99.8–102.8)	36.5 (36–36.9)
Weight management plan started	7,953	2,116 (27)	5,350 (67)	102.1 (101.5–102.7)	37 (36.8–37.2)
Initial obesity assessment	2,584	764 (30)	945 (37)	103.8 (102.5–105.1)	37.2 (36.8–37.6)
Obesity	193,221	59,626 (31)	112,516 (58)	104.8 (104.7–104.9)	37.7 (37.7–37.7)
O/E – obese	4,172	1,361 (33)	2,414 (58)	106.1 (105.3–106.9)	38.1 (37.8–38.3)
BMI 40+ – severely obese	14,632	4,379 (30)	9,068 (62)	123.3 (122.9–123.7)	44.7 (44.6–44.8)
Morbid obesity	6,138	2,157 (35)	2,505 (41)	131.6 (130.7–132.5)	46.9 (46.6–47.2)

Abbreviations: kg, kilogram; BMI, body mass index; n, numerator; N, denominator; NOS, not otherwise specified; O/E, observation/examination.

Table 2 PPV of the most commonly used and specific abnormal weight codes

Abnormal weight code	Criteria for true positive	PPV (95% CI)
O/E – underweight	BMI <20	94.9 (93.7–95.9)
BMI <20	BMI <20	95.4 (94.1–96.5)
BMI low kg/m^2	BMI <20	81.3 (80–82.5)
BMI normal kg/m^2	BMI 20–24	91 (90.7–91.2)
BMI 20–24 – normal	BMI 20–24	96.9 (96.4–97.3)
BMI 25–29 – overweight	BMI 25–29	96.4 (96.1–96.7)
BMI high kg/m^2	BMI >25	99.3 (99.2–99.4)
O/E – overweight	BMI >25	99.6 (99.4–99.8)
Obesity monitoring	BMI >29	80.9 (80.5–81.2)
BMI 30+ – obesity	BMI >29	99 (98.9–99.1)
Follow-up obesity assessment	BMI >29	87.9 (86.6–89.1)
Obesity monitoring check done	BMI >29	94.4 (93.1–95.5)
Obesity monitoring NOS	BMI >29	91.3 (89.1–93.1)
Weight management plan started	BMI >29	92.7 (91.9–93.4)
Initial obesity assessment	BMI >29	95.5 (94–96.7)
Obesity	BMI >29	96.8 (96.7–96.9)
O/E – obese	BMI >29	98.8 (98.2–99.1)
BMI 40+ – severely obese	BMI >39	97.2 (96.8–97.5)
Morbid obesity	BMI >39	92.6 (91.5–93.5)

Abbreviations: BMI, body mass index; NOS, not otherwise specified; PPV, positive predictive value.

Figure 2 Comparison of the mean percent weight change estimated using three methods for each weight change code (hollow circles) and combined by weight change group (full circles).

Abbreviation: kg, kilogram.

Table 3 Internal validation of weight change Read codes using three methods of percent weight change estimation

Weight change code	Method of % weight change estimation
	Current vs last		Current vs predicted		Current vs mean
	N	Median (IQR)	N	Median (IQR)	N	Median (IQR)
[D]Abnormal loss of weight	13,126	−5.3 (−9.1 to −2)	8,641	−6 (−10.7 to −1.9)	13,189	−8.5 (−12.8 to −4.8)
Abnormal weight loss – symptom	21,603	−5.1 (−8.9 to −1.8)	14,007	−5.9 (−10.4 to −1.8)	22,448	−8.1 (−12.4 to −4.5)
Unintentional weight loss	168	−5.2 (−9.6 to −1.7)	109	−7 (−11.4 to −2.5)	152	−8.6 (−12.2 to −5.4)
Abnormal weight loss	1962	−4.7 (−9 to −1.1)	1,170	−5.8 (−10.8 to −1.6)	1910	−7.9 (−12.6 to −3.7)
Complaining of weight loss	5,397	−4.3 (−7.9 to −1.3)	3,773	−5 (−9.4 to −1)	5,702	−7 (−11.3 to −3.4)
Weight decreasing	7,089	−3.9 (−7.4 to −1.3)	4,419	−4.8 (−9.2 to −1.5)	6,881	−6 (−10.2 to −2.3)
O/E – cachexic	31	−3.6 (−10 to 0.2)*	13	−7.6 (−8.4 to −4.9)	15	−13.7 (−22.2 to −3.5)
Intentional weight loss	238	−3.9 (−7.6 to −1.5)	168	−5.4 (−9.7 to −2.8)	213	−5.1 (−8.8 to −1.5)
Cachexia	175	−2.9 (−7.2 to 0)*	48	−5.5 (−10.6 to −0.9)	73	−10.7 (−15.2 to −7.1)
Weight loss from baseline weight	3,013	−2.7 (−5.1 to −1.1)	2,465	−3.3 (−6.5 to −0.7)	3,058	−2.6 (−6.2 to 0.6)*
Pattern of weight gain	3	−0.4 (−7.1 to 0)*	2	2 (−6.4 to10.4)*	2	11.8 (9.7 to 14)
H/O: attempted weight loss	8	−1.7 (−4 to 0.2)*	8	−0.7 (−4.3to 6)*	9	−0.2 (−7 to 0.7)*
History of attempted weight loss	1,349	−0.5 (−3.9 to 2.5)*	1,031	−2.1 (−6.4 to 1.8)*	1,303	0.7 (−5.6 to 5.2)*
Weight symptom NOS	163	0 (−2.8 to 3.3)*	80	−1.4 (−6.1 to 2.4)*	137	0.3 (−4.8 to 4.3)*
Weight symptom	27,925	0.6 (−2 to 4)*	18,135	−0.1 (−4 to 4.2)*	27,385	2.4 (−2.2 to 7.3)*
Excessive weight gain in pregnancy	22	0.2 (−1.7 to 6)*	22	0.8 (−5.6 to 20.7)*	28	9.6 (−2.3 to 18)*
Weight increasing	9,401	2.9 (0.5–6.3)	5,831	3 (−0.4 to 7.7)*	8,601	5.9 (2.2–10.3)
Abnormal weight gain	8,210	4.2 (1.1–7.9)	4,782	3.9 (0–9.2)	7,876	7.8 (4–12.7)
Abnormal weight gain	346	4.4 (0.8–8.1)	215	4.6 (0.3–9)	354	7.9 (4.2–13.2)
Unintentional weight gain	1	7.1 (7.1–7.1)	1	12 (12–12)	1	2.6 (2.6–2.6)

Notes:

* Denotes the IQR incorporates 0. Orange shading denotes validated weight loss codes. Blue shading denotes weight symptom codes, which can be classified as neither weight gain nor weight loss codes. Green shading denotes validated weight gain codes.

Abbreviations: [D], diagnosis; H/O, history of; N, denominator; NOS, not otherwise specified; O/E, observation/examination.

Table 4 Weight change by weight change group, gender, and age group for each of the three methods of percent weight change estimation

	Method of % weight change estimation
	Current vs last		Current vs predicted		Current vs mean
	N	Mean (95% CI)	N	Mean (95% CI)	N	Mean (95% CI)
Weight loss	52,802	−5.2 (−5.2 to −5.2)	34,813	−5.4 (−5.5 to −5.3)	53,641	−7.9 (−8 to −7.8)
Male	21,785	−4.8 (−4.9 to −4.7)	14,048	−5.2 (−5.3 to −5.1)	22,292	−7.4 (−7.5 to −7.3)
Female	31,017	−5.4 (−5.5 to −5.3)	20,765	−5.6 (−5.8 to −5.4)	31,349	−8.3 (−8.4 to −8.2)
18–29 y	5,903	−5 (−5.2 to −4.8)	3,097	−5.2 (−5.7 to −4.7)	6,313	−6.3 (−6.5 to −6.1)
30–39 y	4,379	−4.9 (−5.1 to −4.7)	2,678	−5.4 (−5.9 to −4.9)	5,089	−6.5 (−6.7 to −6.3)
40–49 y	5,150	−5 (−5.2 to −4.8)	3,354	−5.2 (−5.5 to −4.9)	5,977	−6.8 (−7 to −6.6)
50–59 y	6,478	−4.9 (−5 to −4.8)	4,367	−5 (−5.3 to −4.7)	7,108	−7 (−7.2 to−6.8)
60–69 y	8,267	−5 (−5.1 to −4.9)	5,663	−5.2 (−5.4 to −5)	8,327	−7.7 (−7.8 to −7.6)
70–79 y	11,618	−5.3 (−5.4 to −5.2)	8,130	−5.7 (−5.9 to −5.5)	10,859	−8.9 (−9 to −8.8)
80+ y	11,007	−5.7 (−5.8 to −5.6)	7,524	−5.8 (−6 to −5.6)	9,968	−10.2 (−10.3 to −10.1)
Weight symptom	28,088	1 (0.9–1.1)	18,215	0.7 (0.6−0.8)	27,522	2.7 (2.6–2.8)
Male	6,628	0.1 (0–0.2)	4,120	−0.3 (−0.5 to −0.1)	6,537	0.9 (0.7–1.1)
Female	21,460	1.3 (1.2–1.4)	14,095	1 (0.8–1.2)	20,985	3.2 (3.1–3.3)
18–29 y	5,931	1.7 (1.5–1.9)	3,427	1 (0.6–1.4)	5,875	4.5 (4.2–4.8)
30–39 y	5,600	1.7 (1.6–1.8)	3,659	1.4 (1.1–1.7)	5,761	4.1 (3.9–4.3)
40–49 y	5,226	1.4 (1.3–1.5)	3,413	1.2 (0.9–1.5)	5,340	3.5 (3.3–3.7)
50–59 y	4,489	1 (0.9–1.1)	3,106	1.1 (0.8–1.4)	4,440	2.6 (2.4–2.8)
60–69 y	3,400	0.5 (0.3–0.7)	2,338	0.2 (−0.1–0.5)	3,126	1.4 (1.1–1.7)
70–79 y	2,162	−0.9 (−1.1 to −0.7)	1,448	−1 (−1.4 to −0.6)	1,896	−2.1 (−2.5 to −1.7)
80+ y	1,280	−3 (−3.4 to −2.6)	824	−2.3 (−3 to −1.6)	1,084	−6.7 (−7.2 to −6.2)
Weight gain	17,957	4.2 (4.1–4.3)	10,828	4.9 (4.7–5.1)	16,831	7.9 (7.8–8)
Male	4,006	3.3 (3.2–3.4)	2,473	4 (3.7–4.3)	3,707	6.4 (6.2–6.6)
Female	13,951	4.5 (4.4–4.6)	8,355	5.2 (5–5.4)	13,124	8.4 (8.3–8.5)
18–29 y	3,320	5.4 (5.2–5.6)	1,806	4.9 (4.4–5.4)	3,155	10.3 (10–10.6)
30–39 y	3,284	4.7 (4.5–4.9)	1,999	5.2 (4.7–5.7)	3,236	9.1 (8.8–9.4)
40–49 y	3,409	4.3 (4.1–4.5)	2,093	5 (4.6–5.4)	3,488	7.9 (7.6–8.2)
50–59 y	3,294	3.7 (3.5–3.9)	2,078	5 (4.6–5.4)	3,115	7 (6.8–7.2)
60–69 y	2,592	3.4 (3.2–3.6)	1,644	4.5 (4.1–4.9)	2,243	6 (5.7–6.3)
70–79 y	1,544	3.3 (3.1–3.5)	935	4.5 (4–5)	1,240	5.6 (5.2–6)
80+ y	514	3.3 (2.8–3.8)	273	5.4 (4.3–6.5)	354	4.9 (4–5.8)

Abbreviations: N, denominator; y, years.

Table 5 Association between time to previous weight measurement and estimated weight change

	Current vs last (%)
	N	Mean (95% CI)	Median (IQR)
Weight loss
0–2 w	3,278	−1.1 (−1.2 to −1)	−1.1 (2.9 to 0.3)
2–4 w	3,853	−2.3 (−2.4 to −2.2)	−2.1 (4 to −0.3)
1–2 m	5,401	−3.4 (−3.5 to −3.3)	−3.1 (5.5 to −1.1)
2–6 m	15,272	−4.9 (−5 to −4.8)	−4.7 (7.8 to −1.9)
6–12 m	13,572	−6.3 (−6.4 to −6.2)	−6.1 (9.9 to −2.7)
12–24 m	11,426	−7.2 (−7.3 to −7.1)	−7.1 (11.3 to −3.3)
Weight symptom
0–2 w	1,704	−0.3 (−0.4 to −0.2)	−0.1 (1.7 to 1)
2–4 w	2,209	−0.5 (−0.6 to −0.4)	−0.5 (2.2 to 1)
1–2 m	3,217	−0.3 (−0.4 to −0.2)	0 (−2.3 to 1.6)
2–6 m	8,331	0.5 (0.4–0.6)	0.6 (−2.2 to 3.4)
6–12 m	6,755	1.7 (1.5–1.9)	1.9 (−1.9 to 5.6)
12–24 m	5,872	2.4 (2.2–2.6)	2.7 (−1.8 to 7.1)
Weight gain
0–2 w	738	0.6 (0.4–0.8)	0 (−0.9 to 1.8)
2–4 w	923	1 (0.8–1.2)	0.8 (−0.9 to 2.5)
1–2 m	1,499	1.7 (1.5–1.9)	1.4 (−0.2 to 3.3)
2–6 m	5,552	3.4 (3.3–3.5)	2.9 (0.6 to 5.7)
6–12 m	4,983	5 (4.8–5.2)	4.6 (1.5 to 8.2)
12–24 m	4,262	6.6 (6.4–6.8)	6.2 (2.7 to 10.3)

Abbreviations: N, denominator; m, months; w, weeks.