Effectiveness of professional and patient-oriented strategies in reducing vitamin D and B12 test ordering in primary care: a cluster randomised intervention study

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Figure 1. Flow diagram of the study and its participating health centres
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Figure 2. Number of ordered vitamin tests in pre-intervention period (in quartiles) related to reduction in number of ordered tests during intervention period. pts = patients.

Table 1. Baseline characteristics of participating GPs, including pre-intervention numbers of vitamin testing

Characteristic	Total	Intervention group
Strategy 1(GP only)	Strategy 2(GP and patient)	P value
Health centres, n	26	13	13
GPs,n	158	78	80	0.85
Male, n (%)	47 (30)	25 (32)	22 (28)	0.72
Population, n	195 394	97 658	97 736	0.99
SES, mean (range)^a	0.26(−2.58–2.06)	0.53(−2.40–2.06)	0.21(−2.58–1.66)	0.48
Vitamin D tests pre-intervention, n	17 527	10 277	7250	0.30
Vitamin D/1000 patients pre-intervention, n (range)	88 (12–262)	102 (32–262)	75(12–150)	0.22
Vitamin B12 tests pre-intervention, n	12 304	7242	5062	0.36
Vitamin B12/1000 patients pre-intervention, n (range)	59 (7–198)^b	69 (7–198)	49 (15–156)	0.21
GPs who followed e-learning, n (%)	76 (48)	28 (36)	48 (60)	0.11
GPs present at first training session, n (%)	50 (32)	26 (33)	24 (30)	0.86
GPs present at second training session, n (%)	50 (32)	24 (31)	26 (33)	0.85

^aSES data, linked by four digital postal codes to location of health centre.¹⁷ ^bMean difference Utrecht-Rotterdam = –60 (95% CI = –94 to –26), P = 0.06. SES = socioeconomic status.

Table 2. Reduction in number of vitamin D and B12 tests

Characteristic	Total	De-implementation strategy
Strategy 1 (GP only)	Strategy 2 (GP and patient)
Health centres, n	26	13	13
Vitamin D
Reduction, % (range)	23(−9–70)	19(−4–70)	29(−9–28)
Absolute reduction in vitamin D/1000 patients, mean (range)	22 (−6–98)	24 (−6–98)	21 (−6–51)
Vitamin B12
Reduction, % (range)	20(−19–63)	18(−3–63)	22(−19–42)
Absolute reduction in vitamin B12/1000 patients, mean (range)	12 (−6–69)	15 (−3–69)	9 (−6–63)

Table 3. Results of ordered vitamin D and B12 tests