C-reactive protein cut-offs used for acute respiratory infections in Danish general practice

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Figure 1. C-reactive protein (CRP) levels and the proportion of patients prescribed an antibiotic. Legends indicate the width of the interval around the index CRP level used to calculate the proportion of patients who were prescribed antibiotics, respectively 0, 5, and 10mg/L above and below. Bars indicate 95% confidence intervals. CRP levels 150–300mg/L not shown.
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Figure 2. Proportions of patients who are prescribed an antibiotic according to C-reactive protein (CRP) levels in the range from 5 mg/L below to 5 mg/L above the index. CRP levels 100–300 mg/L not shown.

Table 1. Characteristics of the 143 participating GPs compared to all GPs in each regions.

Table 2. C-reactive protein (CRP) tests for patients with acute respiratory tract infections in Danish general practice

Patient characteristics	Total	CRP POCT performed	Odds of CRP POCT
n (%)	n (%)	OR_age-adjusted (95% CI)
Total	7832 (100)	4635 (59)
Age groups, years
0–14	2705 (35)	772 (29)	1 (reference)
15–64	3793 (49)	2773 (73)	6.81 (6.10 to 7.60)
>64	1305 (17)	1071 (82)	11.46 (9.72 to 13.51)
Symptoms and findings
Fever	2971 (38)	1811 (61)	1.81 (1.62 to 2.02)
Cough	5611 (72)	3714 (66)	2.85 (2.54 to 3.20)
Sore throat	1866 (24)	1053 (56)	0.78 (0.69 to 0.88)
Ear/face pain	1317 (17)	592 (45)	0.54 (0.47 to 0.62)
Dyspnoea	881 (11)	691 (78)	1.97 (1.63 to 2.36)
Purulent rhinorrhoea	1324 (17)	714 (54)	0.83 (0.72 to 0.94)
Deterioration of symptoms	861 (11)	569 (66)	1.34 (1.13 to 1.58)
Poor general appearance	1546 (21)	1131 (73)	2.15 (1.87 to 2.47)
Abnormal lung auscultation	1063 (14)	765 (72)	1.67 (1.42 to 1.97)
Duration of symptoms, days
≤1	504 (7)	193 (38)	1 (reference)
2–4	2958 (40)	1551 (52)	1.35 (1.09 to 1.68)
5–14	3233 (44)	2134 (66)	1.85 (1.49 to 2.30)
>14	679 (9)	470 (69)	1.60 (1.22 to 2.09)

CI = confidence interval. CRP = C-reactive protein. OR = odds ratio. POCT = point-of-care test

Table 3. C-reactive protein (CRP) cut-offs^a used by 143 Danish GPs for patients with acute respiratory tract infections

Patient characteristics	25% cut-offCRP, mg/L (CI)	50% cut-offCRP, mg/L (CI)	75% cut-offCRP, mg/L (CI)
All the patients (n = 4635)	20 (18 to 22)	40 (37 to 42)	50 (47 to 98)
Age group, years
0–14	22 (18 to 67)	43 (32 to 98)	45 (43 to 98)
15–64	22 (20 to 28)	42 (38 to 45)	64 (49 to 99)
>64	17 (14 to 20)	33 (24 to 41)	46 (41 to 98)
Fever
Yes	20 (17 to 23)	38 (34 to 41)	47 (45 to 84)
No	22 (17 to 25)	45 (36 to 97)	66 (50 to 99)
Symptoms
Cough	24 (22 to 27)	42 (38 to 44)	64 (49 to 99)
Sore throat	29 (19 to 37)	45 (38 to 71)	74 (49 to 99)
Ear/face pain	11 (5 to 12)	20 (14 to 99)	40 (37 to 99)
Dyspnoea	11 (8 to 20)	24 (21 to 99)	38 (30 to 99)
Purulent rhinorrhoea	14 (13 to 32)	38 (25 to 99)	55 (40 to 99)
Duration of symptoms, days
≤1	21 (14 to 89)	29 (22 to 99)	53 (29 to 99)
2–4	24 (20 to 36)	43 (41 to 48)	54 (49 to 98)
5–14	17 (15 to 22)	38 (33 to 61)	46 (45 to 99)
>14	15 (14 to 93)	27 (21 to 93)	50 (29 to 93)
Deterioration of symptoms
Yes	14 (11 to 39)	42 (20 to 99)	46 (42 to 99)
No	22 (20 to 24)	41 (37 to 44)	51 (49 to 98)
Poor general appearance
Yes	15 (11 to 17)	29 (22 to 41)	44 (42 to 85)
No	24 (21 to 29)	43 (39 to 46)	66 (51 to 99)
Abnormal lung auscultation
Yes	3 (1 to 8)	22 (13 to 27)	32 (28 to 99)
No	24 (21 to 33)	45 (42 to 62)	68 (50 to 99)

^aEstimated as the lowest level of CRP at which the given percentage of patients were prescribed an antibiotic. Values in brackets indicate the 95% CI for the CRP levels ±5 mg/L, based on binomial distribution. CI = confidence interval. CRP = C-reactive protein.