Overview of the CRP test frequency
During the 15-year period, 91 540 CRP tests were requested in 63 226 children; 52 947 tests (57.8%) in 33 882 children in primary care and 38 593 (42.2%) tests in 29 344 children in A&E (table 1; 5604 (8.9%) children had tests in both primary care and A&E over the study period). In children with more than one test, the median test frequency per child in primary care was 2 (2–3) with a median duration of 458 days (117–1060) between the tests (8348 children; 24.6%), whereas the median test frequency per child in A&E was 2 (2–3) with a median duration of 180 days (13–726) between the tests (5683 children; 19.4%).
CRP test frequency per age group at different settings and their CRP test results
CRP test in primary care
In primary care, the annual distribution of the test requests increased progressively over the study period, from 2459 test requests in 2007 to 3958 in 2021 with an AAPC of 3.0% per year (95% CI 1.2% to 4.7%, p=0.001) (figure 1). Notably, there was an evident APC increase of 6.0% per year (95% CI 4.0% to 8.1%, p<0.001) from 2007 to 2016. Subsequently, between 2017 and 2021, there was no evidence of change in APC (change of −2.3% per year, 95% CI −6.3% to 1.8%, p=0.235) but there was substantial variability driven by the COVID-19 pandemic (figure 1). Moreover, the increase was mainly in tests with low CRP values, with an APPC of 3.3% per year (95% CI 1.6% to 5.0%, p<0.001) (figure 2). However, the number of tests with intermediate and high CRP values decreased significantly throughout the entire study, with an AAPC of −4.1% per year (95% CI −6.7% to −1.5%, p=0.005) and −5.8% per year (95% CI −9.9% to −1.5%, p=0.009), respectively (figure 2). There was no evidence of change in hospital referrals (figure 3).
Annual percentage change in CRP test requests in primary care. *Indicates that the annual per cent change (APC) is significantly different from zero at the alpha=0.05 level. Final selected model: 1 Jointpoint. CRP, C reactive protein.
Distribution of CRP test results throughout the study period in primary care. *Indicates that the annual per cent change (APC) is significantly different from zero at the alpha=0.05 level. CRP, C reactive protein.
Distribution of hospital referral decision in tested children (regardless of CRP value) at primary care. CRP, C reactive protein.
Most tests were requested in adolescents (32 537 (61.5%)) and primary school children (17 366 (32.8%)), with these groups accounting for 95.3% and 96.9% of the CRP values <20 mg/L, respectively (table 1). In younger children, most test results (92.6%–94.6%) were also <20 mg/L (table 1).
In terms of referral patterns, following tests with CRP<20 mg/L almost all children (99.0%) were managed at home, whereas children with test results ≥80 mg/L were more likely to be referred to A&E (n=38, 10.1%) or directly admitted (n=30, 8.0%) (figure 4). While high CRP value was associated with substantially increased odds of referral compared with low CRP values (OR adjusted for age group=21.80; 95% CI 16.49 to 28.81), as were intermediate CRP values to a lesser degree (OR adjusted for age group=4.77; 95% CI 3.78 to 6.02) (table 2).
Association between CRP value with hospital referrals at primary care and discharge decision at A&E departments, adjusted for age
Referral flow from primary care to other healthcare settings within 48 hours from each CRP test result, based on CRP level. 50 706 (95.8%) tests were <20 mg/L, 1861 (3.5%) tests were ≥20 and <80 mg/L, and 376 (0.7%) tests were ≥80 mg/L. A&E, accident and emergency; CRP, C reactive protein.
In the 437 admitted children from this group, the most frequent primary diagnosis was unspecified abdominal pain (n=50, 11.5%), Crohn’s disease (n=23, 5.3%), appendicitis (n=19, 4.4%) and lower respiratory tract infections (LRTI) with unspecified causative organisms (n=11, 2.5%).
CRP test at the A&E departments
In the A&E departments, the annual distribution of the test requests showed a substantial increase throughout the study period, climbing from 8 test requests per 100 visits in 2007 to 23 test requests per 100 visits in 2021, with an AAPC of 9.9% per year (95% CI 7.5% to 12.4%, p<0.001) (figure 5). Specifically, the APC of test requests increased by 16.4% per year (95% CI 11.5% to 21.5%, p<0.001) from 2007 to 2014, and then slowing to a more modest APC of 3.7% per year (95% CI 1.0% to 6.6%, p=0.013) between 2014 and 2021 (figure 5).
Annual percentage change in CRP test requests at A&E departments. *Indicates that the annual per cent change (APC) is significantly different from zero at the alpha=0.05 level. A&E, accident and emergency; CRP, C reactive protein.
Regarding test results, all groups saw increasing AAPC: low CRP values by 11.8% (95% CI 9.2% to 14.5%, p<0.001), intermediate CRP values by 12.4% (95% CI 8.2% to 16.6%, p<0.001) and high CRP values by 10.1% (95% CI 6.5% to 13.8%, p<0.001). Specifically, low CRP values rose annually by 21.8% (95% CI 16.5% to 27.4%, p<0.001) from 2007 to 2014, and by 2.6% (95% CI −0.3% to 5.6%, p=0.071) from 2014 to 2021. Intermediate and high CRP values initially increased at rates of 23.5% (95% CI 17.5% to 29.7%, p<0.001) and 19.9% (95% CI 15.0% to 25.1%, p<0.001) annually from 2007 to 2016, respectively, but then declined at rates of −5.2% (95% CI −12.4% to 2.7%, p=0.167) and −5.6% (95% CI −12.2% to 1.6%, p=0.111) annually from 2016 to 2021, respectively (figure 6).
Distribution of CRP test results throughout the study period at A&E departments. *Indicates that the annual per cent change (APC) is significantly different from zero at the alpha=0.05 level. Final selected model: 2 Jointpoints. A&E, accident and emergency; CRP, C reactive protein.
Similarly to primary care, the greatest proportion of test requests was also observed in adolescents (13 158 (34.1%)) and primary school children (11 210 (29.1%)), with these groups accounting for 77.9% and 70.5% of the CRP results <20 mg/L, respectively (table 1). Similarly, most test results in the younger children (61.3 and 74.3%) were also <20 mg/L (table 1).
Following test results with CRP<20 mg/L in this setting, 42.5% of children (n=11 730) were admitted to the hospital, compared with 57.9% (n=2188) of children with CRP test results ≥80 mg/L (figure 7). High CRP value nearly doubled the admission odds compared with low CRP value (OR adjusted for age group=1.90, 95% CI 1.78 to 2.04) with a smaller effect of intermediate CRP value (OR adjusted for age group=1.39, 95% CI 1.32 to 1.46) (see table 2). The overall admission rate fluctuated throughout the study, starting with a gradual rise and subsequently stabilising (figure 8).
Referral flow from A&E departments to admission or home within 48 hours from each CRP test result, based on CRP level. 27 604 (71.5%) tests were <20 mg/L, 7207 (18.7%) tests were ≥20 and <80 mg/L, and 3776 (9.8%) tests were ≥80 mg/L. A&E, accident and emergency; CRP, C reactive protein.
Distribution of discharge decision in tested children (regardless of CRP value) at A&E. A&E, accident and emergency; CRP, C reactive protein.
The most frequent primary diagnosis among admitted children from this group was unspecified abdominal pain (n=2054, 11.8%), appendicitis (n=1276, 7.3%), upper respiratory tract infections of unspecified organism with unspecified causative organisms (n=997, 5.7%) and LRTI with unspecified causative organisms (n=774, 4.4%). Notably, the proportion of low CRP values was relatively high in abdominal pain and appendicitis (83.2% and 42.3%, respectively). Correspondingly, these diseases exhibited lower percentages of intermediate CRP values (12.1% and 31.1%, respectively) and high CRP values (4.7% and 26.6%, respectively).
This post was originally published on https://bmjopen.bmj.com