Discussion

In this descriptive study, we identified trends in test use for children from 2005 to 2019 in Oxfordshire by sex, age, and setting. Our results demonstrated that after an initial decline, testing rates for children appeared to increase from 2012 to 2019. Testing increases were more pronounced in females than males, and in children aged between 6 and 15 years compared with the other age groups. The largest relative increases occurred in the outpatient setting followed by general practice. The changes observed in overall testing rates can likely be attributed to testing increases in these settings and subgroups.

Of the most common tests, testing for vitamin D, parathyroid hormone, iron studies, folate and vitamin B₁₂ increased by the greatest proportion annually. Relative increases in these tests were most pronounced in general practice. These are consistent with temporal changes in test use by adults in UK primary care from 2000 to 2015,8 where O’Sullivan and colleagues reported increases in testing for vitamin D (which increased by 54% per year). Iron, ferritin, vitamin B₁₂ and folate testing in adults increased by 16–19% per year. In recent years, there has been greater awareness of vitamin D deficiency and iron deficiency, making it more likely that doctors will test for these conditions. Increased disease prevalence may also explain the rise in testing.14 Iron studies, folate, B₁₂, thyroid function tests, and creatine kinase form part of the workup for fatigue. A 2007 prospective study of British adolescents reported the point prevalence of fatigue was 38%, but more recent estimates are lacking.15 Most of these tests (vitamin D, iron studies, folate, vitamin B₁₂, coeliac test, serum IgA) are also included in investigations for malnutrition and faltering growth, suggesting increasing clinician concern and/or incidence of these conditions.

Testing rates in Oxfordshire decreased between 2005 and 2012 and then appeared to increase. Decreases in the early period mirrored decreasing inpatient and outpatient attendances at OUH.16 17 The inflection point in testing rates aligned with a major service change in 2011, when 11 new general paediatric consultants were appointed in Oxfordshire. While all staff were appropriately qualified, newer members of staff may have been inclined to test more,18 19 which may be one explanation for change in trends in testing rates. In addition, parental expectations and anxiety levels have increased. In primary care, there has been a decline in experienced family doctors who are more likely to reassure parents without testing and referring children, and a concurrent rise in less experienced GPs who may test and refer more.20 Parents of children referred by these GPs may present to outpatient appointments expecting a diagnostic workup.

The most pronounced increases in testing occurred in the outpatient setting, which expanded during the study period. According to NHS digital data, from 2009 to 2020, the number of children seen in OUH outpatient clinics increased by 63% (with a sharp increase in 2013).16 Since the Oxford Children’s Hospital opened in 2007, the tertiary specialty workload has grown, with an increased number of referrals from all around the region outside of Oxfordshire (including Berkshire, Buckinghamshire, Wiltshire, Milton Keynes). We could not distinguish between tests that were conducted among Oxfordshire residents and referrals for tests from other areas, or which tests were for specialty or general paediatric patients. As a result, the appropriateness of the denominator may have changed over time, influencing the observed trends.

Some of the observed increases in testing rates warrant further investigation as to their appropriateness. The National Institute for Health and Care Excellence guidance only recommends vitamin D testing in children if they have musculoskeletal symptoms, abnormal serum bone profile or X-ray findings, suspected bone disease such as osteomalacia, or known bone disease such as osteoporosis.21 A retrospective analysis of vitamin D testing in the Northumbria Healthcare NHS Trust from 2002 to 2017 found that over 75% of the tests performed on those aged below 30 had an inappropriate clinical indication.22

The clinical implications of these reported trends should be considered on a test-by-test basis. Our findings of vitamin D testing trends mirror those of a recently published study from Australia, which reported that vitamin D test requests for children increased 30-fold in general practice from 2003 to 2018 with the odds of detecting low levels remaining stable.23 The incidence of nutritional rickets in children (the sequelae of vitamin D deficiency) was also reported to be low, with an annual incidence of 0.48 per 100,00 children under 16 in a UK-based surveillance study from 2015 to 2017,24 reinforcing the need to mitigate this low-value practice. Instead, for asymptomatic children, routine supplementation could be considered rather than testing. Comparing testing rates with rates of abnormal tests for ferritin, B₁₂ and folate would help to assess whether this represents low-value testing. We did not conduct such analyses because information on past laboratory analytical methods and reference ranges was unavailable. Efforts to reduce unnecessary tests should also target specific settings based on the observed trends, for instance, haematinics in general practice.

Unnecessary testing in children has important cost implications. Assuming the cost of a vitamin D test was £10 (OUH NHS Trust laboratory price), expenditure on vitamin D tests for children in Oxfordshire in 2019 was £37 900. In UK primary care alone, an estimated £1.7 million was spent on vitamin D tests on children aged 0–17 years in 2014.25 Given the subsequent increases in vitamin D testing, it is likely that current national expenditure on vitamin D tests in children is far higher than this figure across primary and secondary care. The financial consequences of unnecessary tests also extend beyond the cost of tests alone; tests generate increased workload for laboratory staff as well as the clinicians who must review and action the result. An abnormal result often leads to further investigation and monitoring, treatment and/or referrals, which also costs the health system.

Our study is the first to describe long-term trends in test use in a population-based study of children. One limitation is that we did not have individual patient-level data containing clinical indications for each test, preventing further analysis exploring the appropriateness of tests against existing clinical guidelines. If patient-level data were available, sensitivity analyses excluding children with high testing rates (ie, those who have complex conditions or frequently visit hospital) would provide a more accurate view of trends in testing for the general population.

The generalisability of our findings beyond Oxfordshire is unclear. Oxfordshire, on average, is a less socially deprived region with high educational attainment, and our results of increased test use over time may reflect greater access to laboratory tests in this area. These findings should be compared with other settings to examine if the changes in test use are consistent across England and in other places with similar paediatric healthcare systems. Individual patient-level data including demographics could be used to determine if testing rates are linked to deprivation levels and ethnicity.

We limited testing data until the end of 2019 to eliminate the impacts of the COVID-19 pandemic, during which diagnostic testing decreased substantially.26 The pandemic could serve as a natural experiment, allowing us to examine the impacts of decreased healthcare utilisation. More recent data would also allow us to examine how testing rates recovered following the pandemic, in response to the subsequent increase in healthcare presentations.

Further analyses of testing variation could also include other tests, including urine testing, microbiology and infection, imaging, and spirometry.