Introduction

Kidney function testing in primary care is used to diagnose and monitor chronic kidney disease (CKD). Testing is recommended at baseline and after initiation of some drugs such as antihypertensives.1 Kidney function is usually tested by measuring serum creatinine, and screening for glomerular disease is undertaken by measuring urine albumin or protein concentrations.

In 2002, the Kidney Disease Outcomes and Quality Initiative (K/DOQI) published clinical guidelines advocating that CKD be categorised into five stages.2 Two years later, these stages were adopted by the UK Quality and Outcomes Framework (QOF), which is a set of business rules for primary care that include financial incentives to regularly monitor and test certain subsets of patients and to record their data.3 The 2006–2007 financial year saw an extension to QOF that required general practitioners to maintain a register of patients with CKD stages 3–5.4 In 2008, the National Institute for Health and Care Excellence (NICE) recommended monitoring estimated glomerular filtration rate (eGFR) levels in high-risk patients.5 Then in the 2009–2010 financial year, a further QOF extension incentivised monitoring urinary markers of kidney disease (such as proteinuria) in patients on the CKD register.6 Current NICE recommendations on the frequency of testing are based on the underlying cause of CKD, previous test results, comorbidities and the treatments being used. Monitoring is recommended annually in patients with mild to moderate reductions in kidney function and every three months in patients with more advanced disease.1

National rates of kidney function testing and potential differences between different populations have not been characterised. In contrast, rates of kidney function testing in patients with diabetes have been well documented. A cohort study of adults with diabetes showed that under 13% had incomplete CKD screening, and just 4.4% had no serum creatinine measurement on record in the two and half years before the start of the study, whereas the albumin-creatinine ratio (ACR) was not monitored in 37% during the same period.7 Similarly, high frequencies of serum creatinine testing have been observed among patients with diabetes in studies looking at individual health regions, but with more variable levels of recording in patients without diabetes across different ages, genders and ethnic groups.8

There has been a dramatic increase in the use of laboratory testing over recent decades, particularly repeated testing or monitoring.9 10 However, it is unclear whether this increase is appropriate and consistent with guideline recommendations or whether it represents overtesting. Appropriate testing of kidney function might be of value in planning management to slow the progression of the disease and, therefore, lead to tangible patient benefit. However, overuse of tests provides little patient benefit and adds to the financial burden of healthcare systems. A recent meta-analysis of the use of laboratory tests during the last 15 years showed that underuse of high-volume tests (such as creatinine) was more likely than overuse.11 A cross-sectional survey of US physicians’ patterns of care in patients with CKD showed that 85% of physicians recommended one additional test, which was not recommended in the Kidney Disease Improving Global Outcomes (KDIGO) guidelines.12 These tests were most likely to be magnetic resonance angiography of renal arteries or serum protein electrophoresis, rather than blood or urinary measurements.13 It is, of course, possible that overuse and underuse may coexist, with some patients receiving more tests than indicated and other patients not receiving tests warranted by their clinical history, recent health and age.

Currently, the UK is the only nationalised and publicly funded health service that has introduced financial incentives to improve the quality of healthcare for patients with CKD. National guidelines in other countries also recommend quality standards for CKD care, including diagnosis, monitoring of renal function and control of cardiovascular risk factors.14 However, guideline bodies outside the UK have stopped short of implementing financial incentives for CKD care, and therefore, studying the impact of QOF in the UK can inform international efforts to improve outcomes for patients with CKD.

The aim of this study is to describe rates of kidney function testing since the introduction of the QOF in UK general practice. Specifically, we have examined the numbers of serum creatinine and proteinuria tests requested in each financial year during the nine years from 2005 to 2013 by: age category, gender, ethnicity, index of multiple deprivation (IMD), Strategic Health Authority (SHA), CKD stage, the presence or absence of major comorbidities (such as diabetes, hypertension, cardiovascular disease and atrial fibrillation) and the prescription of nephrotoxic drugs.