Chronic renal failure (U99)

March 3, 2023
Clinical course of chronic renal failure (CRF)

An important function of the kidney is to excrete waste products by (glomerular) filtration and / or secretion. The kidney function is estimated by calculating the glomerular filtration rate (eGFR). The eGFR is calculated with the CKD-EPI formula which includes sex, age, body size and the level of circulating creatinine. The renal function shows a physiologic decline with increasing age. Chronic renal failure (CRF) is defined by a persisting (more than three months) decrease of the glomerular filtration rate (eGFR <60 ml/min/1,73m2) and / or albuminuria (albumin / creatinine ratio >3 mg/mmol) and / or abnormalities in the urinary sediment (e.g. dysmorphic erythrocytes or erythrocyte cylinders).

Clinical symptoms of chronic renal failure may occur in more severe cases of renal failure and are not frequently seen in general practice. In CRF with an eGFR below 30 ml/min/1,73m2 patients may present with metabolic complications such as anaemia, itch, gout, acidosis and gastrointestinal symptoms (e.g. nausea, decreased appetite).

Common causes of CRF are hypertension, type 2 diabetes mellitus, and atherosclerotic vascular disease. Specific (familiar) renal diseases may also cause CRF.

A decreased eGFR and increased albuminuria are independent risk factors and predictors in themselves of (cardiovascular) mortality, the (acute) progression of CRF and of end stage renal failure (eGFR <15 ml/min/1,73m2).

In the diagnosing and staging of CRF, the GP assesses the eGFR, the albumin-creatinine ratio in the urine, and the cardiovascular risk profile. Treatment consists of optimising the cardiovascular risk profile and reducing the risk of progression of CRF. RAS-inhibitors are the preferred antihypertensives in the case of albuminuria. Nephrotoxic medication is best avoided. To support safe prescribing in patients with CRF, an alert should be created in the Electronic Health Record that CRF is present, so that medication monitoring systems can warn for nephrotoxic medication or when medication dosage needs to be adjusted.

How is chronic renal failure recorded in FaMe-Net ?

Chronic Renal Failure is coded with the ICPC code U99, ‘other urinary disease’. CRF is the most important condition coded U99, although some other (less common) diseases of the urinary tract are also coded U99, mainly acquired / anatomical abnormalities of the urological system (for example, vesico-ureteral reflux, hydronephrosis, renal cysts and neurological bladder dysfunction). In this FaMe-Net dataset, based on the ICPC classification, CRF cannot be distinguished from other conditions recorded with U99. For research specifically focussing on CRF, it would be possible to make an extraction of data that includes the additional ICD-10 classification, which refers only to ‘chronic renal failure’.

Epidemiology of chronic renal failure in FaMe-Net

The incidence of CRF is 4.6 per 1000 patient years, meaning five new diagnoses per 1000 patients in a year across all age groups. CRF occurs mainly among elderly patients, with incidence numbers increasing from the age of 65 onwards. This is explained by the main aetiological factors for CRF: ageing and cardiovascular diseases. In the age group 45-64, the incidence is 16.3, and in the age group 75+, the incidence is 43.9 per 1000 patient years. Link/Figure 1

The prevalence of CRF is 11.6 per 1000 patient years, meaning that among 1000 patients in a year, 12 patients seek help from their GP for CRF. Prevalence increases with age from 45 years of age onwards. Most patients contacting their GP for CRF are older than 75 years. The prevalence is equal between men and women. Link/Figure 2

Among patients aged 75 and older, CRF is ranked as the ninth most common condition for which patients consult their GP. Link/Table 3

Which initial RFEs do patients with chronic renal failure present to their GP?

CRF initially presents as being asymptomatic. This is reflected by the recorded Reasons for Encounter (RFEs) for CRF. Link/Table 4 Most episodes (69%) start with an administrative RFE (*62) which means that the episode starts with a note or letter, for instance, a laboratory test result following routine control for other conditions such as hypertension or diabetes, or a (specialist) letter reporting the CRF, which may have been an occasional finding. The other commonly reported RFEs also indicate that CRF presents without specific symptoms, for example, as a request for a test result (*60), after initiation by the GP (*64) or someone else (*65) or as a request to perform a control (*31) or a test (*34 and *35). Renal failure itself (U99) as an RFE (in 5% of all episodes) is probably the result of testing or screening elsewhere. Urinary frequency (U02) as initial RFE is also reported for episodes U99, but probably mostly concerns ‘other diseases’ than CRF.

How do FaMe-Net GPs act?

Therapeutic and preventative actions aimed at optimising the risk of CRF will often be reported under the episode of conditions co-occurring with CRF, such as type 2 diabetes (T90), hypertension (K86) or other vascular conditions. This means that many interventions related to renal failure will be recorded elsewhere and that the numbers of interventions mentioned below do not give a complete overview of GPs’ actions as part of the management of CRF. For research purposes, it is possible to make an extraction of individual patients with CRF to assess the occurrence of prescriptions (or other interventions) in any episode, i.e. including those reported under episodes other than U99. Additional data are available upon request.

Commonly reported interventions for CRF (U99) are blood tests (*34), the prescription of medication (*50) and health education (*45). GPs consult a specialist (*47) in 4% of all episodes of CRF per year. The consulted specialisms cannot be distinguished from this dataset, but they will mostly concern nephrologists. Referral to a specialist (*67) occurs in 6% of episodes annually. Link/Table 5 This involves specialists in internal medicine (nephrologists), in 3% of all episodes with ICPC code U99, urologists, in 2% and, very rarely (less than 1% of episodes), other specialists. Link/Table 6 The above referrals to urologists most likely concern referrals for diseases other than CRF but which are also coded U99. The opportunity for GPs to consult a nephrologist for advice (instead of making a referral) facilitates CRF to be managed mainly in primary care, which is also reflected in the low rate of referrals to a nephrologist. Looking at a selection of patients aged 65 years and above shows that with increasing age, the occurrence of ‘consultation of a specialist’ (*47) starts to favour ‘referral to a specialist’ (*67). Link/Table 7

The most prescribed medication types for CRF are vitamin D analogues. The prescription of medication in FaMe-Net is always linked to one episode (and cannot be linked to multiple episodes). As explained above, prescriptions for CRF will often be reported under co-occurring conditions. Some common prescriptions for CRF, such as RAS-inhibitors, are underreported in the overview of prescriptions for episodes of U99. Link/Table 8 Medication classes such as urogenital antispasmodics (G04BD) or alfa-adrenoreceptor antagonists (G04CA) are reported under the ICPC code U99 but concern ‘other diseases’ and not CRF.