The prevalence and identification of chronic kidney disease in Switzerland

BACKGROUND: Chronic kidney disease (CKD) is characterized by a gradual loss of kidney function. Patients in early CKD stages are often asymptomatic or show non-specific symptoms. Therefore many cases of CKD are identified only in more advanced and symptomatic stages. The most common risk factors of CKD are hypertension, diabetes, and older age. CKD is usually defined and diagnosed by using the glomerular filtration rate (GFR) and the albuminuria (or the albumin-to-creatinine ratio, ACR). Another marker of renal diseases is the neutrophil gelatinase-associated lipocalin (NGAL). The epidemiology of CKD has been investigated in several countries and settings. However the information concerning the CKD prevalence in primary care in Switzerland and in general in Europe is still scarce. The goal of this work was to estimate the prevalence of CKD in a primary care setting in Switzerland, to investigate NGAL as possible biomarker of renal disease, and to shortly review the relationship between NGAL and acute kidney injury (AKI) as well as between AKI and CKD. METHODS: A cross-sectional, multicentre, non-interventional study was conducted in seven Swiss cantons. Adult patients visiting the randomly selected general practitioners during defined periods were asked to participate. Emergency patients were excluded. Demographic and social variables, clinical status and co-morbidities were reported on a questionnaire. Urine and blood samples were sent to a central laboratory for analysis. CKD was assessed by creatinine-based estimates of the glomerular filtration rate (eGFR), calculated with the CKD-EPI equation, and by albumin creatinine ratio (ACR). All patients were stratified into CKD stages using the KDIGO classification. Extrapolation of CKD prevalence in primary care to national level was based first on the number of patients older than 15 years of age who had visited a GP at least once in 2007, as reported by the Swiss Federal Statistical Office (FSO). The calculations were adjusted for age and gender distributions. The relationship between NGAL and AKI as well as between AKI and CKD has been discussed on the basis of the recently published literature. RESULTS: The Prevalence of Chronic Kidney Disease in a Primary Care Setting: a Swiss Cross-Sectional Study: Among the 1'000 individuals recruited, 57% were female, and the mean age was 57±17 years. Overall, 41% of the patients had normal eGFR and ACR, whereas 36% of the subjects had slightly reduced eGFR with normal ACR. Almost one fourth of the subjects (23%) had either a substantially reduced eGFR or high levels of ACR. About 10% of the patients had a substantially reduced eGFR of 30 mg/g creatinine). At primary care level, the prevalence of CKD has been estimated to be at 19%. Extrapolation to national level suggested that about 11% of all subjects older than 15 years in Switzerland may suffer from CKD. Insights on urinary NGAL obtained in a primary care setting: The same population sampling mentioned above showed a median absolute uNGAL of 21 ng/L. Elevated uNGAL (>100 ng/L) together with normal kidney test results (eGFR and ACR) were found in 6.5% of all patients. Females had a significantly higher uNGAL than did males. When examining the proposed KDIGO classification of CKD, the uNGAL levels at the given eGFR stages changed with increasing ACR stages and vice versa. CONCLUSIONS: The prevalence of impaired renal function and/or CKD in Switzerland is considerably high. Based on the data provided by the Swiss FSO, it may be reasonable to assume that the prevalence of CKD may grow up in the next decades, according to the increasing prevalence of its major risk factors (i.e. diabetes, hypertension, and older age). Prevention in form of healthy lifestyle and consequently reduced risk for CKD, and early recognition of CKD are important in order to slow or prevent progression to severe and symptomatic stages. In this optic, an increase in the CKD awareness among clinicians and patients is fundamental. Concerning NGAL, despite the fact that there is general agreement that it is significantly correlated with serum creatinine and eGFR, there is not yet enough evidence concerning its predictive potential for progressive CKD. In particular it is not yet clear if adding an NGAL test to the classical prognostic factors for CKD (eGFR, albuminuria, age, gender, BMI, hypertension and diabetes) will substantially improve the prediction of outcome events in CKD patients. Recent studies suggested that CKD and AKI may be two closely interconnected conditions. Indeed, each condition can be considered as risk factors for the other, and both diseases are risk factors for cardiovascular diseases. Elevated NGAL values have been associated with both diseases and seem to support their interconnection. Several studies reported that NGAL may be useful alongside serum creatinine, urine output, and other biomarker for the diagnosis and prognosis of patients with CKD or AKI. Unfortunately the validity of these results is limited to the specific settings and samplings. It is therefore premature to implement NGAL testing in the routine clinical use.