How to assess kidney function in outpatient clinics.

Background: In 2002, a new definition and classification of chronic kidney disease was published, and glomerular filtration rate < 60 ml/min/1.73 m(2) for 3 months or more was adapted to define chronic kidney disease irrespective of other signs of kidney damage.

Aims: To discuss different ways to assess kidney function in outpatient clinics and especially in primary care.

Methods: The PubMed database was searched for relevant articles.

Results: The estimated glomerular filtration rate equations which take into account plasma creatinine, age, sex, race and body size have been developed to identify patients with chronic kidney disease formerly overlooked if the renal function had been assessed by plasma creatinine alone. Cystatin C-based equations have also been developed to enhance accuracy for individuals with whom creatinine-based estimates for kidney function are acknowledged to be less accurate.

Discussion: The characteristics of the patients to whom the diagnostic test is applied can influence the sensitivity of the test. Thus, there is nowadays controversy over the best method to assess kidney function in general population.

Conclusion: In the overwhelming majority of patients currently treated in primary care, the CKD-EPI creatinine equation is suitable for estimating renal function. The CKD-EPIcr-cys equation would provide further reliability in individuals with a CKD-EPI creatinine eGFR of 45-59 ml/min/1.73 m(2) , but the cost of serum cystatin C analysis limits its use in everyday general practice.