24th June 2023

Classification of chronic kidney disease

Chronic kidney disease (CKD) is defined as a persistent reduction in renal function (for greater than three months); this may be progressive in nature and have consequences for patient health. Classification of CKD is based on glomerular filtration rate (GFR), amount of albuminuria and underlying cause.

GFR categories

Table 1: Staging of CKD based on GFR, adapted from the KDIGO 2012 Clinical Practice Guideline for the ‘Evaluation and Management of Chronic Kidney Disease’ and the NICE guideline on ‘Chronic Kidney Disease: Assessment and Management’.

Albuminuria categories

Table 2: Staging of CKD based on albuminuria, adapted from the KDIGO 2012 Clinical Practice Guideline for the ‘Evaluation and Management of Chronic Kidney Disease’ and the NICE guideline on ‘Chronic Kidney Disease: Assessment and Management’

It is important to note factors that may influence the interpretation of the measurements above, for example, those of particularly high muscle mass or lower than expected muscle mass (e.g. amputees, muscle wasting disorders). It is normal for GFR to gradually decline with increasing age without a patient necessarily having CKD. There are also a number of drugs that cause a rise in plasma creatinine levels due to reduced tubular secretion (e.g. cimetidine, trimethoprim); this will result in a false reduction in calculated GFR.

There are a number of formulae available to calculate estimated GFR (eGFR); the MDRD (Modification of Diet in Renal Disease) was developed in 1999 and previously widely used, however more recent guidance suggests the use of the CKD-EPI equation (Chronic Kidney Disease Epidemiology Collaboration), the first version of which was developed in 2009. The main four variables used in both original equations are serum creatinine, age, sex, and race. The CKD-EPI equation is less biased, especially at higher GFRs, and its latest iteration (2021) does not include race.