eGFR and creatinine clearance in relation to metabolic changes in an unselected patient population

It is widely assumed that moderate to severe renal failure (creatinine clearance <60 ml/min; or an MDRD-4 (Modification of Diet in Renal Disease equation) <60 ml/min/1.73 m(2)) is associated with metabolic changes, often needing further assessment and treatment. We investigated whether such abnormalities are already present at earlier stages of kidney disease, as assessed by 24-hour urine sampling and MDRD-4 calculation.

A select, retrospective cohort study was conducted. Creatinine clearance was measured by collecting 24-hour urines. The individual eGFRs were calculated with the MDRD-4 formula and patients were then divided by renal function category (<15, 15-30, 30-45, 45-60, 60-90, >90 ml/min(/1.73 m(2))). Per clearance category the number of people with anaemia, hypokalaemia, uraemia and hyperphosphataemia was evaluated.

The median creatinine clearance rate was 67.3 ml/min (quartiles: 42.9-95.8) versus a median MDRD-4-eGFR of 51.6 ml/min/1.73 m(2) (35.8-67.7). Anaemia, hyperkalaemia, hypocalcaemia, and uraemia were found to be present at higher levels of creatinine clearance rate and eGFR than previously reported (p<0.0005). This increased prevalence was more pronounced in elderly subjects, particularly with respect to anaemia (OR 2.71 and 2.02 for MDRD-4 and creatinine clearance respectively, p<0.0005). The same holds for the proportion with uraemia (OR 1.85, p<0.0005) and hypocalcaemia (OR 1.97, p=0.011) for MDRD-4.

Metabolic changes in an in- and outpatient hospital population are present at earlier stages than was stated in recent guidelines, especially when creatinine clearance levels are used as indicators. This might have implications for testing and treatment of patients with suspected kidney disease and/or loss of renal function.