Uraemia

The concentration of urea or creatinine in blood or plasma represents the dynamic equilibrium between production and elimination. In healthy subjects there is an enormous reserve of renal excretory function, and serum urea and creatinine do not rise above the normal range until there is a reduction of 50-60% in the GFR.

Thereafter, the level of urea depends both on the GFR and the production rate. The latter is heavily influenced by protein intake and tissue catabolism. The level of creatinine is much less dependent on diet but is more related to age, sex and muscle mass.

Once it is elevated, serum creatinine is a better guide to GFR than urea and, in general, measurement of serum creatinine is a good way to monitor further deterioration in the GFR.

A diagnosis of uraemia requires two components: azotaemia and symptoms and signs of uraemia.