Urea

A product of the urea cycle resulting from ammonia breakdown, it depends upon adequate liver function for its synthesis and adequate renal function for its excretion. Low levels are thus seen in cirrhosis and high levels in renal failure. Uraemia is a clinical syndrome including lethargy, drowsiness, confusion, pruritus and pericarditis resulting from high plasma levels of urea (or, more correctly, nitrogenous waste products — azotaemia).

The ratio of urine:plasma urea may be useful in distinguishing oliguria of renal or pre-renal origins. Higher ratios (>10:1) are seen in pre-renal conditions, e.g. hypovolaemia, whereas low levels (<4:1) occur with direct renal causes.

24-h measurement of urinary urea (or nitrogen) excretion has been previously used as a guide to nutritional protein replacement but is currently not considered a useful routine tool.

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