Urea - plasma or serum

5 mL blood in lithium heparin or plain tube.

Neonate: 1.0-4.0 mmol/L
Adult: 3.0-8.0 mmol/L

Increased levels are seen with reduced glomerular filtration due to renal or pre-renal disease; bleeding into the gastrointestinal tract; hypercatabolic states.

Reduced values are seen in pregnancy; with water retention; with reduced synthesis as a result of decreased protein intake, severe liver disease, or urea-cycle defects.