Urea

Urea

• is a nitrogen-containing compound formed in the liver as the end product of protein metabolism and the urea cycle
• the vast majority (about 85%) of urea is eliminated through the kidneys, whereas the remainder is excreted through the gastrointestinal (GI) tract
• the levels of serum urea levels increase in conditions where renal clearance decreases, such as acute and chronic renal failure or impairment
  • raised urea levels have been identified as a risk factor for kidney disease progression in patients with moderate to severe CKD, independent of eGFR (1)
  • other possible causes of increased serum urea include:
    • upper gastrointestinal bleeding
    • dehydration
    • catabolic states
    • high protein diets
• causes of low serum levels incude (2):
  • starvation
  • low-protein diet
  • severe liver disease

Reference:

1. Seki M et al. Blood urea nitrogen is independently associated with renal outcomes in Japanese patients with stage 3-5 chronic kidney disease: a prospective observational study. BMC Nephrol. 2019 Apr 2;20(1):115.
2. Gounden V, Bhatt H, Jialal I. Renal Function Tests. [Updated 2024 Jul 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-.