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Urea in Serum

Waste product of protein metabolism reflecting kidney clearance. Influenced by hydration, protein intake and tissue breakdown; synthesized in the liver.
Roche Method Sheet
Also known as:
Serum UreaS-urea.
Do not confuse with blood urea nitrogen (BUN), which reports nitrogen rather than whole urea. The two can be calculated from one another.

Urea ranges

Interpret your result
"Normal" lab range for Urea is between 2.76 and 8.07 mmol/L:
2.76
8.07
According to OptimalDX, Urea should be between 3.57 and 5.71 mmol/L:
3.57
5.71
Optimal range
Optimal range for Urea appears to be between 3.7 and 6.5 mmol/L:
1
3
3.7
6.5
8.5
16
Why this optimal range?
Preliminary range is based on functional health organizations including but not limited to those listed above.

What a low value may mean:

Common reasons for low Urea:

  • Protein intake and nutrition: Low protein intake, malnutrition or impaired absorption can reduce urea production.

    Dilution and pregnancy: Excess fluid intake or water retention can lower the concentration. Pregnancy commonly lowers urea through increased kidney filtration and plasma volume expansion.

    Less common: Advanced liver disease can impair urea synthesis.

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What a high value may mean:

Common reasons for high Urea:

  • Hydration and diet: Dehydration and high protein intake can raise urea even when kidney function is preserved.

    Reduced clearance: Kidney disease or reduced blood flow to the kidneys, including heart failure, can raise urea. Interpret alongside creatinine and eGFR.

    Increased protein breakdown: Fever, infection and corticosteroid use can increase urea production.

    Less common: Gastrointestinal bleeding adds a protein load from digested blood; urinary tract obstruction reduces excretion.

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Images:

Mortality was lowest near 5–6 mmol/L urea and rose at both low and high levels

Mortality was lowest near 5–6 mmol/L urea and rose at both low and high levels

Figure 4, UK Biobank panel. Axis labels corrected: the paper labels urea as BUN and the log hazard ratio as hazard ratio. Added table: adjusted HRs vs. the median (Table 2). Observational association.
425,264 participants
UK general-population adults aged 40-69 years
Dataset: UK Biobank
Prospective population-based cohort study
Urea rose with age in both sexes and was higher in men than in women

Urea rose with age in both sexes and was higher in men than in women

Supplementary Figure 3, urea panel (12,725 plotted). Lines are moving medians; bands are the central 95% in a 10-year age window. Sex color key added. Cross-sectional trend.
13,396 participants
Healthy adult volunteers aged 18-80 years from 12 countries
Dataset: IFCC global multicenter study on reference values
Cross-sectional multicenter study
Blood urea more than doubled as protein intake rose from 0.5 to 2.5 g/kg

Blood urea more than doubled as protein intake rose from 0.5 to 2.5 g/kg

Figure 2. Mean and ±2 SD band from 288 measurements taken throughout the day on days 5-6 of each diet. The original axis is whole urea in mg/dL; the mmol/L axis was added.
10 participants
Healthy medical students on weighed diets
Controlled-feeding experiment with three protein levels

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Zsolt Szabo
Zsolt Szabo
Precision Health Consultant for Longevity Clinics

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