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Test Code Billings Clinic: 4082 Urea Nitrogen (BUN)/Creatinine Ratio, Plasma or Serum

Important Note

Blood samples from some patients with monoclonal gammopathies may produce falsely elevated results.

Performing Laboratory

Billings Clinic Laboratory: Chemistry

Useful For

  • The BUN/Creatinine ratio is useful in the differential diagnosis of acute or chronic renal disease.
  • Reduced renal perfusion, e.g., congestive heart failure, or recent onset of urinary tract obstruction will result in an increase in BUN/Creatinine ratio.
  • Increased urea formation also results in an increase in the ratio, e.g., gastrointestinal bleeding, trauma, etc.
  • When there is decreased formation of urea as seen in liver disease, there is a decrease in the BUN/Creatinine ratio.
  • In most cases of chronic renal disease the ratio remains relatively normal.

Specimen Requirements

Submit only 1 of the following specimens:

Serum or plasma should be physically separated from cells as soon as possible with a maximum limit of two hours from the time of collection.

 

Plasma

  • Draw blood in a green-top (lithium heparin) tube(s).
  • Spin down and send 1.0 mL of heparinized plasma frozen.

 

Serum

  • Draw blood in a plain, red-top tube(s) or a serum gel tube(s).
  • Spin down and send 1.0 mL of serum frozen

Storage/Stability

Specimen Type Temperature Time
Serum, Plasma Refrigerated 7 days
  Frozen (preferred) 1 month
  Ambient 24 hours

Reject Due To

  • Hemolysis
  • Gross icterus

Reference Values

BUN/Creatinine Ratio:  7 - 29

 

See individual test listings for other reference values.

Day(s) Test Set Up

Daily

Test Classification and CPT Coding

82565 - creatinine

84520 - Urea nitrogen, quantitative

LOINC Code Information

Reporting Name LOINC Code
BUN 3094-0
Creatinine 2160-0
BUN/Creat Ratio 3097-3

 

Profile/Testing Information

Profile Information:
Creatinine

Urea Nitrogen (BUN)/Creatinine Ratio (Calculation)
Urea Nitrogen (BUN)  

 

Interferences

BUN

  • Hemoglobin at 250 mg/dL increases the UN result in serum/plasma at 9 mg/dL by 14%.
  • Conjugated bilirubin at 30 mg/dL decreases the UN result in serum/plasma at 40 mg/dL by -14%.

 

Creatinine

  • Unconjugated bilirubin at 15 mg/dL decreases the creatinine result in serum/plasma at 1.62 mg/dL by -13.4%.
  • Unconjugated bilirubin at 20 mg/dL decreases the creatinine result in serum/plasma at 5.32 mg/dL by -16.1%.
  • Glucose at 332 mg/dL increases the creatinine result in serum/plasma at 1.61 mg/dL by 10.6%.
  • Cefoxitin at 5.0 mg/dL increases the creatinine result in serum/plasma at 1.53 mg/dL by 17.0%.
  • Pyruvate at 10.0 mg/dL increases the creatinine result in serum/plasma at 1.53 mg/dL by 17.6%. Dopamine at 100 mg/dL increases the creatinine result in serum/plasma at 1.53 mg/dL by 13.7%.
  • Total Protein at 12.0 mg/dL increases the creatinine result in serum/plasma at 1.71 mg/dL by 10.5%.