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Serum Creatinine with Direct Measurement of Blood Urea Nitrogen (BUN) Ratio

Published: August 9, 2026Updated: August 16, 2026

This test measures your blood levels of creatinine and urea nitrogen (BUN) to help assess kidney function and fluid balance.

Quick summary

["A ratio helps doctors check kidney health and identify potential issues with fluid retention or kidney damage."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
94554-3
Short code
sCD14-ST SerPlBld IA-mCnc
Synonyms
sCD14-ST SerPlBld IA-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ia
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What This Test Measures

Creatinine is a waste product from muscle metabolism that kidneys filter out. BUN reflects how well your kidneys process urea, a waste product from protein breakdown. Together, they provide insight into kidney function and overall fluid balance in your body.

Why It Matters in Kidney Health

Kidneys play a vital role in filtering waste from your blood. Elevated creatinine or BUN levels may signal reduced kidney function, while abnormal ratios can indicate conditions like dehydration, heart failure, or kidney disease.

When You Might Need This Test

Your doctor may order this test if you have symptoms like swelling, fatigue, or changes in urine output. It’s also used before surgeries, during pregnancy, or to monitor chronic conditions like diabetes or high blood pressure.

Common Conditions Monitored

This test helps diagnose or track kidney disease, dehydration, heart failure, or conditions affecting fluid balance, such as liver disease or severe infections.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Creatinine:BUN Ratio (Serum)

Frequently asked questions

Why do doctors check my creatinine and BUN levels together?
Checking both together helps provide a clearer picture of kidney function and fluid balance. While creatinine alone can indicate kidney damage, BUN levels can reflect hydration status and other metabolic factors. A ratio can help identify specific issues, such as dehydration or heart-related fluid retention.
What do my test results mean if they’re high or low?
High levels of either creatinine or BUN may suggest kidney problems, dehydration, or other health conditions. Low levels might indicate overhydration or certain liver issues. Your doctor will interpret results in the context of your overall health and symptoms.
Can diet or medications affect these test results?
Yes, diet (especially protein intake) and medications (like certain diuretics or NSAIDs) can influence BUN levels. Creatinine levels are less affected by diet but may change with muscle mass or kidney function. Always discuss your medications and diet with your doctor before or after testing.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy