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Serum Creatinine to Albumin Ratio (Creatinine-Albumin Ratio, CAR) or Albumin-Creatinine Ratio (ACR) – *qualitative* screening test

Published: August 9, 2026Updated: August 14, 2026

This test measures the ratio of creatinine (a waste product from muscle breakdown) to albumin (a protein in your blood) in your serum. It helps assess kidney function and protein loss in urine.

Quick summary

["A simple blood test to check kidney health and protein levels over time."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 14, 2026Editorial policy

Key facts at a glance

LOINC
44731-8
Short code
CDT-ASI-DSI
Synonyms
CDT Asialo/CDT Disialo SerPl
Category
chemistry
Sample
serum
Container
Serum separator tube (SST) or red-top tube; plasma may be collected in heparin or EDTA tube
Units
N/A
Ref low
0
Ref high
1
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
High-performance liquid chromatography (HPLC) or capillary electrophoresis; sometimes LC-MS/MS for confirmation
CPT
82975 (transferrin); some labs use 82542 or unlisted code for CDT fractionation
SNOMED
395142002
Specimen volume
1-2 mL of serum or plasma
Stability
Stable for 7 days at 2-8°C; for longer storage, freeze at -20°C or below for up to 3 months
Hemolysis max
50
Lipemia max
100
Icterus max
50
TAT
48–168 hours
Order
routine

What Does This Test Measure?

Creatinine is a byproduct of muscle metabolism that the kidneys filter out. Albumin is a protein that stays in the bloodstream. The ratio helps identify if your kidneys are working properly or if protein is leaking into urine, which can signal conditions like kidney disease or proteinuria.

Why Might You Need This Test?

Your doctor may order this test if you have symptoms like swelling, frequent urination, fatigue, or if you have a history of kidney problems, diabetes, or high blood pressure. It’s also used in certain screening protocols to monitor chronic conditions.

How Is the Test Performed?

A small blood sample is taken from a vein in your arm. The sample is sent to a lab where it’s analyzed to determine the creatinine and albumin levels, then the ratio is calculated. Results are qualitative (qualitative screening), meaning they indicate whether the ratio is within expected ranges or not.

What Are the Possible Results?

Since this is a qualitative screening test, results typically fall into broad categories: *Normal* (no significant kidney or protein loss), *Abnormal* (may indicate kidney issues or protein loss), or *Requires Further Testing* (if your doctor suspects a problem and wants more details). Exact numeric ranges aren’t provided here.

Reference range

Asialo/Disialo transferrin ratio typically <1.0 (or <0.05 depending on reporting method); consult laboratory-specific reference rangeN/A

Specimen: serum

No special preparation required; recent alcohol consumption within 2 weeks may affect results and should be documented

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

A high creatinine-to-albumin ratio may suggest kidney dysfunction, chronic kidney disease, or conditions like nephrotic syndrome (where large amounts of protein leak into urine). A low ratio might indicate dehydration or other metabolic issues. This test is often used as a preliminary check before more detailed kidney function tests.

Short name

CAR Screening

Frequently asked questions

What Does a Positive or Abnormal Result Mean?
An abnormal result doesn’t always mean you have a serious condition, but it may prompt further testing (like urine protein tests or kidney function panels). Your doctor will discuss next steps based on your symptoms and medical history.
How Often Should I Get This Test?
Your doctor will determine how often you need this test based on your health status. For example, people with diabetes or kidney disease may need it more frequently than others.
Can I Eat or Drink Anything Before the Test?
No special preparation is needed for this test. However, if your doctor has specific instructions (e.g., fasting), follow them to ensure accurate results.
  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 14, 2026. · Read our editorial policy