Creatinine is a waste product produced by the muscles during the breakdown of a compound called creatine, which plays a key role in producing energy for muscle contractions. Creatinine is filtered out of the blood by the kidneys and excreted in urine.

Key Points:

Measurement in Blood and Urine: Creatinine levels are commonly measured to assess kidney function. High levels in the blood may indicate impaired kidney function or kidney disease, while low levels may be related to reduced muscle mass, pregnancy or severe liver disease.

Normal Ranges:

Blood Creatinine Levels:

Men: 0.74 to 1.35 mg/dL

Women: 0.59 to 1.04 mg/dL

Creatinine Clearance Test: This test measures how well the kidneys filter creatinine from the blood into urine, giving a more accurate picture of kidney function.

Factors Affecting Levels:

Increased Creatinine: This may be observed due to kidney damage, dehydration, certain medications, high muscle mass or intense exercise.

Decreased Creatinine: This may result from reduced muscle mass, aging, or certain liver diseases.

A kidney function test (KFT) is a group of tests used to evaluate how well the kidneys are working. These tests help diagnose conditions affecting the kidneys, monitor their function and guide treatment decisions.

Here are the main components of a kidney function test:

1. Serum Creatinine

Purpose: Measures the amount of creatinine in the blood, a waste product from muscle metabolism.

Normal Range:

Men: 0.74 to 1.35 mg/dL

Women: 0.59 to 1.04 mg/dL

Indication: Elevated levels suggest impaired kidney function or disease.

2. Blood Urea Nitrogen (BUN)

Purpose: Measures the amount of urea nitrogen, another waste product filtered by the kidneys.

Normal Range: 6 to 24 mg/dL

Indication: High levels indicate reduced kidney function, dehydration, or excessive protein breakdown.

3. Estimated Glomerular Filtration Rate (eGFR)

Purpose: Estimates how well the kidneys are filtering waste from the blood.

Normal Range:

90–120 mL/min/1.73 m²

Indication: Lower eGFR indicates reduced kidney function or chronic kidney disease (CKD). Below 60 mL/min for three months may suggest CKD.

4. Urinalysis

Purpose: Examines the physical, chemical, and microscopic properties of urine.

Normal Range: No protein, glucose, or blood should be present in urine.

Indication: Abnormalities, such as proteinuria or hematuria, can indicate kidney damage or infections.

5. Creatinine Clearance Test

Purpose: Measures how well creatinine is cleared from the blood through the kidneys, using both blood and urine samples.

Normal Range:

Men: 97 to 137 mL/min

Women: 88 to 128 mL/min

Indication: Low creatinine clearance suggests reduced kidney function.

6. Albumin-to-Creatinine Ratio (ACR)

Purpose: Measures the amount of albumin (a type of protein) in the urine relative to creatinine.

Normal Range: Less than 30 mg/g

Indication: Higher levels of albumin in urine indicate kidney damage (albuminuria), often seen in diabetic kidney disease.

7. Cystatin C Test (less common)

Purpose: Measures the level of cystatin C, a protein filtered by the kidneys.

Indication: Can be a more sensitive indicator of kidney function, particularly in early kidney disease.

When Are These Tests Needed?

Symptoms of kidney disease (fatigue, swelling, changes in urination)

Monitoring known kidney conditions, diabetes, or high blood pressure

Risk Factors like family history, age, or heart disease

Regular kidney function testing is essential for early detection and management of kidney-related issues.