Kidney Function Test (KFT/RFT) | Normal Range, Cost & Procedure

What is Kidney Function Test?

KFT full form - Kidney Function Test

A kidney function test (KFT) is a group of blood and urine tests used to evaluate how well the kidneys are working in filtering waste products, maintaining fluid balance, and regulating essential electrolytes in the human body. These combined tests primarily measure substances such as serum creatinine, blood urea nitrogen (BUN), and estimated glomerular filtration rate (eGFR), along with urine markers like albumin (a protein), which help detect early kidney damage and monitor ongoing kidney conditions. These tests provide quantitative measures of kidney performance and are essential for diagnosing, staging, and monitoring kidney diseases, including chronic kidney disease (CKD) and acute kidney injury (AKI).

Kidney Function Test Procedure

Kidney Function Test Preparation Before the Procedure

• Consultation with the Doctor: The individual should discuss with the Nephrologists for any medications, health conditions, or allergies that might affect the results of kidney function tests, especially medications like diuretics, ACE inhibitors, or NSAIDs. 
• Fasting Requirements: Although fasting is generally not required for kidney function tests. However, if additional tests like blood sugar or cholesterol levels are being conducted along with kidney function tests, 8-12 hours of fasting may be necessary and need to be followed as advised by the doctor. 
• Hydration: Individuals should be advised to drink plenty of water before the test, unless directed otherwise by the doctor, as dehydration can affect the results of certain tests (e.g., creatinine and eGFR). 
• Avoid Exercise and Proteinaceous Diet: It is recommended to avoid heavy exercises and a high-protein diet for 24 hours before the kidney function test. This is because through intense physical exercise and high protein intake it might temporarily raise creatinine levels, potentially leading to incorrect test findings.
• Clothing: A short-sleeved or sleeveless shirt is recommended, as blood is typically drawn from the arm.
  
  

During the Kidney Function Test

Blood Test:

• A phlebotomist (trained healthcare professional) will clean the area (usually the inner elbow) and use a sterile needle to draw 5–10 ml of blood. The sample is then sent to the laboratory for analysis, including tests for serum creatinine, BUN, and eGFR. 
• A tourniquet (it is a surgical device, such as a strip of cloth or a band of rubber, that is wrapped tightly around a leg or an arm to prevent the flow of blood to the leg or the arm) is applied to make veins more visible, ensuring easier blood collection. After the test, the individual may feel slight discomfort or a small bruise at the puncture site.
  
  

Urine Test:

• A spot urine sample may be collected to check for protein or albumin levels. 
• A 24-hour urine collection may be required for more detailed analysis of creatinine clearance and urinary protein levels.
  
  

After the Kidney Function Test

• Post-Blood Test Care: After the blood sample is collected, the individual will be asked to apply pressure to the site to stop bleeding. The arm may need to remain slightly bent for a few minutes. 
• Post-Urine Test: If a 24-hour urine collection is required for a case, it's important to ensure all urine collected over 24 hours is returned to the laboratory in the provided container. The collection bottle may contain preservatives like thymol, so avoid direct contact with skin and mucous membranes. Keep the bottle out of reach of small children to prevent accidental ingestion of the preservatives to avoid any mishappening. 
• Complications: While rare, mild bruising, soreness, or fatigue may occur at the blood draw site. If severe pain, prolonged bleeding, or swelling happens, the individual should consult the doctor.

Kidney Function Test Normal Range Chart – Normal Values

The following chart provides the normal reference ranges for key kidney function tests. These values help assess kidney health and are essential for diagnosing and monitoring kidney-related conditions along with abnormal values may indicate potential kidney diseases or systemic conditions.

Important Notes:

• Gender variation: Serum creatinine and creatinine clearance are generally higher in males due to greater muscle mass. 
• Age factor: 
• eGFR declines gradually with advancing age, even it can happen in healthy individuals 
• Elderly individuals may have normal creatinine but reduced kidney function due to lower muscle mass 
• Interpretation should always consider age-adjusted kidney function 
• Laboratory variation: Normal ranges may vary slightly depending on the laboratory methods and reference standards
  

Interpreting Kidney Function Tests

Kidney function tests (KFT) are interpreted by analysing a combination of blood tests for kidney function and urine tests for kidney function, with the parameters that reflect the kidney’s ability to filter waste, regulate electrolytes, and maintain fluid balance. All of these tests are critical for detecting kidney issues, tracking disease development, and evaluating therapy efficacy. No single test is sufficient; a panel-based interpretation is required for accurate clinical assessment.

The interpretation of key parameters is as follows:

• Serum Creatinine
• Blood Urea Nitrogen (BUN)
• Estimated Glomerular Filtration Rate (eGFR)
• Urine Albumin / Protein (UACR)
• Electrolytes (Sodium, Potassium, Bicarbonate)
• Creatinine Clearance / 24-Hour Urine Test for Kidney Function
• Uric Acid
  
  

Serum Creatinine: It is one of the primary indicators and key marker of kidney filtration.

• Normal values of Serum Creatinine: 
• For Male: 0.7 to 1.3 mg/dL 
• For Female: 0.6 to 1.1 mg/dL 
• Mild increase: It can be seen in early kidney dysfunction or dehydration 
• Significant increase: This suggests acute kidney injury (AKI) or chronic kidney disease (CKD) 
• Serum creatinine ≥2 mg/dL generally indicates moderate to severe kidney dysfunction 

Creatinine levels are muscle mass-dependent, so values can be lower in older adults and women.

Blood Urea Nitrogen (BUN): This reflects nitrogen waste in the blood and should always be interpreted along with creatinine.

• Normal BUN: 7 to 20 mg/dL 
• Elevated BUN: It indicates possible kidney dysfunction, dehydration, or increased protein breakdown. 
• High BUN with high creatinine: This suggests intrinsic kidney disease or acute kidney injury (AKI). 
• High BUN with normal creatinine: May suggest dehydration, gastrointestinal bleeding, or high-protein intake.
  
  

Estimated Glomerular Filtration Rate (eGFR): It is the most reliable and accurate indicator of overall kidney function and is used to stage kidney disease.

• Normal eGFR: ≥90 mL/min/1.73 m²: It indicates healthy kidney filtration. 
• Mild reduction (60–89 mL/min/1.73 m²): This may be normal with age or without other abnormalities.
• Moderate reduction (30–59 mL/min/1.73 m²): This indicates moderate kidney damage (CKD stage 3). 
• Severe reduction (15–29 mL/min/1.73 m²): It indicates severe kidney dysfunction (CKD stage 4). 
• Kidney failure (<15 mL/min/1.73 m²): This indicates kidney failure (CKD stage 5), requiring dialysis or transplant. 

eGFR declines naturally with age, and lower values can be normal in elderly individuals with no kidney disease.

Urine Albumin / Protein or Urine Albumin-to-Creatinine Ratio (UACR): It reflects kidney damage, especially when it occurs with glomerular injury.

• Normal values: 
• <30 mg/g creatinine (normal). 
• Moderate increase (30–300 mg/g): Early kidney damage (microalbuminuria). 
• Severe increase (>300 mg/g): Significant kidney disease (macroalbuminuria). 

Persistent albuminuria is a key early marker of kidney damage or renal problem, particularly in diabetes and hypertension.

Electrolytes Balance (Sodium, Potassium, Bicarbonate): Kidneys maintain electrolyte balance and regulate acid–base status.

• Serum sodium normal value (135 to 145 mEq/L). 
• Abnormal values suggest fluid imbalance or renal dysfunction 
• Serum potassium normal value (3.5 to 5.0 mEq/L). 
• High potassium (hyperkalemia) indicates impaired renal potassium excretion and can be life-threatening problem. 
• Serum bicarbonate normal value (22 to 28 mEq/L). 
• Low bicarbonate suggests metabolic acidosis, commonly noticed in kidney dysfunction.
  
  

Creatinine Clearance / 24-Hour Urine Test for Kidney Function: Creatinine clearance provides a direct estimate of kidney filtration and is often used when eGFR is inconclusive.

• Normal values of creatinine clearance (90 to 140 mL/min): Indicates healthy kidney function.
• For Male: 97 to 137 mL/min. 
• For Female: 88 to 128 mL/min. 
• Reduced clearance: Indicates impaired kidney function. 
• This test is useful when eGFR values are borderline or less accurate.
• The 24-hour urine test is a diagnostic tool used to assess kidney function by measuring substances (sodium, potassium, and urea) that are filtered by the kidneys over a full 24-hour period.
  
  

Uric Acid: It is a by-product of purine metabolism, filtered by the kidneys. High levels of uric acid can cause gout and kidney stones.

• Normal Range of Uric acid (3.5 to 7.2 mg/dL): 
• For Male: 3.5 to 7.2 mg/dL.
• For Female: 2.6 to 6.0 mg/dL. 
• Elevated uric acid levels: May indicate gout, kidney stones, or kidney dysfunction. 
• Very high levels can lead to uric acid crystal formation in joints (gout) or kidneys (stones).
• Low Uric Acid may sometimes be seen in chronic kidney disease or Wilson’s disease.
• Males tend to have higher uric acid levels due to differences in excretion patterns, while females generally have lower levels before menopause.
  

Factors That Could Interfere with Kidney Function Tests