Kidney function tests (KFTs) are among the most important tools to assess how well your kidneys are working and to evaluate your overall health. Let’s explore what these tests are and why they matter.


What Are Kidney Function Tests?

Kidney function tests are a group of blood and urine tests used to evaluate how efficiently your kidneys are performing their essential roles, including:

  • Filtering waste and excess fluids from the body
  • Balancing electrolytes and fluids
  • Regulating hormone and mineral levels


Regular testing can help detect kidney disease early and allow for more effective treatment. (1)


Why Are Kidney Function Tests Done?

Whether done routinely or as part of a diagnostic workup, these tests serve several essential purposes: (2)


1. Early Detection of Kidney Disease

Kidney damage often goes unnoticed until the disease is in an advanced stage. Kidney function tests help detect problems before symptoms appear, allowing for early intervention and better outcomes.


2. Monitoring Existing Kidney Conditions

If you have a diagnosed kidney condition, regular testing helps your doctor track the disease’s progression and tailor your treatment plan to avoid complications.


3. Risk Assessment

Certain factors like diabetes, high blood pressure, or a family history of kidney disease increase your risk. Kidney tests help identify early changes so you can take preventative steps.


4. Treatment Guidance

Some medications can affect kidney function. Testing ensures early detection of any side effects and allows your doctor to adjust your medication accordingly.


Common Kidney Function Tests

Kidney function tests include the following: (1)


1. Blood Tests


  • Serum Creatinine: A waste product normally filtered by the kidneys. Elevated levels may signal kidney dysfunction.
  • Blood Urea Nitrogen (BUN): A nitrogenous waste filtered by healthy kidneys. High BUN may indicate reduced kidney performance.
  • Electrolyte Levels: Including sodium (Na), potassium (K), chloride (Cl), and blood pH.
  • Minerals: Such as phosphorus, calcium, and uric acid.
  • eGFR (Estimated Glomerular Filtration Rate): Measures how much blood the kidneys filter per minute.



2. Urine Tests


  • Urinary albumin (protein) test
  • Routine urinalysis
  • Urine culture
  • 24-hour urine test to measure electrolytes such as calcium, oxalate, citrate, phosphate, uric acid, and creatinine — useful for diagnosing kidney stones
  • Hormone tests from 24-hour urine collection — especially for patients under 40 with high blood pressure


How Are Kidney Function Tests Performed?

Blood samples are collected and analyzed in a lab.

Urine tests may involve a single sample or a 24-hour urine collection in a special container. (2)


Do You Need to Prepare for the Test?

Most kidney function tests do not require fasting. However, your doctor might recommend other tests that do. Make sure to inform your doctor of any medications you're taking, as they may affect the results. (2)


Understanding Kidney Test Results

Your test report will include specific codes and values. You can interpret them using the table below: (3)

Kidney Test Code

Test Meaning

Normal Values

eGFR

Glomerular Filtration Rate

Ideal: >90

Acceptable: 60–90

Serum Creatinine / Creatinine

Blood Creatinine

5–20 mg/dL

BUN

Blood Urea Nitrogen

Males: 0.6–1.2 mg/dL

Females: 0.5–1.1 mg/dL

Albuminurea

Urine Albumin Test

Less than 30

Sodium (Na)

Sodium

135–145 mmol/L

Potassium (K)

Potassium

3.5–5 mmol/L

Phosphate (PO4)

Phosphate

0.9–1.3 mmol/L

Calcium (Ca)

Calcium

2.2–2.6 mmol/L

⚠️ Normal values may vary depending on age, gender, physical activity, medications, and lab equipment. Always consult your doctor to interpret your results accurately. (3)


References