Kidney Function Test (KFT)

 

Kidney Function Test (KFT)

 


Introduction

A Kidney Function Test (KFT), also known as a Renal Function Test (RFT), is a group of blood and urine tests used to evaluate how well the kidneys are functioning. The kidneys are essential organs that filter waste products, excess water, and toxins from the blood while maintaining electrolyte balance, acid-base balance, and blood pressure.

KFT helps diagnose kidney diseases, monitor chronic kidney disease (CKD), detect acute kidney injury (AKI), evaluate electrolyte disorders, and assess the effectiveness of treatment.

Definition

Kidney Function Test (KFT) is a panel of laboratory tests that measures waste products, electrolytes, proteins, and filtration capacity to evaluate kidney function, diagnose renal diseases, and monitor treatment.

Objectives of KFT

The major objectives of Kidney Function Tests are:

  • Assess kidney function.
  • Detect acute kidney injury (AKI).
  • Diagnose chronic kidney disease (CKD).
  • Evaluate electrolyte imbalance.
  • Monitor patients with diabetes and hypertension.
  • Detect dehydration.
  • Monitor patients receiving dialysis.
  • Assess response to treatment.
  • Evaluate kidney function before surgery.
  • Screen individuals at risk of kidney disease.

Principle of the Test

Healthy kidneys continuously filter blood through millions of nephrons. During this process:

  • Waste products such as urea and creatinine are removed.
  • Electrolytes such as sodium, potassium, and chloride are regulated.
  • Water balance and acid-base balance are maintained.

When kidney function decreases, these substances accumulate in the blood or become abnormal. KFT measures these biochemical markers using automated laboratory analyzers.

Sample Required

Blood Sample

  • Venous blood
  • Serum or plasma

Urine Sample

  • Random urine sample
  • 24-hour urine collection (if required)

Patient Preparation

  • Fasting is generally not required, unless requested by the laboratory.
  • Drink adequate water before testing.
  • Avoid excessive meat intake before the test.
  • Inform the healthcare provider about any medications or supplements.
  • Follow instructions carefully for a 24-hour urine collection, if prescribed.

Procedure

  1. Collect 3–5 mL of venous blood.
  2. Separate serum by centrifugation.
  3. Measure kidney function markers using an automated biochemistry analyzer.
  4. Collect a urine sample if urine tests are requested.
  5. Interpret results together with the patient's medical history and symptoms.

Components of Kidney Function Test

1. Serum Creatinine

Function

Creatinine is a waste product produced from normal muscle metabolism. Healthy kidneys remove creatinine from the blood.

Normal Range

  • Male: 0.7–1.3 mg/dL
  • Female: 0.6–1.1 mg/dL

Increased in

  • Acute kidney injury
  • Chronic kidney disease
  • Kidney obstruction
  • Severe dehydration

Clinical Significance

Serum creatinine is one of the most reliable indicators of kidney function.

2. Blood Urea Nitrogen (BUN)

Function

Urea is produced in the liver during protein metabolism and is excreted by the kidneys.

Normal Range

7–20 mg/dL

Increased in

  • Kidney failure
  • Dehydration
  • High-protein diet
  • Gastrointestinal bleeding

Decreased in

  • Severe liver disease
  • Malnutrition

Clinical Significance

Elevated BUN suggests reduced kidney function or increased protein breakdown.

3. Serum Urea

Normal Range

15–40 mg/dL

Increased in

  • Kidney disease
  • Dehydration
  • High protein intake

Decreased in

  • Liver disease
  • Malnutrition

4. Estimated Glomerular Filtration Rate (eGFR)

Function

eGFR estimates how efficiently the kidneys filter blood.

Normal Range

≥90 mL/min/1.73 m²

Interpretation

eGFR

Kidney Function

≥90

Normal

60–89

Mild decrease

30–59

Moderate CKD

15–29

Severe CKD

<15

Kidney failure

Clinical Significance

eGFR is one of the best overall indicators of kidney function.

5. Uric Acid

Function

Uric acid is formed from the breakdown of purines.

Normal Range

  • Male: 3.5–7.2 mg/dL
  • Female: 2.6–6.0 mg/dL

Increased in

  • Gout
  • Kidney disease
  • Leukemia
  • High purine diet

6. Sodium (Na⁺)

Normal Range

135–145 mmol/L

Increased in

  • Dehydration
  • Diabetes insipidus

Decreased in

  • Kidney disease
  • Heart failure
  • SIADH

7. Potassium (K⁺)

Normal Range

3.5–5.0 mmol/L

Increased in

  • Kidney failure
  • Acidosis
  • Tissue injury

Decreased in

  • Vomiting
  • Diarrhea
  • Diuretic therapy

8. Chloride (Cl⁻)

Normal Range

98–106 mmol/L

Increased in

  • Dehydration
  • Metabolic acidosis

Decreased in

  • Vomiting
  • Metabolic alkalosis

9. Bicarbonate (HCO₃⁻)

Normal Range

22–28 mmol/L

Decreased in

  • Metabolic acidosis
  • Kidney failure

Increased in

  • Metabolic alkalosis

10. Calcium

Normal Range

8.5–10.5 mg/dL

Abnormal in

  • Chronic kidney disease
  • Parathyroid disorders
  • Vitamin D deficiency

11. Phosphate (Phosphorus)

Normal Range

2.5–4.5 mg/dL

Increased in

  • Kidney failure
  • Hypoparathyroidism

Decreased in

  • Hyperparathyroidism
  • Vitamin D deficiency

Urine Tests Included in KFT

  • Urine protein
  • Urine albumin
  • Urine creatinine
  • Albumin-to-creatinine ratio (ACR)
  • Routine urinalysis
  • 24-hour urine protein (when indicated)

Interpretation of KFT Results

Test Result

Possible Condition

High Creatinine

Kidney dysfunction

High BUN/Urea

Kidney disease, dehydration

Low eGFR

Chronic kidney disease

High Potassium

Kidney failure

Protein in Urine

Kidney damage

High Uric Acid

Gout, kidney disease

Diseases Diagnosed by KFT

  • Acute Kidney Injury (AKI)
  • Chronic Kidney Disease (CKD)
  • Glomerulonephritis
  • Nephrotic syndrome
  • Kidney stones
  • Diabetic nephropathy
  • Hypertensive nephropathy
  • Urinary tract obstruction
  • Polycystic kidney disease
  • Electrolyte disorders
  • Dehydration

Advantages

  • Simple blood and urine tests
  • Early detection of kidney disease
  • Monitors kidney function over time
  • Detects electrolyte imbalance
  • Helps guide treatment decisions
  • Widely available and cost-effective
  • Useful for routine health screening

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Limitations

  • Abnormal values do not always indicate permanent kidney disease.
  • Results may be affected by dehydration, diet, medications, or muscle mass.
  • Some kidney disorders require additional investigations such as ultrasound, CT scan, MRI, or kidney biopsy.
  • eGFR estimates may be less accurate in pregnancy, children, or people with very high or very low muscle mass.

Precautions

  • Drink adequate water unless instructed otherwise.
  • Inform the healthcare provider about all medications and supplements.
  • Avoid strenuous exercise before testing.
  • Follow instructions carefully for urine sample collection.
  • Ensure proper handling of blood and urine specimens.

Clinical Significance

Kidney Function Tests are essential for evaluating renal health, detecting kidney disease at an early stage, monitoring disease progression, and assessing the effectiveness of treatment. They are routinely used in patients with diabetes, hypertension, cardiovascular disease, and other conditions that may affect kidney function.

Conclusion

The Kidney Function Test (KFT) is a comprehensive panel of blood and urine tests used to assess kidney health and filtration efficiency. It includes measurements of serum creatinine, blood urea nitrogen (BUN), urea, eGFR, uric acid, electrolytes, calcium, phosphate, and urine proteins. KFT plays a vital role in the early diagnosis of kidney diseases, monitoring chronic kidney disorders, evaluating electrolyte balance, and guiding treatment decisions. Due to its accuracy, simplicity, and clinical importance, KFT is one of the most commonly performed laboratory investigations in modern medicine.

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