Kidney Function Tests (KFTs)
Author- Dr. Mohammad Shamim, MD
Overview
Kidney function tests are a group of tests that evaluate how well the kidneys are working. These tests are crucial in diagnosing and managing conditions related to kidney health.
The primary kidney function tests include
Blood Urea Nitrogen (BUN):
- What it measures: The amount of urea nitrogen in the blood. Urea is a waste product formed in the liver and carried to the kidneys for excretion.
- Significance: High levels may indicate kidney dysfunction, dehydration, or high protein intake. Low levels could indicate liver disease or malnutrition.
Serum Creatinine:
- What it measures: The level of creatinine, a waste product from muscle metabolism, in the blood.
- Significance: Elevated levels can indicate impaired kidney function or kidney disease, as creatinine is normally filtered out by healthy kidneys.
Glomerular Filtration Rate (GFR):
- What it measures: An estimate of how much blood passes through the glomeruli (tiny filters in the kidneys) each minute.
- Significance: A low GFR indicates reduced kidney function. It is used to stage chronic kidney disease (CKD).
Urinalysis:
- What it measures: Various components in the urine, including proteins, glucose, ketones, blood, and signs of infection.
- Significance: Abnormal results can indicate kidney disease, urinary tract infections, or other metabolic conditions.
Urine Albumin-to-Creatinine Ratio (UACR):
- What it measures: The amount of albumin (a type of protein) in the urine compared to the amount of creatinine.
- Significance: Elevated levels of albumin in the urine can be an early sign of kidney damage.
Electrolytes and Blood Chemistry:
- What it measures: Levels of electrolytes (such as sodium, potassium, calcium) and other chemicals in the blood.
- Significance: Imbalances can indicate kidney dysfunction, as the kidneys regulate electrolyte levels in the blood.
Normal Value of Each Parameters of Kidney Function Tests
Blood Urea Nitrogen (BUN):
- Normal Range: 7-20 mg/dL (2.5-7.1 mmol/L)
- Significance: Values higher than normal can indicate kidney dysfunction, dehydration, or high protein intake.
Serum Creatinine:
- Normal Range:
- Men: 0.74-1.35 mg/dL (65-115 µmol/L)
- Women: 0.59-1.04 mg/dL (52-92 µmol/L)
- Significance: Elevated levels may indicate impaired kidney function.
Glomerular Filtration Rate (GFR):
- Normal Range: 90-120 mL/min/1.73 m²
- Significance: A GFR below 60 mL/min/1.73 m² for three months or more is a sign of chronic kidney disease (CKD).
Urinalysis:
- Normal Values:
- Protein: Negative
- Glucose: Negative
- Ketones: Negative
- Blood: Negative
- Significance: Presence of these substances can indicate kidney disease, diabetes, or infections.
Urine Albumin-to-Creatinine Ratio (UACR):
- Normal Range: Less than 30 mg/g (3.4 mg/mmol)
- Significance: Higher levels can be an early sign of kidney damage.
Electrolytes and Blood Chemistry:
- Normal Ranges:
- Sodium (Na+): 135-145 mEq/L (135-145 mmol/L)
- Potassium (K+): 3.5-5.0 mEq/L (3.5-5.0 mmol/L)
- Calcium (Ca2+): 8.5-10.2 mg/dL (2.12-2.55 mmol/L)
- Bicarbonate (HCO3-): 22-28 mEq/L (22-28 mmol/L)
Significance of Kidney Function Tests
- Early Detection: These tests help in early detection of kidney disease, which is crucial for timely intervention and management.
- Monitoring Chronic Conditions: They are essential for monitoring chronic kidney disease (CKD) and adjusting treatments accordingly.
- Assessing Treatment Efficacy: They help evaluate the effectiveness of treatments for kidney-related conditions.
- Overall, Health Assessment: As kidneys play a vital role in maintaining overall health by filtering waste and balancing fluids, electrolytes, and other substances, these tests provide insight into general well-being.
Conclusion
Regular kidney function tests are important for individuals with risk factors such as diabetes, hypertension, a family history of kidney disease, or other conditions that affect kidney health.
References
- Current Medical Diagnosis and Treatment
- Harrison’s Principle of Internal Medicine