table of contents
- Read more : HOMA-IR and Insulin Resistance: Understanding the Key to Metabolic Health
- 1. Blood Tests for Kidney Function
- A. Serum Creatinine (Cr)
- B. Blood Urea Nitrogen (BUN)
- C. Estimated Glomerular Filtration Rate (eGFR)
- D. Cystatin C
- 2. Urine Tests for Kidney Function
- A. Urinalysis
- B. Urine Albumin-to-Creatinine Ratio (UACR)
- C. 24-Hour Urine Collection
- 3. Electrolyte & Acid-Base Balance Tests
- A. Serum Potassium (K⁺)
- B. Serum Sodium (Na⁺)
- C. Serum Bicarbonate (HCO₃⁻)
- 4. Advanced Kidney Function Tests
- Conclusion
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| Take care of your kidneys |
Kidney function tests (KFTs) are essential diagnostic tools used to assess renal health, detect kidney disease, and monitor treatment efficacy. The kidneys play a vital role in filtering waste, balancing electrolytes, and maintaining fluid homeostasis. This article provides an in-depth overview of key kidney function tests, their normal ranges, clinical significance, and interpretation.
1. Blood Tests for Kidney Function
A. Serum Creatinine (Cr)
- Normal Range:
- Men: 0.7 - 1.3 mg/dL
- Women: 0.6 - 1.1 mg/dL
- Children: 0.2 - 1.0 mg/dL
- Clinical Significance:
- Elevated levels indicate reduced kidney function, dehydration, or muscle breakdown.
- Decreased levels may suggest muscle wasting or malnutrition.
B. Blood Urea Nitrogen (BUN)
- Normal Range: 7 - 20 mg/dL
- Clinical Significance:
- Increased levels suggest kidney dysfunction, dehydration, or high protein intake.
- Decreased levels may be seen in liver disease or malnutrition.
C. Estimated Glomerular Filtration Rate (eGFR)
- Normal: > 90 mL/min/1.73m²
- Chronic Kidney Disease (CKD) Staging:
- Stage 1: eGFR ≥ 90 (Normal function with kidney damage)
- Stage 2: 60-89 (Mild decrease)
- Stage 3: 30-59 (Moderate decrease)
- Stage 4: 15-29 (Severe decrease)
- Stage 5: <15 (Kidney failure)
- Clinical Significance:
- A lower eGFR indicates declining kidney function and progression of CKD.
D. Cystatin C
- More sensitive than creatinine for early detection of kidney dysfunction.
- Less affected by muscle mass, making it useful in elderly or malnourished patients.
2. Urine Tests for Kidney Function
A. Urinalysis
- Examines urine for protein, blood, glucose, and casts.
- Proteinuria (Protein in urine): Indicates kidney damage (e.g., nephrotic syndrome).
- Hematuria (Blood in urine): May indicate infection, kidney stones, or glomerulonephritis.
B. Urine Albumin-to-Creatinine Ratio (UACR)
- Normal: < 30 mg/g
- Microalbuminuria (30-300 mg/g): Suggests early kidney disease.
- Macroalbuminuria (>300 mg/g): Indicates significant kidney damage.
C. 24-Hour Urine Collection
- Measures creatinine clearance and protein excretion.
- Used for precise kidney function assessment.
3. Electrolyte & Acid-Base Balance Tests
A. Serum Potassium (K⁺)
- Normal: 3.5 - 5.0 mEq/L
- Elevated: Suggests kidney failure, acidosis.
- Low: Seen in excessive diuretic use or vomiting.
B. Serum Sodium (Na⁺)
- Normal: 135 - 145 mEq/L
- Elevated: May indicate dehydration, diabetes insipidus.
- Low: Common in kidney failure, SIADH.
C. Serum Bicarbonate (HCO₃⁻)
- Normal: 22 - 28 mEq/L
- Decreased levels: Indicate metabolic acidosis, often seen in CKD.
4. Advanced Kidney Function Tests
- Renal Imaging: Ultrasound, CT scan to assess kidney structure.
- Renal Biopsy: Used for diagnosing glomerulonephritis and unexplained kidney disease.
- Fractional Excretion of Sodium (FENa): Differentiates pre-renal and intrinsic kidney diseases.
Conclusion
Regular kidney function tests are essential for early detection of kidney disease, especially in high-risk individuals such as those with diabetes, hypertension, and cardiovascular disease. Early intervention can slow disease progression and improve outcomes. If abnormalities are detected, further testing and consultation with a nephrologist are recommended.