KFT assesses renal function by evaluating glomerular filtration, tubular function, and electrolyte balance. It is crucial in diagnosing acute kidney injury (AKI), chronic kidney disease (CKD), acid-base disorders, and electrolyte imbalances.
🔹 1. Core Parameters in KFT & Clinical Significance
| Test | Normal Range | Clinical Interpretation |
|---|---|---|
| Serum Creatinine (S.Cr) | 0.6 – 1.2 mg/dL | ↑: AKI, CKD, Rhabdomyolysis, Urinary Obstruction ↓: Low muscle mass, Liver disease |
| Blood Urea Nitrogen (BUN) | 7 – 20 mg/dL | ↑: AKI, CKD, GI Bleed, Dehydration, Heart Failure ↓: Liver disease, Malnutrition |
| BUN/Creatinine Ratio | 10:1 to 20:1 | >20:1: Pre-renal AKI <10:1: Intrinsic AKI (ATN, GN) |
| Glomerular Filtration Rate (GFR) | >90 mL/min/1.73m² | ↓: CKD, AKI ↑: Pregnancy, High-output heart failure |
| Serum Uric Acid | 3.5 – 7.2 mg/dL | ↑: CKD, Gout, Tumor Lysis Syndrome ↓: SIADH, Wilson’s Disease |
| Serum Sodium (Na⁺) | 135 – 145 mEq/L | ↑: Hypernatremia (Dehydration, Diabetes Insipidus) ↓: Hyponatremia (SIADH, CKD, CHF) |
| Serum Potassium (K⁺) | 3.5 – 5.0 mEq/L | ↑: AKI, CKD, Addison’s, Metabolic Acidosis ↓: Vomiting, RTA, Diuretics |
| Serum Chloride (Cl⁻) | 96 – 106 mEq/L | ↑: Hyperchloremic Acidosis ↓: Metabolic Alkalosis |
| Serum Bicarbonate (HCO₃⁻) | 22 – 28 mEq/L | ↓: Metabolic Acidosis ↑: Metabolic Alkalosis |
| Urine Protein (Proteinuria) | <150 mg/day | ↑: CKD, Glomerulonephritis, Diabetes |
| Urine Osmolality | 500 – 850 mOsm/kg | ↓: CKD, Diabetes Insipidus ↑: SIADH, Dehydration |
🔹 2. Interpretation of KFT in Kidney Diseases
A. Acute Kidney Injury (AKI)
📌 Definition: Sudden decrease in renal function over hours to days.
🔹 Diagnosis (KDIGO Criteria)
- ↑ Serum Creatinine by ≥0.3 mg/dL in 48 hrs OR >50% from baseline in 7 days
- Urine Output <0.5 mL/kg/hr for 6 hours
🔹 Types of AKI & Diagnostic Clues
| Parameter | Pre-Renal (Hypovolemia, CHF, Sepsis) | Intrinsic (ATN, Glomerulonephritis) | Post-Renal (Obstruction, BPH, Tumor) |
|---|---|---|---|
| BUN/Creatinine Ratio | >20:1 | 10-15:1 | Variable |
| Urine Sodium (UNa) | <20 mEq/L | >40 mEq/L | Variable |
| Fractional Excretion of Na⁺ (FENa%) | <1% | >2% | Variable |
| Urine Sediment | Bland | Muddy brown casts, RBC casts | Normal or Crystals |
🔹 Example Interpretation:
- BUN/Cr = 25:1, Urine Na <10 → Pre-Renal AKI (Dehydration, Heart Failure)
- BUN/Cr = 12:1, Urine Na >40 → Intrinsic AKI (ATN)
B. Chronic Kidney Disease (CKD)
📌 Definition: GFR <60 mL/min for >3 months OR Kidney Damage (Proteinuria, Abnormal Imaging)
🔹 Key Findings in CKD
- ↓ GFR (<90 mL/min)
- ↑ Creatinine & BUN
- Proteinuria (Albumin/Creatinine Ratio >30 mg/g)
- Electrolyte Imbalances (Hyperkalemia, Metabolic Acidosis)
🔹 CKD Staging (KDIGO Criteria)
| Stage | GFR (mL/min/1.73m²) | Clinical Features |
|---|---|---|
| Stage 1 | >90 | Early kidney damage (Proteinuria) |
| Stage 2 | 60 – 89 | Mild CKD |
| Stage 3a | 45 – 59 | Moderate CKD |
| Stage 3b | 30 – 44 | Moderate-severe CKD |
| Stage 4 | 15 – 29 | Severe CKD |
| Stage 5 (ESRD) | <15 | Dialysis required |
🔹 Example Interpretation:
- GFR = 40, Proteinuria = 500 mg/day → CKD Stage 3b
C. Electrolyte & Acid-Base Disturbances in Kidney Disease
| Disorder | Lab Findings | Common Causes |
|---|---|---|
| Hyponatremia (↓ Na⁺) | Na⁺ <135 | SIADH, CKD, CHF, Cirrhosis |
| Hypernatremia (↑ Na⁺) | Na⁺ >145 | Dehydration, DI |
| Hypokalemia (↓ K⁺) | K⁺ <3.5 | Diuretics, RTA, Vomiting |
| Hyperkalemia (↑ K⁺) | K⁺ >5.5 | AKI, CKD, Addison’s, Rhabdomyolysis |
| Metabolic Acidosis | HCO₃⁻ <22, pH <7.35 | AKI, CKD, DKA |
| Metabolic Alkalosis | HCO₃⁻ >28, pH >7.45 | Vomiting, Diuretics |
🔹 Example Interpretation:
- Na⁺ = 125, Serum Osmolality = 260 → SIADH
- K⁺ = 6.2, ECG = Peaked T waves → Hyperkalemia (urgent treatment needed)
🔹 3. Clinical Decision-Making Using KFT
🔹 If Creatinine is suddenly elevated?
→ Check Urine Na & BUN/Cr ratio to differentiate Pre-Renal vs. ATN
🔹 If CKD is diagnosed?
→ Monitor GFR, Proteinuria, Electrolytes regularly
🔹 If Potassium is >6.5?
→ Immediate intervention (Calcium Gluconate, Insulin, Dialysis)