How can I assess kidney disease based on my bloodwork results, including serum creatinine levels, Blood Urea Nitrogen (BUN), electrolyte levels, and Glomerular Filtration Rate (GFR)?

Assessing Kidney Disease Through Bloodwork Parameters

To assess kidney disease, you should get bloodwork that includes serum creatinine with eGFR calculation, urinary albumin-to-creatinine ratio (ACR), blood urea nitrogen (BUN), and electrolytes. 1

Key Laboratory Tests for Kidney Disease Assessment

Primary Tests

• Estimated Glomerular Filtration Rate (eGFR)

  • Most important measure of kidney function 1
  • Calculated from serum creatinine using validated equations (CKD-EPI preferred over MDRD) 1
  • Normal or increased: ≥90 ml/min/1.73 m² (G1)
  • Mildly reduced: 60-89 ml/min/1.73 m² (G2)
  • Moderately reduced: 45-59 ml/min/1.73 m² (G3a) and 30-44 ml/min/1.73 m² (G3b)
  • Severely reduced: 15-29 ml/min/1.73 m² (G4)
  • Kidney failure: <15 ml/min/1.73 m² (G5) 1

• Urinary Albumin-to-Creatinine Ratio (ACR)

  • Key marker of kidney damage 1
  • Categories:
    • A1 (normal to mildly increased): <30 mg/g
    • A2 (moderately increased): 30-300 mg/g
    • A3 (severely increased): >300 mg/g 1
  • Single spot urine sample is sufficient; timed collections usually unnecessary 1

Supporting Tests

• Blood Urea Nitrogen (BUN)

  • Less specific than creatinine but provides complementary information 2
  • BUN/creatinine ratio can help identify pre-renal causes of kidney dysfunction 3
  • Normal range varies by laboratory 2

• Electrolytes

  • Sodium, potassium, chloride, bicarbonate
  • Abnormalities may indicate kidney dysfunction 1
  • Particularly important in advanced CKD (stages G4-G5) 1

Interpreting Results and CKD Classification

CKD Definition

• CKD is defined as abnormalities of kidney structure or function present for >3 months with implications for health 1
• Requires EITHER:
  • GFR <60 ml/min/1.73 m² for ≥3 months
  • OR markers of kidney damage (such as albuminuria) for ≥3 months 1

Risk Stratification

• Low risk: G1A1, G2A1 (green category)
• Moderately high risk: G1A2, G2A2, G3aA1 (yellow category)
• High risk: G1A3, G2A3, G3aA2, G3bA1 (orange category)
• Very high risk: G3aA3, G3bA2-A3, G4A1-A3, G5A1-A3 (red category) 1

Important Considerations

Limitations of Single Measurements

• Single abnormal values of eGFR or ACR should not be used to diagnose CKD 1
• Confirm abnormal results with repeat testing over at least 3 months 1
• Consider potential causes of transient changes (acute kidney injury, dehydration, medications) 1

Enhanced Assessment

• Cystatin C-based eGFR (eGFRcys) should be considered when:

  • Creatinine-based eGFR is 45-59 ml/min/1.73 m² without albuminuria
  • Confirmation of CKD is needed
  • Creatinine-based estimates may be inaccurate (extremes of muscle mass, diet, etc.) 1, 4

• Combined creatinine-cystatin C equation (eGFRcr-cys):

  • More accurate than either marker alone 4
  • Particularly useful for confirming CKD diagnosis in borderline cases 1, 4

Common Pitfalls to Avoid

• Relying solely on serum creatinine without calculating eGFR 1

  • Serum creatinine alone is inadequate for assessing kidney function
  • Normal creatinine can exist despite significant GFR reduction, especially in elderly or those with low muscle mass 1

• Ignoring albuminuria when eGFR is normal 1

  • Albuminuria is an independent risk factor for CKD progression and cardiovascular outcomes
  • Normal eGFR with albuminuria still indicates kidney damage 1

• Misinterpreting BUN values without context 2, 5

  • BUN is affected by many non-renal factors (protein intake, catabolism, dehydration)
  • Should be interpreted alongside creatinine, not in isolation 2, 5

• Using outdated terminology like "microalbuminuria" 1

  • Current guidelines recommend using specific ACR categories instead 1

By systematically evaluating these laboratory parameters and understanding their interpretation within the CKD classification framework, you can effectively assess your kidney function status.