Is a serum creatinine of 1.37 mg/dL concerning?

Is a Serum Creatinine of 1.37 mg/dL Concerning?

A creatinine of 1.37 mg/dL warrants concern and requires immediate calculation of estimated GFR (eGFR) to determine if this represents early chronic kidney disease, as this level approaches the threshold defining renal insufficiency (≥1.5 mg/dL in men or ≥1.3 mg/dL in women corresponding to eGFR <60 mL/min/1.73 m²). 1, 2

Clinical Significance

• This level represents Grade 1 renal dysfunction (1.5-2.0× above baseline if baseline was normal) and may indicate early CKD, particularly in women where the threshold is ≥1.3 mg/dL. 2

• The National Kidney Foundation emphasizes that serum creatinine alone is inadequate for assessing kidney function because it is affected by muscle mass, age, sex, race, and dietary factors beyond actual GFR. 1

• In elderly patients, this creatinine level is particularly concerning because serum creatinine underestimates renal dysfunction due to reduced muscle mass, meaning actual kidney function may be significantly worse than the number suggests. 2, 3

Immediate Assessment Required

Calculate eGFR using the MDRD or Cockcroft-Gault equation immediately rather than relying on creatinine alone, as these equations account for age, sex, race, and body size. 1, 2

Key Evaluation Steps:

• Determine if this is acute versus chronic: Check if creatinine increased ≥0.3 mg/dL within 48 hours or ≥50% from baseline, which would define acute kidney injury (AKI). 1, 4

• Assess for reversible causes: Evaluate volume status, recent contrast exposure, nephrotoxic medications, urinary obstruction, and infection. 2

• Check for albuminuria/proteinuria: This provides critical additional prognostic information and helps classify CKD severity. 1, 2

Clinical Context Matters

Patient-Specific Factors:

• In women: A creatinine of 1.37 mg/dL exceeds the 1.3 mg/dL threshold that corresponds to eGFR <60 mL/min/1.73 m², definitively indicating CKD Stage 3 or higher. 1

• In elderly patients: This level likely represents more severe renal impairment than apparent due to sarcopenia and reduced creatinine generation. 2, 3

• In patients with diabetes or hypertension: This level requires aggressive blood pressure control (<130/80 mmHg) and consideration of ACE inhibitors or ARBs if albuminuria is present. 4

• In patients on immune checkpoint inhibitors: This warrants closer monitoring for immune-related nephritis. 2

• In cirrhotic patients: Consider developing hepatorenal syndrome if accompanied by other clinical signs. 2

Management Algorithm

Step 1: Calculate eGFR and Establish Trend

• Repeat creatinine within 1-2 weeks to establish whether this is stable, improving, or worsening. 2
• Use prediction equations (MDRD or Cockcroft-Gault) to determine actual kidney function. 1

Step 2: Risk Stratification

• If eGFR <60 mL/min/1.73 m²: This confirms CKD Stage 3 or higher. 4
• If eGFR <45 mL/min/1.73 m²: Nephrology referral is indicated. 4
• If creatinine continues rising or exceeds 2.0 mg/dL: Urgent nephrology consultation required. 2

Step 3: Initiate Protective Measures

• Avoid nephrotoxic medications when possible (NSAIDs, aminoglycosides, contrast agents). 2
• Adjust medication dosing for renally cleared drugs based on eGFR, not creatinine alone. 1
• Target blood pressure <140/90 mmHg (or <130/80 mmHg if proteinuria or diabetes present). 2, 4

Step 4: Monitor Appropriately

• Check both eGFR and urine albumin-to-creatinine ratio (UACR) annually at minimum in patients with confirmed CKD. 4
• More frequent monitoring (every 3-6 months) if progressive decline or high-risk features present. 4

Critical Pitfalls to Avoid

• Do not dismiss this as "normal" without calculating eGFR, especially in elderly patients, women, or those with low muscle mass where creatinine significantly underestimates renal dysfunction. 1, 3

• Do not use 24-hour urine collections for creatinine clearance, as they are less accurate than eGFR equations and prone to collection errors. 1

• Do not discontinue ACE inhibitors/ARBs for creatinine increases <30% unless volume depletion is present, as these medications provide long-term renal protection. 4

• Do not assume stable creatinine means stable kidney function in critically ill or hospitalized patients, as reduced muscle mass and creatinine generation can mask declining GFR. 5