Is a normal alanine aminotransferase (ALT), normal aspartate aminotransferase (AST), normal blood urea nitrogen (BUN), low serum creatinine with a high estimated glomerular filtration rate (eGFR), and otherwise normal comprehensive metabolic panel appropriate for a 70‑year‑old woman?

Assessment of Laboratory Values in a 70-Year-Old Female

Direct Answer

These laboratory values are NOT entirely appropriate and require immediate clinical correlation—the reported eGFR of 150 mL/min/1.73 m² is physiologically implausible for a 70-year-old woman and indicates either a laboratory error or misinterpretation of low serum creatinine. 1

Critical Issue: The Paradox of Low Creatinine and High eGFR

The fundamental problem is that low serum creatinine in elderly patients reflects reduced muscle mass, not enhanced kidney function. 2 A creatinine that appears "normal" can mask significant renal impairment in older adults because creatinine production decreases with age-related sarcopenia independently of actual kidney function. 1

Why This Matters Clinically

• In elderly patients, serum creatinine does not reflect age-related decline in GFR because concomitant muscle mass loss reduces creatinine generation. 2
• A serum creatinine of 1.2 mg/dL can represent a creatinine clearance of 110 mL/min in a young adult but only 40 mL/min in an elderly patient. 3, 4
• Among elderly patients with normal serum creatinine measurements, one in five had asymptomatic renal insufficiency when assessed by creatinine clearance methods. 3, 4

Immediate Action Required

Calculate actual creatinine clearance using the Cockcroft-Gault formula immediately—do not rely on the reported eGFR. 3, 4 The Cockcroft-Gault equation is:

CrCl (mL/min) = [(140 - age) × weight (kg)] / [72 × serum creatinine (mg/dL)] × 0.85 (for females) 2, 4

What the True Renal Function Likely Shows

• Without knowing the patient's weight, precise calculation is impossible, but for a typical 70-year-old woman weighing approximately 60 kg with a low creatinine, the actual creatinine clearance is likely in the 50-70 mL/min range (Stage 2-3A CKD), not 150 mL/min. 3, 4
• The Cockcroft-Gault formula systematically underestimates GFR in elderly patients, meaning even calculated values may overestimate true renal function. 2, 4

Interpretation of Other Laboratory Values

Liver Enzymes (ALT 30, AST 28)

These values are appropriate and within normal range for a 70-year-old woman. 5, 6 However, recognize that:

• AST and ALT levels decrease proportionally as GFR declines in chronic kidney disease. 7
• Reference values for 70-year-old women show ALT and AST typically remain within standard adult ranges (upper limit ~40 U/L). 5

BUN and BUN/Creatinine Ratio

• BUN 14 mg/dL is within normal limits (acceptable up to 28-35 mg/dL in elderly). 8
• BUN/creatinine ratio of 32 is elevated (normal 10-20), which paradoxically suggests either prerenal azotemia, dehydration, or high protein catabolism—this finding contradicts the implausibly high eGFR and supports the need for clinical reassessment. 1

Clinical Algorithm for Management

Step 1: Verify Laboratory Accuracy

• Confirm the serum creatinine value and ensure proper laboratory calibration to IDMS standards. 2
• Check if the laboratory used Jaffe method (overestimates creatinine by 5-15%) versus enzymatic assay. 4

Step 2: Calculate True Renal Function

• Obtain patient's current weight and height. 4
• Apply Cockcroft-Gault formula for medication dosing decisions. 3, 4
• Consider cystatin C-based eGFR if creatinine-based estimates remain unreliable due to extreme body composition. 1, 4

Step 3: Assess Hydration Status

• The elevated BUN/creatinine ratio suggests possible dehydration, which can falsely elevate creatinine and reduce GFR. 3
• Dehydration is a common pitfall that can mask true renal function in elderly patients. 3

Step 4: Medication Safety Review

• Review all current medications within 48 hours to identify nephrotoxic agents (NSAIDs, diuretics, ACE inhibitors, ARBs). 3
• Adjust doses of renally-cleared medications according to Cockcroft-Gault-derived creatinine clearance, not the reported eGFR. 3, 4
• Drug manufacturers established renal dosing guidelines using Cockcroft-Gault, not MDRD or CKD-EPI equations. 3, 4

Step 5: Follow-Up Monitoring

• Repeat creatinine and calculated CrCl in 3 months to establish trajectory of kidney function. 3
• Perform annual urinalysis with urine albumin-to-creatinine ratio to assess proteinuria and CKD progression risk. 3
• Monitor blood pressure targeting <130/80 mmHg for nephroprotection. 3

Common Pitfalls to Avoid

• Never use serum creatinine alone to assess kidney function in elderly patients—this is an explicit Level A recommendation from the National Kidney Foundation. 2
• Do not use eGFR (MDRD or CKD-EPI) for medication dosing—these equations are designed for CKD diagnosis and staging, not drug dosing. 3, 4
• Do not assume low creatinine equals excellent kidney function—it almost always reflects low muscle mass in elderly patients. 1, 4
• Do not overlook hydration status—dehydration can falsely alter both creatinine and GFR estimates. 3

Bottom Line

The reported eGFR of 150 mL/min/1.73 m² is a red flag requiring immediate verification and recalculation using Cockcroft-Gault with actual body weight. 3, 1, 4 The true creatinine clearance is likely 50-70 mL/min (Stage 2-3A CKD), necessitating medication dose adjustments and nephroprotective strategies. 3, 4 The elevated BUN/creatinine ratio further supports the need for clinical reassessment of volume status and true renal function. 1