What should I order for a workup of suspected pseudo Acute Kidney Injury (AKI) in the context of heavy resistance training and dehydration?

Workup for Suspected Pseudo-AKI from Resistance Training and Dehydration

In the context of heavy resistance training and dehydration, order serial serum creatinine measurements, urinalysis with microscopy, urine sodium and fractional excretion of sodium (FENa), and renal ultrasound to differentiate true AKI from transient creatinine elevation due to increased muscle breakdown and prerenal physiology.

Initial Laboratory Assessment

Essential First-Line Tests

• Serial serum creatinine measurements are critical to establish the trajectory and determine if this meets KDIGO AKI criteria (≥0.3 mg/dL increase within 48 hours or ≥1.5 times baseline within 7 days) 1
• Urinalysis with microscopic examination should be performed to detect hematuria, proteinuria, or abnormal urinary sediment that would indicate structural kidney disease rather than functional/prerenal causes 1
• Urine output monitoring if the patient is in a clinical setting, as oliguria (<0.5 mL/kg/h for 6 hours) is part of AKI staging 1

Urine Biochemistry for Differentiation

• Urine sodium concentration and fractional excretion of sodium (FENa) help distinguish prerenal from intrinsic renal injury 2, 3
  • FENa <1% with urine sodium <10 mEq/L strongly suggests prerenal physiology (dehydration) 2
  • FENa >1% suggests tubular injury or acute tubular necrosis 2, 3
  • Important caveat: These values can be confounded by recent diuretic use 1

Imaging Studies

• Renal ultrasound should be performed to assess kidney size and exclude obstruction 1, 2
  • Normal-sized kidneys support acute rather than chronic kidney disease 2
  • This is particularly important to rule out postrenal causes, though less likely in this clinical scenario 3

Key Diagnostic Considerations in This Context

Understanding Creatinine Elevation from Exercise

• Serum creatinine is affected by muscle injury and increased creatinine release from heavy resistance training, which can falsely suggest AKI 1
• Dehydration causes concentration effects on serum creatinine, potentially meeting AKI criteria without true kidney injury 1
• The combination of these factors creates "pseudo-AKI" where creatinine rises but kidney function may be preserved

Expected Findings in Pseudo-AKI

• Bland or normal urine sediment without casts, cells, or significant proteinuria 1, 2
• Low FENa (<1%) and low urine sodium (<10 mEq/L) consistent with appropriate renal sodium retention from dehydration 2
• Normal kidney size on ultrasound without hydronephrosis 2
• Improvement with hydration: In true prerenal physiology, volume replacement should reduce serum creatinine to within 0.3 mg/dL of baseline 1

Management Approach

• Discontinue nephrotoxic agents including NSAIDs commonly used by athletes 1, 4
• Provide volume resuscitation with isotonic fluids and reassess creatinine in 24-48 hours 1, 3
• Monitor for rhabdomyolysis: Check creatine kinase (CK) and urine myoglobin if there's concern for severe muscle breakdown, as this can cause true AKI 3

Critical Pitfall to Avoid

Do not assume all creatinine elevation in athletes is benign. While pseudo-AKI from exercise and dehydration is common, true AKI from rhabdomyolysis can occur with extreme resistance training and requires aggressive hydration 3. The presence of dark urine, markedly elevated CK (>5,000-10,000 U/L), or failure to improve with hydration should prompt consideration of true kidney injury requiring more intensive management.

Follow-Up Recommendations

• Repeat creatinine measurement at 3 months after any AKI episode to assess for resolution or development of chronic kidney disease, as recommended by KDIGO guidelines 1
• Even transient AKI increases long-term risk for kidney disease 1