Does testosterone replacement therapy affect glomerular filtration rate (GFR) in men?

Impact of Testosterone Replacement Therapy on Glomerular Filtration Rate in Men

Testosterone replacement therapy (TRT) in men appears to improve glomerular filtration rate (GFR) in hypogonadal men, with studies showing increases in GFR over long-term treatment.

Effects of Testosterone on Renal Function

Direct Effects on GFR

• Long-term testosterone therapy has been shown to improve renal function parameters in hypogonadal men, with studies demonstrating:
  • Increase in GFR from baseline 87.0 ± 12.9 to 98.0 ± 8.0 mL/min/1.73 m² over 8 years of treatment 1
  • Decrease in serum urea and uric acid levels 1
  • Improved renal parameters compared to untreated hypogonadal controls who showed deterioration in GFR over time

Mechanism of Action

• Testosterone therapy may improve renal function through:
  • Changes in body composition (increased lean muscle mass)
  • Potential vasodilatory effects on renal vasculature
  • Reduction in inflammatory markers that may affect kidney function

Monitoring Considerations

Impact on Creatinine-Based GFR Estimation

• Testosterone replacement increases muscle mass, which can affect creatinine-based GFR calculations:
  • Increased muscle mass leads to higher creatinine production
  • This may result in falsely lower estimated GFR when using creatinine-based equations 2
  • After 1 year of testosterone therapy, men show approximately 4 kg increase in lean body mass 2

Alternative GFR Assessment

• For more accurate assessment of renal function in men on TRT:
  • Consider cystatin C-based GFR estimation, which is less dependent on muscle mass 2
  • If cystatin C is unavailable, interpret creatinine values in the context of testosterone therapy 2
  • Consider calculating GFR using both pre-TRT and current parameters to establish a range 3

Clinical Implications

Monitoring Recommendations

• Before initiating testosterone therapy:

  • Baseline assessment of renal function
  • Consider patient's existing renal status, especially in those with CKD

• During testosterone therapy:

  • Regular monitoring of renal function at 3-6 month intervals 2
  • Watch for unexplained decreases in eGFR, which may warrant discontinuation of therapy 2
  • Monitor for fluid retention, which is uncommon but can occur 2

Special Considerations

• In patients with existing renal disease:
  • TRT should be used cautiously in men with congestive heart failure or renal insufficiency due to potential fluid retention 2
  • No dose adjustment appears necessary for patients with end-stage renal disease on hemodialysis 4
  • Higher testosterone levels have been associated with lower mortality in men with CKD stages 3-4 5

Practical Application

1. Establish baseline renal function before starting TRT
2. Monitor renal function regularly during treatment
3. Consider cystatin C-based GFR estimation for more accurate assessment
4. Be aware that changes in creatinine may reflect changes in muscle mass rather than actual kidney function
5. Discontinue TRT if there is an unexplained decrease in eGFR

The evidence suggests that properly administered testosterone replacement therapy not only does not harm renal function but may actually improve GFR in hypogonadal men when monitored appropriately.