The effect of gender-affirming hormone treatment on serum creatinine in transgender and gender-diverse youth: implications for estimating GFR

Background Equations for estimated glomerular filtration rate (eGFR) based on serum creatinine include terms for sex/gender. For transgender and gender-diverse (TGD) youth, gender-affirming hormone (GAH) treatment may affect serum creatinine and in turn eGFR. Methods TGD youth were recruited for this prospective, longitudinal, observational study prior to starting GAH treatment. Data collected as part of routine clinical care were abstracted from the medical record. Results For participants designated male at birth (DMAB, N = 92), serum creatinine decreased within 6 months of estradiol treatment (mean +/- SD 0.83 +/- 0.12 mg/dL to 0.76 +/- 0.12 mg/dL, p < 0.001); for participants designated female at birth (DFAB, n = 194), serum creatinine increased within 6 months of testosterone treatment (0.68 +/- 0.10 mg/dL to 0.79 +/- 0.11 mg/dL, p < 0.001). Participants DFAB treated with testosterone had serum creatinine similar to that of participants DMAB at baseline, whereas even after estradiol treatment, serum creatinine in participants DMAB remained higher than that of participants DFAB at baseline. Compared to reference groups drawn from the National Health and Nutritional Examination Survey, serum creatinine after 12 months of GAH was more similar when compared by gender identity than by designated sex. Conclusion GAH treatment leads to changes in serum creatinine within 6 months of treatment. Clinicians should consider a patient's hormonal exposure when estimating kidney function via eGFR and use other methods to estimate GFR if eGFR based on serum creatinine is concerning.