TRT And Kidney Function: What Creatinine Readings Mean

Testosterone replacement therapy (TRT) can raise serum creatinine levels, but the increase typically reflects gains in lean body mass rather than kidney damage. Creatinine is a byproduct of muscle metabolism. Because TRT increases muscle tissue, more creatinine enters the bloodstream as a normal physiological response. The distinction matters because creatinine-based kidney function estimates may flag a false decline in men whose kidneys are working normally.

For men receiving care from a telehealth provider like Marek Health, understanding TRT and kidney function prevents unnecessary alarm and keeps lab interpretation accurate. The standard lab marker for kidney filtration, estimated glomerular filtration rate (eGFR), relies on creatinine. When muscle mass rises on TRT, eGFR calculations can suggest impaired filtration that may not reflect actual kidney function.

TRT and kidney function are linked through creatinine, a waste product of muscle metabolism that the kidneys filter from blood. Testosterone therapy increases muscle mass, which raises creatinine production without impairing kidney filtration. Cystatin C, a muscle-independent marker, provides a more accurate kidney function assessment for men on TRT.

A 2024 retrospective study of 227 competitive and recreational athletes with testosterone-induced muscle hypertrophy found that cystatin C showed no meaningful relationship with body composition (R² = 0.0001 in normal-BMI subjects), unlike creatinine, supporting the view that creatinine alone overstates kidney risk during TRT (Ashouri et al., 2024).

What Is Creatinine and How Does It Relate to Kidney Health?

Creatinine is produced at a roughly constant rate by skeletal muscle as it breaks down creatine phosphate for energy. Healthy kidneys filter creatinine out of the blood and excrete it in urine. When kidney function declines, creatinine accumulates in the bloodstream.

The normal serum creatinine range for adult men falls between 0.74 and 1.35 mg/dL, though lab reference ranges vary slightly. Doctors use creatinine to calculate eGFR, which estimates how well the kidneys filter waste. An eGFR above 90 mL/min/1.73m2 is considered normal. Below 60 suggests chronic kidney disease (CKD).

The problem with creatinine as a standalone marker is its dependence on muscle mass. A man who gains 10 pounds of lean tissue on TRT will produce more creatinine without any change in kidney performance. His eGFR will appear lower on paper, potentially triggering an unnecessary referral or medication adjustment.

How Testosterone Therapy Affects Creatinine Levels

TRT is thought to raise creatinine through two primary mechanisms, both tied to body composition rather than renal pathology.

First, testosterone is an anabolic hormone that promotes muscle protein synthesis. As lean body mass increases, creatine turnover accelerates and more creatinine enters circulation. This is an expected effect of testosterone's anabolic activity, which Endocrine Society guidelines acknowledge (Bhasin et al., 2018).

Second, TRT shifts body composition by reducing fat mass while adding muscle. This altered ratio changes baseline creatinine production relative to body weight, affecting eGFR calculations that were calibrated for average population body composition. Men on TRT who also supplement with creatine or do resistance training may show creatinine values at or above the upper reference range without any kidney involvement.

An 8-year observational study of 496 hypogonadal men found that treatment with testosterone undecanoate (312 men) was associated with higher GFR values over time, with the treated group's GFR rising from 87 to 98 mL/min/1.73m2. The untreated control group (184 men) saw GFR decline from 92 to 87 over the same period. The treated group was younger on average (59 vs. 66 years, p<0.0001), which limits causal interpretation (Alwani et al., 2021).

Does Elevated Creatinine on TRT Mean Kidney Damage?

Often, no. But distinguishing a muscle-mass artifact from true kidney impairment requires clinical evaluation.

Why eGFR Can Be Misleading During TRT

eGFR formulas (CKD-EPI being the current standard) use serum creatinine alongside age and sex to estimate kidney function. These formulas assume relatively stable muscle mass. TRT breaks that assumption.

A man whose creatinine rises from 1.0 to 1.2 mg/dL after six months on TRT may see his eGFR drop from 92 to 78, placing him in the "mildly decreased" category on paper while his kidneys filter normally. In many cases, this reflects a mathematical artifact rather than a disease process, but a provider should confirm that interpretation with additional testing.

Cystatin C as an Alternative Marker

Cystatin C is a small protein produced by all nucleated cells and is generally independent of muscle mass, though factors like thyroid function, obesity, and corticosteroid use can influence levels. Cystatin C-based eGFR calculations give a more accurate picture of kidney function in men with high or changing muscle mass.

The Ashouri et al. (2024) study found that in competitive and recreational athletes with testosterone-induced muscle hypertrophy, cystatin C bore no meaningful relationship to body composition, while creatinine did. These findings supported the view that creatinine alone may overstate kidney risk in men with high or changing muscle mass. Cystatin C-based eGFR is increasingly recognized as the preferred measure in populations where muscle mass distorts creatinine readings.

For men on TRT who show a creatinine increase, requesting a cystatin C measurement alongside standard labs provides a clearer answer about actual kidney status.

TRAVERSE Trial Findings on Kidney Function

The TRAVERSE trial enrolled 5,246 men aged 45-80 with diagnosed hypogonadism and cardiovascular risk factors. Its primary finding was that testosterone therapy was noninferior to placebo for major adverse cardiovascular events, with rates of 7.0% versus 7.3% (Lincoff et al., 2023).

On kidney outcomes, the trial reported a higher incidence of acute kidney injury (AKI) in the testosterone group (2.3%) compared to placebo (1.5%, p=0.04). The investigators noted this finding was "not expected." The testosterone group also showed higher rates of atrial fibrillation (3.5% vs. 2.4%) and pulmonary embolism (0.9% vs. 0.5%).

The absolute AKI rate was low, the definition of AKI in trial reporting captures a broad range of severity, and the study population carried substantial baseline cardiovascular risk. Still, the finding reinforces the importance of monitoring kidney markers throughout TRT.

Following TRAVERSE, the FDA issued class-wide labeling changes for testosterone products in February 2025, removing the prior boxed cardiovascular warning and adding a new blood pressure warning based on ambulatory blood pressure monitoring data (FDA, 2025). The limitation of use for age-related testosterone decline was retained.

How Should Kidney Function Be Monitored on TRT?

Providers typically include serum creatinine and eGFR in the baseline workup before starting TRT, and may also order cystatin C to establish a muscle-independent reference point. The AUA recommends diagnosing testosterone deficiency based on a total testosterone consistently below 300 ng/dL on two separate early-morning draws, alongside clinical symptoms (Mulhall et al., 2018). Kidney function markers should be part of that initial workup.

During treatment, providers typically recheck renal markers at 3-6 month intervals during the first year, then annually if values remain stable. If creatinine rises, the next step is assessing whether body composition has changed and whether cystatin C supports the creatinine finding.

A comparison of the two markers clarifies the clinical picture:

If both creatinine and cystatin C rise together, that warrants further evaluation for actual kidney impairment, including urinalysis for proteinuria and electrolyte assessment.

TRT in Men with Existing Kidney Disease

Testosterone deficiency is common in men with chronic kidney disease. The Alwani et al. (2021) registry study found that long-term testosterone therapy in hypogonadal men was associated with improved renal filtration markers compared to untreated controls, with a lower observed mortality rate in the treated group (7.8% vs. 15.2%, p=0.035). The groups differed at baseline in age (59 vs. 66 years) and other factors, and the study's authors noted that randomized controlled trials are still needed to confirm these findings. Other observational data suggest testosterone may delay progression to end-stage kidney disease in certain subgroups, though randomized evidence remains limited.

For men with CKD who have confirmed low testosterone, treatment decisions require a careful provider evaluation weighing potential benefits (improved anemia, muscle mass, quality of life) against risks (fluid retention, hematocrit elevation, blood pressure changes). Conservative dosing, closer lab intervals, and coordination between prescribers and nephrologists are standard practice in this population.

TRT doesn't correct kidney disease. It addresses a diagnosed hormonal deficiency that often coexists with renal impairment.

Common Misinterpretations and What to Watch For

The most frequent misinterpretation is treating a creatinine increase on TRT as evidence of kidney damage without checking cystatin C or accounting for muscle gains. Without context, this can sometimes prompt referrals or medication adjustments that a provider may reconsider after reviewing cystatin C and body composition data, or even premature discontinuation of therapy.

Other factors that can independently raise creatinine in men on TRT include creatine supplementation, high-protein diets, intense resistance training, and dehydration. These should be ruled out before attributing a creatinine increase to kidney dysfunction.

Men who use non-prescribed anabolic steroids face a different risk profile. Supraphysiologic doses of androgens have been associated with more substantial kidney stress than therapeutic TRT, including cases of focal segmental glomerulosclerosis reported in the literature. This is distinct from medically supervised replacement therapy at physiologic doses.

Red flags that do warrant urgent kidney evaluation include a rapid creatinine rise (more than 0.3 mg/dL within 48 hours), new proteinuria, declining urine output, or concurrent signs of fluid overload. These findings point to a process beyond the expected muscle-mass effect and require prompt clinical assessment. The bottom line on TRT and kidney function: read creatinine in context, not in isolation.

Disclaimer: This blog post is intended for informational purposes only and should not be considered medical advice. Always consult a healthcare professional before making changes to your health routine.

FAQs

Does TRT directly damage the kidneys?

Current evidence doesn't suggest TRT directly damages healthy kidneys. The creatinine increase seen with testosterone therapy is typically a byproduct of increased muscle mass, not kidney injury. The TRAVERSE trial did report a small, unexplained increase in acute kidney injury events, but absolute rates were low (2.3% vs. 1.5%), and the study population carried substantial cardiovascular risk factors. Individual risk factors should be discussed with a provider.

What creatinine level should concern men on TRT?

A mild creatinine increase (0.1-0.2 mg/dL) in the first months of TRT is expected and usually reflects muscle growth. A rise above 1.3-1.4 mg/dL, a rapid jump of more than 0.3 mg/dL within 48 hours, or a persistent upward trend warrants further evaluation with cystatin C testing and a full review of kidney markers.

Should men on TRT request cystatin C testing?

Cystatin C provides a muscle-independent assessment of kidney function and is a valuable addition to standard labs for men on TRT. It's useful when creatinine-based eGFR drops but there's no other evidence of kidney impairment. Providers can order cystatin C alongside routine bloodwork.

Can creatine supplements and TRT together harm the kidneys?

Creatine supplementation raises serum creatinine levels by increasing the body's creatine pool, which naturally converts to creatinine. Combined with TRT-related muscle gains, this can produce creatinine readings that look concerning but don't reflect kidney damage. Men using both should inform their provider so lab results are interpreted correctly.

How often should kidney function be tested during TRT?

Most clinical protocols include kidney markers at baseline, then at 3-6 month intervals during the first year of treatment. After that, annual monitoring is typical if values stay stable. Men with pre-existing kidney conditions may need more frequent testing based on their provider's evaluation.

Does stopping TRT lower creatinine levels?

Discontinuing TRT generally leads to a decrease in muscle mass over time, which reduces creatinine production and lowers serum levels. This pattern confirms the creatinine elevation was muscle-driven rather than kidney-related. Any TRT discontinuation should be managed under provider supervision to address hormonal recovery and symptom management.

References

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• Ann Med Surg (Lond). 2021;69:102748.

• J Clin Endocrinol Metab. 2018;103(5):1715-1744.

• J Urol. 2018;200(2):423-432.

• N Engl J Med. 2023;389(2):107-118.

• U.S. Food and Drug Administration. Drug Alerts and Statements. Feb 2025.