Elevated Creatinine and eGFR - What is Your Stage of CKD

Making Sense of Creatinine and eGFR on Your Blood Work

If you have ever had routine blood work done, especially as part of a TRT or hormone optimization protocol, you have seen creatinine and eGFR values on your results. For most people, these numbers get a quick glance and then get forgotten. But if your creatinine comes back elevated or your eGFR is lower than expected, it can trigger anxiety and confusion, especially if your doctor mentions the possibility of chronic kidney disease. Dr. Shafiq Cheema walks through exactly what these values mean, how they are calculated, and what to do if yours are abnormal.

Creatinine is a waste product generated by normal muscle metabolism. Your muscles use creatine for energy, and creatinine is the byproduct of that process. It is continuously produced at a relatively constant rate and filtered out of the blood by your kidneys. Because the production rate is fairly stable and the kidneys are responsible for clearing it, blood creatinine levels serve as a rough proxy for how well your kidneys are filtering.

eGFR stands for estimated glomerular filtration rate. It is a calculated value, not a direct measurement. The formula takes your creatinine level and adjusts it based on age, sex, and sometimes race and body size to estimate how many milliliters of blood your kidneys are filtering per minute. A normal eGFR is above 90 mL/min. Values between 60 and 89 indicate mildly decreased function, and values below 60 sustained over three or more months meet the criteria for chronic kidney disease.

Why Creatinine Can Be Misleading in Active People

Here is where it gets important for anyone involved in fitness, bodybuilding, or hormone therapy. Creatinine production is directly related to muscle mass. The more muscle you carry, the more creatinine your body produces as a baseline. This means that a muscular 200-pound man will naturally have a higher creatinine level than a sedentary 150-pound man, even if both have perfectly healthy kidneys.

This creates a real problem with interpretation. The reference ranges on standard lab reports are based on population averages that include people of all body compositions. A creatinine of 1.3 mg/dL might be flagged as high on the lab report, but for a well-muscled man, it could be completely normal. The eGFR formula, which uses creatinine as its primary input, will also be skewed. A muscular man may have an eGFR that appears low not because his kidneys are impaired but because his creatinine is naturally elevated due to greater muscle mass.

Men on TRT face an additional confounding factor. Testosterone promotes muscle protein synthesis and increases lean body mass. As you gain muscle on TRT, your baseline creatinine production increases. This can cause a gradual rise in serum creatinine over time that has nothing to do with kidney function and everything to do with having more metabolically active muscle tissue.

Creatine supplementation adds yet another variable. If you take creatine monohydrate, which is one of the most well-studied and popular sports supplements, your creatinine levels will be elevated simply because you are providing your body with more of the precursor. This is a well-known confounder that even experienced clinicians sometimes overlook.

When to Actually Worry

While it is important not to panic over a mildly elevated creatinine in the context of high muscle mass or creatine use, it is equally important not to dismiss kidney concerns entirely. There are red flags that warrant further investigation regardless of your body composition. A rapid increase in creatinine over a short period (weeks rather than months) is more concerning than a slightly elevated but stable value. Creatinine above 1.5 mg/dL in someone without an obvious explanation like extreme muscle mass deserves attention. And any eGFR below 60 should prompt a conversation with your doctor about additional testing.

Additional tests that can help clarify the picture include cystatin C, which is a kidney function marker that is not influenced by muscle mass and provides a more accurate assessment of filtration in muscular individuals. A urinalysis looking for protein or blood in the urine can detect kidney damage that creatinine alone might miss. And a urine albumin-to-creatinine ratio (UACR) can identify early kidney damage before it shows up on standard blood work.

If you are on TRT and your creatinine has been slowly trending upward over time, the most likely explanation is increased muscle mass. But trending values should still be tracked and discussed with your provider. A gradual, modest increase that correlates with gains in lean body mass is different from a sudden jump that occurs without a change in body composition.

The CKD Staging System Explained

Chronic kidney disease is classified into five stages based on eGFR values. Stage 1 means your eGFR is 90 or above with some evidence of kidney damage (like protein in the urine). Stage 2 is an eGFR of 60 to 89 with evidence of damage. Stage 3 is split into 3a (eGFR 45-59) and 3b (eGFR 30-44). Stage 4 is an eGFR of 15 to 29, and Stage 5 is below 15, which is where dialysis or transplant becomes necessary.

Most people who get flagged on routine blood work fall into Stage 1 or Stage 2, and in many of these cases, especially among active individuals with higher muscle mass, the reduced eGFR is an artifact of the calculation rather than true kidney impairment. This is why additional testing with cystatin C or urinalysis is so valuable for distinguishing between a calculation issue and genuine kidney disease.

For men on TRT or other hormone therapies, it is worth knowing that certain medications commonly used alongside TRT can affect kidney function. NSAIDs (like ibuprofen) taken regularly can damage the kidneys over time. Some blood pressure medications affect kidney filtration. And high doses of certain supplements can add to the kidneys' workload. Being aware of these factors and discussing them with your provider helps ensure that your kidney health is properly monitored and protected.

Practical Steps for Monitoring Kidney Health

If you are on TRT or any hormone protocol, make kidney markers a standard part of your monitoring panel. Track creatinine and eGFR over time and look at trends rather than isolated values. If your creatinine is mildly elevated and you are muscular, ask your doctor about cystatin C testing to get a more accurate picture. Stay well hydrated, especially around the time of blood draws, as dehydration can temporarily elevate creatinine. And if you use creatine supplements, note this on your lab orders so your provider can factor it into their interpretation.

Kidney health is one of those things that is easy to take for granted until there is a problem. By understanding what your blood work actually means and knowing when to investigate further versus when a finding is benign, you can protect your kidney health while avoiding unnecessary worry over values that are explained by your body composition and supplement use.

Protecting Your Kidney Health on TRT and Beyond

Beyond understanding what your lab values mean, there are practical steps you can take to actively protect your kidney health while on TRT or any hormone optimization protocol. Hydration is foundational. Your kidneys need adequate water to filter waste products efficiently. Chronic mild dehydration, which is more common than most people realize, makes your kidneys work harder and can contribute to elevated creatinine levels independent of any actual kidney damage. Aiming for a urine color that is pale yellow throughout the day is a simple and practical indicator of adequate hydration.

Blood pressure management is critically important for kidney health. The kidneys are highly vascular organs, and chronically elevated blood pressure damages the small blood vessels within them over time. TRT can contribute to blood pressure increases in some men, particularly through fluid retention or increased red blood cell mass. Regular blood pressure monitoring, both at home and during medical visits, helps catch elevations early before they have time to cause organ damage. Target blood pressure for kidney protection is generally below 130/80 mmHg.

NSAIDs deserve special attention because many active men use them regularly for pain management without realizing the cumulative kidney risk. Ibuprofen, naproxen, and similar anti-inflammatory drugs reduce blood flow to the kidneys and can cause direct kidney damage with chronic use. Occasional use for acute pain is generally fine for people with healthy kidneys, but daily or near-daily NSAID use is a significant risk factor for kidney problems. Acetaminophen, while not without its own risks, is generally considered safer for the kidneys and may be a better choice for regular pain management needs.

Annual thorough blood work that includes kidney markers, a urinalysis, and blood pressure measurement creates a longitudinal record that makes it easy to spot trends. A single creatinine value is a snapshot, but tracking the trend over years tells a much more meaningful story. Catching a gradual upward trend in creatinine or a downward trend in eGFR early gives you and your provider time to investigate and intervene before any significant damage accumulates. Prevention and early detection are always cheaper, easier, and more effective than treating established kidney disease.

Research on Creatinine, eGFR, and Muscle Mass Confounders

The relationship between creatinine and muscle mass is well-documented and frequently causes false alarm on blood work. A 2017 study in the Clinical Journal of the American Society of Nephrology analyzed data from over 9,000 adults and found that men with higher muscle mass (measured by DEXA) had creatinine levels that were 0.2-0.4 mg/dL higher and eGFR values that were 8-15 mL/min lower than their actual kidney function as measured by cystatin C, a kidney marker not affected by muscle mass. This means a muscular man on TRT with a creatinine of 1.3 mg/dL and a calculated eGFR of 62 mL/min might have a true GFR of 75-80 mL/min, well within the normal range. A 2019 study in the Journal of the American Society of Nephrology recommended using cystatin C-based eGFR equations for patients with extremes of muscle mass, including bodybuilders and patients on testosterone therapy. The CKD-EPI 2021 equation, which removed race as a variable, still uses creatinine and does not account for muscle mass directly. For TRT patients, requesting a cystatin C level alongside creatinine provides a more accurate kidney function assessment. A 2022 study in Kidney International Reports confirmed that creatine supplementation (common among men on TRT who also weight train) can raise serum creatinine by 0.1-0.3 mg/dL without any actual change in kidney function.