Creatinine, Creatine and Cancer – Separating Myth from Medicine (Part 1)
- Brainz Magazine
- 58 minutes ago
- 6 min read
Dr. Asha Martin is a medical oncologist and haematologist with over 10 years of experience. Based in St. Lucia with a special interest in breast, colon, prostate cancer, myeloma and anemias. Passionate about empowering patients with clear, practical health insights.
If you’ve ever had routine blood work, you’ve no doubt come across the term creatinine. As a medical oncologist, I’ve seen patients become quite anxious when they notice elevated or low creatinine, especially when they are already dealing with a cancer diagnosis or worried about one. In the world of oncology, many tests, numbers, and biomarkers give rise to worry, and creatinine is no exception. People ask, “Does this mean my cancer is worse?” or “Could my creatinine be the reason I developed cancer?”
In this article, I’ll walk you through what creatinine is, how it is measured, why it matters in general medicine and specifically in oncology, what the evidence shows about its relation to cancer, and most importantly, what it does not mean. My aim is to help you interpret data relevant to patients with cancer (or at risk of cancer), provide perspective, and separate myth from medicine.
What is creatinine?
Let’s start at the basics. Creatinine is a breakdown product of creatine, a molecule found primarily in muscle and used for energy storage and metabolism in tissues that require bursts of energy (like skeletal muscle). As muscles break down creatine and creatine phosphate, one of the waste products is creatinine. The kidneys filter creatinine (via glomeruli), and some amount is secreted by tubular cells. The end result is that serum creatinine serves as a widely used marker of kidney function.
When the kidneys are functioning normally, creatinine is produced at relatively steady rates (dependent on muscle mass and diet) and is cleared by the kidneys and appears in the urine. If creatinine builds up in the blood, that may be a sign of reduced kidney clearance. On the other side, very low creatinine may reflect low muscle mass and low creatinine production.
Some broad take-homes about creatinine:
It is influenced by muscle mass, diet (especially meat intake), age, sex, and ethnic factors.
It is used as part of the equation to estimate glomerular filtration rate (eGFR), a measure of kidney filtration.
Elevated creatinine commonly prompts investigation of kidney disease.
Very low creatinine is less often discussed, but in certain settings may signify low muscle mass or decreased production.
So far, nothing specific to cancer. But given that cancer patients often have issues with kidney function (either pre-existing or from treatments), or with muscle wasting (cachexia), creatinine becomes relevant in the oncology setting.
Why creatinine matters in cancer patients
There are a number of reasons why creatinine gains relevance when we look at cancer and oncology patients.
Kidney function and treatment tolerance: Many cancer therapies, including chemotherapy, targeted therapies, immunotherapy agents, and radiopharmaceuticals, are cleared by the kidneys or can affect kidney function. If the kidneys are not functioning well (elevated creatinine), then drug dosing may need to be modified, and risks of toxicity may increase. Some newer targeted cancer therapies can cause rises in creatinine via inhibition of the tubular secretion of creatinine, even when glomerular filtration is preserved. Thus, in oncology we ask, is the creatinine rise due to declining kidney function (glomerular or tubular), or is it due to other factors (muscle mass, diet, drug interference)?
Muscle mass, cachexia, and prognosis: In many cancer patients, especially with advanced disease, muscle wasting (sarcopenia) is a common problem. Low muscle mass means lower production of creatinine, all else being equal. Some studies have shown that low creatinine (or low creatinine relative to other markers) is associated with worse outcomes in cancer. Therefore, creatinine can serve, imperfectly, as a surrogate of muscle mass and by extension general physiological reserve.
Prognostic associations: Some research shows that both high and low creatinine levels are associated with worse survival in certain cancer patient cohorts, including colorectal cancer. That does not mean creatinine causes worse cancer outcomes, it may simply reflect underlying physiology (kidney problems, muscle wasting, comorbid illness) that correlates with poorer prognosis.
Interpretation nuance in oncology: Because many factors (kidney disease, hydration status, muscle mass, diet, tumour burden, treatments) influence creatinine, interpreting a concerning creatinine number in a cancer patient always demands context. A rising creatinine may mean kidney injury (from tumour, treatment, dehydration), or it may be drug-related, or it may be benign relative to muscle mass changes. Therefore, separating myth from medicine means being precise about what the number represents, what it does not, and how it ties into your overall clinical picture.
What the evidence shows: creatinine and cancer
Here’s where we dive into some of the research and what it tells us, and importantly, what it does not tell us, about the relationship between creatinine and cancer.
High or low creatinine and overall survival in cancer
A large retrospective study in colorectal cancer found that both high serum creatinine (Scr) and low Scr were associated with worse overall survival compared to normal Scr levels. For example, patients with low Scr had HR -1.37 and those with high Scr had HR -1.78 relative to normal.
In short, having creatinine outside of the normal range in either direction correlated with a poorer prognosis.
Similarly, in a cohort of patients with various cancers at end-of-life, both low and high Scr were significant for shorter survival.
Importantly, these associations are not proof that creatinine itself is driving cancer progression. Rather, they suggest that abnormal creatinine levels may act as a marker of worse physiological status (kidney dysfunction, muscle mass loss, comorbidities), which in turn correlates with poorer outcomes.
Creatinine-cystatin C ratio and muscle mass/prognosis
A clever study looked at the ratio of serum creatinine to cystatin C (another kidney marker less dependent on muscle mass) and found that a higher ratio, meaning relatively more creatinine vs. cystatin C, was associated with better short-term mortality (6-month and 1-year) in cancer patients at diagnosis.
Why? Because lower muscle mass means lower creatinine production, cystatin C production is less muscle-dependent. So a low ratio may flag sarcopenia or frailty, which in oncology is bad. This gives us a glimpse into how creatinine may indirectly reflect muscle reserve and thus prognosis.
Creatinine, kidney disease and cancer risk
Another angle: what about creatinine (and kidney function) as a risk factor for developing cancer? A population cohort found that using cystatin C, a sensitive kidney marker, mild kidney disease was associated with a modest increase in cancer incidence (about 4 percent) and a more pronounced increase in cancer mortality (about 15 percent) in mild disease, rising to about 19 percent and 48 percent in advanced kidney disease.
Interestingly, the study notes that serum creatinine alone did not identify the same associations as cystatin C did. This highlights a key nuance, kidney function is relevant to cancer risk and outcomes, but creatinine alone may not suffice as the marker.
Creatinine and specific cancers
In one metabolomics study of colon versus rectal cancer, higher plasma creatinine was associated with about 39 percent increased all-cause mortality in rectal cancer but not colon cancer.
In lung cancer risk in men, higher quartile serum creatinine showed a negative association, meaning higher creatinine was associated with lower risk, among former and ever smokers in one analysis.
For prostate cancer, an older study suggested higher normal-range creatinine might double risk, but this remains early, and interpretation is complex.
These studies illustrate that the relationships vary by cancer type, patient population, level of kidney and muscle function, and whether creatinine is used as a static value or in relation to other markers.
Creatinine rises due to cancer therapies
A practical clinical point, many targeted cancer treatments and newer agents can raise serum creatinine without actual worsening of glomerular filtration. They may inhibit tubular secretion of creatinine or otherwise interfere with creatinine kinetics.
What that means, in a patient on such treatment, a rising creatinine may not always signify true kidney injury, and misattributing it could lead to inappropriate treatment changes. Awareness of drug-induced creatinine changes is critical in oncology.
Separating myth from medicine: What creatinine isn’t
Because creatinine shows up in many contexts and patients often worry about bad numbers, let’s clarify what it is not in the cancer context.
Creatinine is not a cancer marker in the sense of something you measure to detect cancer, unlike PSA for prostate or CA 125 for ovarian.
A normal creatinine does not guarantee you do not have cancer or that your kidney is unaffected in subtle ways.
Conversely, an elevated creatinine is not inherently an indicator of cancer progression unless there is a clear mechanistic link, such as a tumour compressing or invading the kidney.
A change in creatinine in an oncology patient should not immediately be attributed to cancer worsening without exploring other causes (hydration, muscle mass, therapy effect, kidney injury, obstruction, etc.).
Adjusting cancer treatment purely on the basis of creatinine without full assessment may lead to suboptimal therapy.
In short, treat creatinine as a piece of the puzzle, important, but not singularly determinative.
Read more from Dr. Asha Martin
Dr. Asha Martin, Medical Oncologist and Clinical Haematologist
Dr. Asha Martin MD DM (Haem-Onc) is a passionate Medical Oncologist and Clinical Haematologist with over a decade of experience, now practicing in St. Lucia. Focusing on breast, colon, and prostate cancers, multiple myeloma, and anemias, she balances her work at the island’s main public hospital with her private practice. Driven by a mission to empower patients, she launched Sabinearose.com in 2025, offering clear, practical health insights. When not treating patients, she writes to demystify cancer care, because knowledge is the first step to healing.
