High Creatinine: When Your Kidneys Are Behind It and When It Is Muscle, Creatine or Meat
Creatinine is produced in your muscles and excreted by your kidneys. A high value can point to reduced filtering capacity, but also to a lot of muscle mass, creatine, a meat meal, hard training or dehydration. Cystatin C and urine albumin can show which of these applies.
A red arrow next to creatinine feels like a verdict on your kidneys. First of all, it is a question. Sometimes the answer is your kidneys. Often it is muscle, creatine, steak or training. Both deserve a calm second look.
Do you know that moment? You open your lab report, scroll through numbers that mean little to you, and your eyes catch on a red arrow.
Creatinine. High. Below it, perhaps an eGFR that is lower than last time.
And your mind does what minds do in moments like this. It starts searching online. Kidney disease. Dialysis. Why did I not notice anything?
The red arrow, two days after leg day
Imagine: on Monday you got through the hardest leg workout of the month. Squats, lunges, trembling thighs at the end. In the evening you had a big steak, because muscles need protein, after all. And for a few weeks now, you have also been taking creatine.
On Wednesday morning, the results of your checkup arrive. There is a red arrow next to creatinine. Your eGFR is below your last value.
I know this pattern very well. At a follow-up after a few quieter days, without meat before the blood draw and with cystatin C and a morning urine sample added, the picture often looks different. Creatinine is back within the reference range, cystatin C is unremarkable, and there is no albumin in the urine.
Whether the training, the steak or the creatine tipped the scales cannot be reliably separated in an individual case. I cannot claim causality, I am describing a temporal association. And sometimes the follow-up confirms that the kidneys do need attention.
The lesson: A single creatinine value is a clue. It only becomes a diagnosis in context.
This is exactly the context we will now look at together. Without panic and without playing anything down.
What to expect in this article
- What creatinine is and where it comes from
- Why eGFR is an estimate
- Muscle, creatine and meat as influences
- Training, dehydration and medications
- Cystatin C as a second witness
- Urine albumin as an early signal
- Real warning signs you should not wait out
- Three levers for your next blood test
What is creatinine, and why does it end up in your blood?
Perhaps you have always thought of creatinine as a pure kidney value. That is understandable. After all, on your lab report it is usually listed with the kidney values.
Its story, however, begins in the muscle. Your muscle cells store energy as creatine phosphate. Imagine it as a turbo battery that instantly delivers fresh energy with every short, hard effort.
Every day, a small part of this store breaks down into creatinine on its own. Creatinine is, so to speak, the empty battery casing. Your body has no further use for it and sends it off for disposal.
Disposal runs through the kidneys. Their fine filter clusters, the glomeruli, sieve creatinine out of the blood. A smaller part is also actively released into the kidney tubules, a kind of side exit.
So your blood value is always a balance between two quantities. How much creatinine is produced? And how much do the kidneys excrete? If production rises, the value rises, even if your kidneys filter flawlessly.
A team around the Liège nephrologist Pierre Delanaye summarized why creatinine is not a simple value. Besides the side exit into the kidney tubules, muscle mass and protein intake influence the blood level, and the measurement method and natural fluctuations add to this. Because the relationship between creatinine and filtering capacity is hyperbolic, small fluctuations hit the calculated eGFR hard, especially when kidney function is good.
For you, this means: with healthy kidneys, a small upward blip can create a big dent in your eGFR.
Delanaye P, Cavalier E, Pottel H. Nephron. 2017. DOI: 10.1159/000469669From a KPNI perspective, creatinine is first and foremost a metabolic signal. It tells you something about your muscle metabolism before it reveals anything about your kidneys. The hormonal system plays a part too. According to a review in the Journal of Internal Medicine, cortisone and active vitamin D preparations may alter the production or release of creatinine.
Creatinine is not a pure kidney value. It is a muscle value that your kidneys excrete. If you have a lot of muscle, you produce more of it. If you have little muscle, you produce less. In that case, weaker kidneys can even stay hidden behind a reassuring number.
And now you know why the same creatinine value can mean something entirely different in two people.
eGFR: Why your lab report contains an estimate
Below the creatinine there is usually a second number, the eGFR. It sounds precise, complete with a unit and all the trimmings. If it slips below 90, it feels like being relegated to a lower league.
The small e stands for estimated. The eGFR is not a measurement of your filtering capacity. It is a calculation based on your creatinine, your age and your sex. The result is expressed relative to a standard body surface area of 1.73 m².
Imagine a weather forecast that estimates the rain for all of Berlin from the air pressure outside your window. Most of the time it gets it about right. On days with a thunderstorm right above your street, it is off.
In 2021, a research team around the Boston nephrologist Lesley Inker developed new equations without the former race coefficient. They were based on ten studies with 8,254 participants. The equations were then tested in twelve further studies with 4,050 people, against directly measured filtering capacity. At least 85 percent of the estimates were no more than 30 percent off the measured value, and the combination of creatinine and cystatin C was more accurate than creatinine alone.
For you, this means: eGFR is a good tool for many people. For up to one in seven people, however, it was off by more than 30 percent.
Inker LA et al. N Engl J Med. 2021. DOI: 10.1056/NEJMoa2102953GFR categories according to KDIGO 2024, in mL/min per 1.73 m²
Without other signs of kidney damage, G1 and G2 do not meet the criteria for chronic kidney disease. Source: KDIGO guideline 2024.
According to the KDIGO 2024 guideline, chronic kidney disease is only present when abnormalities persist for at least three months. These include an eGFR below 60 or signs of kidney damage, such as urine albumin of 30 mg/g or more. The guideline itself notes that eGFR lags behind changes and can be distorted by factors outside the kidney.
So if a value is abnormal, do not just ask: how high is the number? Ask as well: under what conditions was it measured?
An eGFR of 75 in a muscular person after leg day and an eGFR of 75 in a frail person are two different stories. The formula does not know your muscles. You do.
And now you know why eGFR is a good starting point for the conversation, not an end point.
When muscle, creatine, meat or training drive the value up
This is where it gets personal for many active people. Because the very things you do for your health can push the value up.
I will go through the most common influences one by one. For each one, we look at this: does it only shift the number, or does it also put demands on the kidneys?
Muscle mass: bigger engine, more exhaust
A big engine produces more exhaust than a small one, without anything being broken in the tailpipe. In the same way, a lot of muscle mass produces more creatinine.
A research group from São Paulo examined 170 healthy adults and measured their body composition. Creatinine in blood and urine was clearly linked to lean body mass, whereas cystatin C was not. The very physically active participants had an average creatinine of 1.04 instead of 0.95 mg/dL, while there was no difference in cystatin C.
For you, this means: if you have a lot of muscle, a slightly high value may simply be your personal normal.
Baxmann AC et al. Clin J Am Soc Nephrol. 2008. DOI: 10.2215/CJN.02870707This is why the KDIGO 2024 guideline explicitly lists extreme sports and bodybuilding as situations in which creatinine alone can be inaccurate.
Creatine: a full battery leaves more empty casings
Creatine is one of the best studied supplements in strength sports. It fills the creatine phosphate store in your muscles. And a full store breaks down into more creatinine.
A team from the Federal University of São Paulo pooled 26 randomized trials with 1,036 participants. With creatine, serum creatinine rose by an average of 0.14 mg/dL, and the creatinine-based estimate of filtering capacity fell by around 11 mL/min. When filtering capacity was measured directly with the Cr-EDTA method, however, no deterioration was found.
For you, this means: with creatine, the calculation can falsely suggest weaker kidneys. Directly measured function remained stable in these studies.
de Souza Almeida A et al. Int Urol Nephrol. 2026. DOI: 10.1007/s11255-026-05287-xA second meta-analysis from Thessaloniki with 19 randomized trials arrived at a similar picture in 2026: creatinine on average 0.13 mg/dL higher, with no significant difference in urea and eGFR. The authors stress that randomized trials lasting more than one year are still lacking.
A randomized trial from São Paulo shows what this looks like in strength sports. People who did regular strength training and ate a high-protein diet took creatine or a placebo for twelve weeks. Filtering capacity measured with Cr-EDTA remained stable in both groups, and albumin and protein in the urine barely changed. The same research group found a similar result in people with type 2 diabetes.
A case report from England describes how strong the effect can be in an individual. A man who did strength training was taking a creatine ethyl ester product, and his creatinine reached values that would fit advanced kidney disease. After he stopped taking it, the changes receded, and his kidney function was judged to be normal.
In all honesty, this is part of the picture too: the KDIGO guideline names creatine supplements from bodybuilding as an example of supplements that have been linked to an allergic inflammation of the kidney tissue. It does not give frequencies. If you have kidney disease, discuss creatine with your doctor beforehand.
Cooked meat: creatinine from your plate
Meat is muscle, and muscle contains creatine. When meat is fried or boiled, part of it is converted into creatinine. Your gut absorbs it, and it ends up directly in your blood.
A British team gave 32 people a meal with cooked meat and, for comparison, a meat-free meal. One to two hours after the meat, median creatinine rose from 80.5 to 101 µmol/L, and eGFR fell from 84 to 59.5. The meat-free meal barely changed the values, and cystatin C remained largely unaffected.
For you, this means: a steak shortly before your blood test can push you below the threshold of 60 on paper for a few hours.
Preiss DJ et al. Ann Clin Biochem. 2007. DOI: 10.1258/000456307779595995A British study with 80 participants added two important details. After the meat meal, six of 16 people with stage 3a kidney disease would have been wrongly classified as stage 3b. After twelve hours of fasting, the effect had disappeared in everyone.
As early as 1983, researchers measured an average 52 percent rise in plasma creatinine in six healthy men after 225 grams of cooked meat. Creatinine clearance, a measure of filtering capacity, stayed the same.
Hard training: when muscle loses its building blocks
After a really hard leg day, every staircase feels like a mountain. Behind this are tiny injuries in the muscle fibers, which your immune system then cleans up.
A team from São Paulo had 58 healthy adults complete a single high-intensity strength session. In the men, creatinine rose slightly but measurably after 24 hours, from about 1.03 to 1.10 mg/dL, while in the women it remained stable. Three men even formally met the KDIGO criteria for acute kidney injury. The kidney stress markers in the urine rose after two hours and were back at baseline after 24 hours.
For you, this means: a very hard session the day before can visibly shift your value, and in the short term your kidneys may actually be under stress.
Spada TC et al. PLoS One. 2018. DOI: 10.1371/journal.pone.0205791In 22 people after a marathon, creatinine rose so sharply in 82 percent that it formally corresponded to stage 1 or 2 acute kidney injury. The peak came right after the race, and the next day the values were lower again. In the urine, the researchers found signs of strain on the kidney tubules in 73 percent. So part of the rise reflects genuine strain and not just measurement noise. Whether this strain leaves no lasting effects is something larger studies with longer follow-up still need to clarify.
The contrasting finding from Massachusetts is fascinating. There, 203 volunteers performed 50 maximal eccentric, that is braking, movements with their elbow flexors. Creatine kinase, a marker of muscle damage, was on average more than 60 times higher after four days than before, and above 10,000 U/L in 51 people. The kidney function measures, including creatinine, did not rise significantly.
So sore muscles alone do not automatically mean kidney stress. It depends on how much muscle is involved, how long you exert yourself, and how much heat and fluid loss come on top.
Dehydration: when the filter runs on low
When you are short of water, your body starts to save. During exertion and heat, blood flow to the kidneys can drop so that muscles and skin get enough. The filter then runs on low.
Researchers from Nijmegen had 35 young men exercise at about 80 percent of their maximum heart rate until they had lost around three percent of their body weight in fluid. The filtering capacity estimated with cystatin C fell from 118 to 103 mL/min, whereas after a short session it was unchanged. The kidney stress marker NGAL in the urine rose.
For you, this means: when you are dehydrated, your filtering capacity can actually drop in the short term. This is not just a measurement error, but a sign that your body is saving water.
Bongers CCWG et al. Physiol Rep. 2018. DOI: 10.14814/phy2.13734A crossover study from Buffalo shows that heat and fluid loss can add up. In 13 healthy adults, kidney stress markers such as albumin and NGAL in the urine rose most when they exercised in the heat and neither drank nor were cooled. A review by the same group describes how heat can throttle blood flow to the kidneys. The exact mechanisms, however, come mainly from animal models and have not yet been conclusively demonstrated in humans.
How much drinking makes sense, and why more is not automatically better, is something I explain in the article on kidneys and water.
Medications: when the side exit gets narrowed
Remember the side exit, the active release of creatinine into the kidney tubules? Some medications narrow exactly this exit. Creatinine then builds up in the blood, even though the filter is working just as well as before.
The team around Pierre Delanaye summarized what the antibiotic trimethoprim does to creatinine. Even at usual doses, it slows the release of creatinine into the kidney tubules. Creatinine rises quickly but reversibly, independently of filtering capacity, and creatinine-based formulas then show an eGFR that is too low.
For you, this means: while you are taking an antibiotic such as co-trimoxazole, your creatinine can rise even though your filtering capacity stays the same. The second component, sulfamethoxazole, can however strain the kidneys themselves at high doses. That is why interpreting this belongs in medical hands.
Delanaye P et al. Nephron Clin Pract. 2011. DOI: 10.1159/000328911An older review also names cimetidine, pyrimethamine and salicylates, which can slow this exit as well. The situation is quite different with painkillers such as ibuprofen or diclofenac. They do not just change the number. According to the KDIGO guideline, they can actually lower filtering capacity by reducing blood flow to the kidneys. Taking such painkillers after training, combined with little fluid, can put a double load on your kidneys. Talk to your doctor about this if you take them regularly.
Lab technique: when the sample has to wait
The value can also drift in the lab. Many laboratories measure creatinine with the Jaffé method, a color reaction. It also reacts to other substances, such as glucose, ketone bodies or some antibiotics from the cephalosporin group.
The KDIGO guideline therefore recommends using enzymatic methods where possible and separating the serum from the blood cells within twelve hours. If a sample sits unseparated for a long time, the Jaffé value can rise over time. If you eat a ketogenic diet or are currently fasting, ask which method your lab uses.
Points more to a false alarm
- Very hard training the day before or the same day
- Cooked meat shortly before the blood draw
- Taking creatine or having a lot of muscle mass
- Medications such as trimethoprim or cimetidine
- Cystatin C unremarkable, no albumin in the urine
- Value drops when retested under standard conditions
Points more to the kidneys
- Elevation persists under standard conditions
- The estimate using cystatin C is also low
- Urine albumin of 30 mg/g or more, confirmed in morning urine
- Blood in the urine on repeated tests
- High blood pressure, diabetes or heart disease
- eGFR keeps falling over months
Many influences that push the value up are signs of an active life: muscle, training, protein. In that case, the cause often lies not in your kidneys but in the timing of the test. At the same time, heat, dehydration and extreme exertion can genuinely strain the kidneys. Both are true.
And now you know why the two days before your blood test sometimes have more say over your value than your kidneys do.
Cystatin C: the second witness
Imagine a courtroom. A single witness who partied all night before testifying is not necessarily lying. But you would like to hear a second one.
Cystatin C is that second witness. It is a small protein that almost all body cells produce at a steady rate, not just the muscles. The kidneys also filter it out of the blood. That is why it reveals a lot about filtering capacity, but depends less on your muscles and your plate.
The international kidney guideline KDIGO 2024 recommends estimating filtering capacity from creatinine and cystatin C together when a creatinine-only estimate may be inaccurate and a clinical decision depends on it. Among the situations it lists are extreme sports and bodybuilding, a high-protein diet, creatine supplements and medications that slow creatinine excretion. In large studies, the combined estimate was within 30 percent of the measured value in around 90 percent of people.
For you, this means: if you train a lot or take creatine, cystatin C is the obvious question to put to your doctor.
Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. Kidney Int. 2024. DOI: 10.1016/j.kint.2023.10.018An international research group led by Michael Shlipak from San Francisco pooled data from 16 cohorts with more than 93,000 people. With cystatin C, more people in the general population had an eGFR below 60, namely 13.7 instead of 9.7 percent. At the same time, risk assessment became more accurate, clearly so for the risk of death and more narrowly for kidney failure.
For you, this means: cystatin C can also identify people whose creatinine looks too friendly.
Shlipak MG et al. N Engl J Med. 2013. DOI: 10.1056/NEJMoa1214234But cystatin C is not a perfect witness either. In an analysis of 8,058 people from Groningen, cystatin C was higher in older people, in men, with higher body weight, with greater height, in smokers and with elevated levels of the inflammation marker CRP, independently of kidney function. From a KPNI perspective, this is fascinating: an immune system activated by inflammation can influence the second witness. Cortisone can also distort the estimate, according to the KDIGO guideline.
If your creatinine value is unclear, ask specifically for cystatin C and for the combined eGFR from both values. It is important that both values come from the same blood sample, as the guideline also recommends.
When two independent witnesses say the same thing, the testimony becomes strong. When they contradict each other, that is not chaos but a lead. Then it is worth asking about muscle, medications, inflammation or cortisone.
And now you know why a second marker often brings more clarity than the third repeat of the same value.
Urine albumin: the signal creatinine does not show
Maybe your creatinine is entirely unremarkable, and you feel you are on the safe side. This is exactly where a look at your urine is worthwhile.
A healthy kidney filter holds back large proteins such as albumin. Imagine a coffee filter: the water runs through, the grounds stay inside. If the filter develops fine cracks, grounds slip through, even though the water still runs through quite normally.
In the same way, albumin can appear in the urine while eGFR is still unremarkable. It is measured as the albumin-to-creatinine ratio, ACR for short, usually from a simple urine sample.
mg/g, category A1: normal to mildly increased
mg/g, category A2: moderately increased
mg/g, category A3: severely increased
Albuminuria categories according to KDIGO 2024. In mg/mmol, they roughly correspond to the ranges below 3, 3 to 30 and above 30.
The Chronic Kidney Disease Prognosis Consortium analyzed data from 105,872 people in 14 population studies with urine ACR. The risk of death rose steadily with ACR, with no recognizable threshold, and was already increased from about 10 mg/g. eGFR and ACR predicted risk independently of each other.
For you, this means: a good eGFR without a urine test is only half the information.
Chronic Kidney Disease Prognosis Consortium, Matsushita K et al. Lancet. 2010. DOI: 10.1016/S0140-6736(10)60674-5This is why the KDIGO guideline recommends testing people at risk of kidney disease with both tests: urine albumin and filtering capacity.
Urine has its false alarms too. Exercise, infections, menstruation and blood in the urine can raise ACR. A lot of muscle mass and a high-protein diet, on the other hand, increase urine creatinine and can make the ratio appear too low. That is why an elevated ACR should be confirmed with a first morning midstream urine sample.
If your lab report only contains creatinine and eGFR, ask for the albumin-to-creatinine ratio in a morning urine sample. Especially if you have high blood pressure, diabetes or heart disease. Do not give the sample right after a hard session.
A normal eGFR is reassuring. But a kidney can quietly lose protein while creatinine still looks entirely unremarkable. That is why the urine test is not an extra for worriers, but the second half of the picture.
And now you know why a cup of morning urine sometimes reveals more than a whole blood panel.
Real warning signs: when you should not wait
Up to this point, a lot of this sounds reassuring. It is meant to. But I do not want you to explain away a real alarm just because you trained the day before.
Your kidneys are quiet organs. The KDIGO guideline stresses that reduced filtering capacity and albumin in the urine usually cause no symptoms and often only become visible in the lab. According to data from the Global Burden of Disease study, which the guideline cites, around 9.1 percent of people worldwide had chronic kidney disease at some stage in 2017.
- Rapid rise: creatinine rises by 0.3 mg/dL or more within 48 hours, or to 1.5 times the baseline value within seven days. This is how the KDIGO guideline defines acute kidney injury.
- Dark urine after training: very dark urine the color of cola or tea, especially with severe muscle pain or swelling. This needs to be checked the same day.
- Little urine: clearly less urine than usual, even though you are drinking.
- Protein or blood in the urine: an ACR of 30 mg/g or more, confirmed in morning urine, or blood repeatedly detected in the urine.
- Confirmed low filtering capacity: an eGFR below 60 that is confirmed under standard conditions and with cystatin C, or an eGFR that keeps falling over months.
- Risk factors: the KDIGO guideline names high blood pressure, diabetes and heart disease as the most important reasons to take a targeted look at the kidneys.
A team from Oslo followed 136 people with exertional rhabdomyolysis, that is severe muscle breakdown after exercise. In 78 percent of them, strength training was the trigger. Five developed acute kidney injury, and all five already had elevated creatinine on admission. No one with normal creatinine on admission developed kidney injury.
For you, this means: after extreme training, your creatinine value is an important safety marker, not a detail.
Vangstad M et al. BMJ Open Sport Exerc Med. 2026. DOI: 10.1136/bmjsem-2026-003214A review in the New England Journal of Medicine describes rhabdomyolysis as a condition in which components of breaking down muscle, such as myoglobin, can damage the kidneys. This should be taken seriously. And it is exactly why dark urine after training is not a detail.
And then there is your nervous system. A red arrow can trigger a real stress response, with a pounding heart, rumination and poor sleep. That is understandable. But fear makes a poor lab doctor. A clear plan for the follow-up test can often calm you more than any search engine.
This is not about a number on paper. It is about freedom.
You are allowed to train with power without flinching at every arrow. And at the same time, you are allowed to protect an organ that quietly filters for you every day.
Reassurance and vigilance are not mutually exclusive. A false alarm is only a false alarm once the follow-up test shows it to be one.
And now you know which signs you should take seriously, even if you have only just trained.
Three levers for a meaningful next blood test
You cannot control the next measurement. But you can make sure it gets a fair chance.
Create standard conditions
Do not have blood drawn right after leg day. In the studies, the peak of the rise came directly after exertion or the following day. There is no firm rule for this, but two to three quieter days before the follow-up test are a sensible direction.
Do not eat cooked meat before the blood draw. Ideally, come fasting and with at least twelve hours since your last meat meal. Drink normally, not excessively, and do not arrive at the lab dehydrated.
Share the context
Tell your doctor whether you take creatine or protein powder, how much you train and which medications you take, including painkillers and antibiotics. Do not stop any of them without talking to your doctor first.
Ask for cystatin C from the same sample, for the albumin-to-creatinine ratio in morning urine, and whether your lab uses an enzymatic method. Whether you pause creatine before a follow-up test is something you decide together. With cystatin C, interpretation can also work without a pause.
Trends instead of snapshots
The KDIGO guideline recommends repeating an incidentally abnormal value before kidney disease is diagnosed. Chronic kidney disease requires abnormalities to persist for at least three months.
Collect your lab reports, compare values from the same lab where possible and pay attention to the direction. For the warning signs above, the opposite applies: do not wait, get them checked promptly.
Your kidneys are among your most important detox organs. They do not need a cleanse, but conditions in which they can work well. These include adequate fluid, well controlled blood pressure, stable blood sugar and a mindful approach to painkillers.
And now you know how to turn your next blood test into an answer instead of a new puzzle.
What is established and what remains open
Established by guideline, meta-analyses and controlled studies: creatine can shift serum creatinine and creatinine-based eGFR without directly measured filtering capacity declining in the studies. Cooked meat can clearly raise creatinine for several hours. Cystatin C depends less on muscle mass, and the KDIGO guideline recommends the combined estimate when creatinine alone may be unreliable. Urine albumin predicts risk independently of eGFR.
Smaller studies, not yet conclusive: how strongly and for how long hard strength training, marathons, heat or dehydration shift the values is based on studies with 13 to 203 people. The mechanisms of heat-related kidney strain come mainly from animal models.
Still open: randomized trials on creatine lasting more than one year are lacking. Whether repeated short peaks of strain harm the kidneys in the long run has not been clarified in humans.
What I observe clinically: many active people with a lot of muscle mass are alarmed by an eGFR just below 90 that can be put into context well under standard conditions and with cystatin C. This is experience, not a study.
A high creatinine value is first of all an invitation to take a closer look. Your muscles, your plate, your training and your kidneys tell a story together. If you read them together, you can recognize false alarms without overlooking a real warning.
More from the Detox Guide
Keep reading in the guide
- Kidneys and water: how much to drink?
- Detox after antibiotics and medications
- Liver detox without the marketing
- Phase 1 and phase 2 of liver detox
- Glutathione and detox
- Detox programs, juice cleanses and detox teas
- Fasting and autophagy
- The gut and elimination
- Gentle detox in everyday life
- Bitter compounds and digestion
- Stimulating the lymphatic system
- Sweating and sauna
- Alcohol and the liver
- Tired despite a healthy diet
- Sulforaphane and broccoli
- Foods for the detox phases
- Detox through the skin
- Alkaline cleanses and overacidity
- Tongue coating and bad breath
- Microplastics in the body
- Pesticides on fruit and vegetables
Where this topic connects
Muscle, training and metabolism are closely linked to your kidney values. These articles go deeper into the neighboring levels.
Recovery after exercise
Why rest is part of training and what happens during recovery.
SportRecognizing overtraining
Which signals show that your body needs more recovery.
SportSarcopenia: muscle loss with age
Why muscle mass is so valuable as you get older.
SportStrength training for diabetes
How muscles can buffer blood sugar, a topic that also concerns your kidneys.
SportInsulin resistance and weight loss
Why a stable metabolism matters for many organs.
Weight lossExercise as medicine
What exercise can change at the cellular level.
SportFrequently asked questions
When is creatinine considered high?
Can strength training raise your creatinine level?
Does creatine raise creatinine, and does it harm the kidneys?
How long before a blood test should I avoid meat?
What is the difference between creatinine and eGFR?
When does a cystatin C test make sense?
What does the urine albumin-to-creatinine ratio tell you?
Which medications raise creatinine without lowering filtering capacity?
Can drinking too little distort your creatinine value?
When is a high creatinine value an emergency?
Does an eGFR between 60 and 89 already mean kidney disease?
What does a low creatinine value mean?
Sources
All studies were checked via PubMed against title, authors, year, journal and DOI, and key DOIs were additionally verified through the DOI registry. Statements from the KDIGO guidelines come directly from the guideline text. Figures on study results come from the respective abstracts, and the mean values of the strength training study from São Paulo from the full text. The study type is given in square brackets. For context: the data on creatine are based on meta-analyses of randomized trials, while the data on meat, training, heat and dehydration are based on smaller controlled studies and observational studies in humans. The mechanisms of heat-related kidney strain are based mainly on animal models.
- Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314. DOI: 10.1016/j.kint.2023.10.018 · PMID 38490803 [Consensus Guideline, KDIGO 2024]
- Khwaja A. KDIGO clinical practice guidelines for acute kidney injury. Nephron Clin Pract. 2012;120(4):c179-84. DOI: 10.1159/000339789 · PMID 22890468 [Consensus Guideline, summary of the 2012 KDIGO AKI guideline]
- Inker LA et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. N Engl J Med. 2021;385(19):1737-1749. DOI: 10.1056/NEJMoa2102953 · PMID 34554658 [Cohort, development and validation, n=8,254 and 4,050]
- Shlipak MG, Matsushita K, Ärnlöv J et al. Cystatin C versus creatinine in determining risk based on kidney function. N Engl J Med. 2013;369(10):932-43. DOI: 10.1056/NEJMoa1214234 · PMID 24004120 [Meta-analysis, k=16 cohorts, n=93,710]
- Chronic Kidney Disease Prognosis Consortium, Matsushita K et al. Association of estimated glomerular filtration rate and albuminuria with all-cause and cardiovascular mortality in general population cohorts: a collaborative meta-analysis. Lancet. 2010;375(9731):2073-81. DOI: 10.1016/S0140-6736(10)60674-5 · PMID 20483451 [Meta-analysis, k=14 cohorts with ACR, n=105,872]
- Delanaye P, Cavalier E, Pottel H. Serum Creatinine: Not So Simple! Nephron. 2017;136(4):302-308. DOI: 10.1159/000469669 · PMID 28441651 [Review]
- Baxmann AC, Ahmed MS, Marques NC et al. Influence of muscle mass and physical activity on serum and urinary creatinine and serum cystatin C. Clin J Am Soc Nephrol. 2008;3(2):348-54. DOI: 10.2215/CJN.02870707 · PMID 18235143 [Pathophysiology, cross-sectional study, n=170]
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This article is for information purposes and does not replace medical advice. It describes connections from research and clinical experience, not individual treatment instructions. If you have known kidney disease, diabetes, high blood pressure or heart disease, take medications or use supplements such as creatine, please discuss your values with a doctor in person. If you notice warning signs such as very dark urine, severe muscle pain after training or clearly less urine, seek medical help the same day.