High creatinine: what it means, the common causes and when to worry

A single high creatinine most often comes from muscle, a meat meal, creatine, dehydration or a medicine; a high result that holds on a clean retest and gives a low eGFR points to slower kidney filtration. Creatinine is a muscle waste product the kidneys clear at a fairly steady rate, so it builds up when filtration slows, which is why it is the kidney number on every basic metabolic panel. Three questions sort out a high result: is it new, does it hold on a clean retest, and what eGFR (estimated filtration rate, a kidney score worked out from creatinine, age and sex) does it give?

What counts as high creatinine

A creatinine result counts as high when it sits above the reference range printed on your report. A typical US adult lab range is roughly 0.74 to 1.35 mg/dL for men and 0.59 to 1.04 mg/dL for women, and women run lower mainly because they carry less muscle on average. Labs outside the US report creatinine in µmol/L: multiply mg/dL by 88.4 to convert, so 1.35 mg/dL is 119 µmol/L. The general guide to the marker, including what a low creatinine means, lives on the creatinine page.

Why a small rise can matter more than a big one

Creatinine and kidney filtration (GFR, the volume of blood the kidneys clean each minute) have an inverse, curved relationship. When filtration halves, creatinine roughly doubles, so at the healthy end of the curve a big drop in filtration moves creatinine only a little. A classic review in Clinical Chemistry found that GFR can fall by around half before serum creatinine rises above the reference range ⁵. So a creatinine that climbs from 0.8 to 1.2 mg/dL can mean a larger loss of filtration than one that climbs from 3.0 to 3.4.

Because of that curve, doctors read creatinine through eGFR, a number calculated from creatinine, age and sex. The 2021 CKD-EPI equation, now standard in US labs, does this without the race adjustment older versions used, and adding cystatin C to it makes the estimate more accurate ³. Kidney disease stages run from G1 (normal) to G5; G3a is an eGFR of 45 to 59 and G3b is 30 to 44 ¹. The same creatinine can land in very different places depending on who it belongs to.

There is no single creatinine that means stage 3 kidney disease. Stage 3 is an eGFR of 30 to 59 that lasts more than 3 months ¹, and the table shows a 70-year-old woman reaching it at a creatinine of 1.1 to 1.3 mg/dL while a 30-year-old man with 1.3 sits well clear. The eGFR page explains each stage.

CalculatoreGFR calculatorPut in your creatinine, age and sex to see the eGFR, and the stage, it gives.Work it out

Causes of high creatinine that are not kidney disease

The creatinine number and the health of the kidneys are separate questions. Anything that adds creatinine to the blood, or slows its exit without touching filtration, can push creatinine above range while the kidneys work normally. These are the usual explanations for a single high result in a healthy adult.

• More muscle. Bodybuilders and very muscular people make more creatinine and can sit above a range built on average bodies.
• Hard exercise. Heavy lifting or a long race in the previous 24 to 48 hours releases creatine from muscle.
• A cooked-meat meal. Cooking turns the creatine in meat into creatinine, which is why NICE advises no meat in the 12 hours before an eGFR blood test ⁴.
• Creatine supplements. Creatine breaks down to creatinine, so the blood number rises. In a 12-week trial of resistance-trained adults on a high-protein diet taking about 5 g a day, filtration measured with a precise tracer test did not fall ⁶. That trial was in healthy people; if you have kidney disease, ask a doctor before taking creatine.
• Dehydration. Heat, illness or not drinking concentrates the blood and slows flow through the kidneys; once rehydrated, creatinine usually settles within days. If you cannot keep fluids down, are passing little urine or feel faint or confused, get same-day care rather than rehydrating at home.
• Secretion-blocking medicines. Some drugs block the kidney's secretion of creatinine (the active pumping of creatinine into urine): trimethoprim (in co-trimoxazole), cimetidine, and the HIV drugs dolutegravir and cobicistat. They raise creatinine without lowering true filtration ¹.
• The lab method. The older Jaffe test (a chemical colour reaction) can read falsely high with ketones (fasting, diabetic ketoacidosis) and some cephalosporin antibiotics; newer enzymatic tests are less affected ¹.

The supplement that moves creatinine

Strong evidenceCreatineReliably raises serum creatinine because the body turns it into creatinine. In a 12-week trial in healthy trained adults, measured kidney function did not fall; people with kidney disease should ask a doctor before taking it.In our shop

When muscle or creatine might be the explanation, a cystatin C test helps, because muscle mass and diet barely move it. KDIGO 2024 advises using cystatin C, alone or combined with creatinine, when a creatinine-based eGFR is likely to be less accurate, for example with very high or very low muscle mass ¹. The trade-offs are set out in cystatin C vs creatinine, and the marker itself on the cystatin C page.

Causes of high creatinine that do involve the kidneys

Sudden: acute kidney injury

Acute kidney injury is a drop in kidney function over hours to days. The common causes are:

• Low blood flow to the kidneys, from vomiting, diarrhea, bleeding or severe infection (sepsis).
• Anti-inflammatory painkillers such as ibuprofen or naproxen, especially on top of dehydration.
• X-ray contrast dye.
• A blockage downstream, such as an enlarged prostate or kidney stones.
• Rhabdomyolysis, a breakdown of muscle after a crush injury or extreme exercise that releases myoglobin, which can damage the kidneys. Creatine kinase, the blood marker for it, climbs very high.

KDIGO sets the formal threshold (SCr means serum creatinine):

Increase in SCr by ≥0.3 mg/dl (≥26.5 μmol/l) within 48 hours; or Increase in SCr to ≥1.5 times baseline, which is known or presumed to have occurred within the prior 7 days; or Urine volume <0.5 ml/kg/h for 6 hours.KDIGO Clinical Practice Guideline for Acute Kidney Injury, 2012 ²

In hospital, doctors sometimes use the fractional excretion of sodium to tell low blood flow from damage inside the kidney; the FeNa calculator shows how it works.

Slow: chronic kidney disease

Chronic kidney disease (CKD) is a slow loss of filtration over months to years. Diabetes and high blood pressure cause most of it in the US, followed by glomerular disease (inflammation of the kidney's filters, sometimes from lupus) and polycystic kidney disease. KDIGO diagnoses CKD when an eGFR under 60, or a sign of kidney damage such as a urine albumin-to-creatinine ratio of 30 mg/g or more, lasts longer than 3 months ¹. Stages, outlook and treatment are on the chronic kidney disease page; the drivers have their own pages for type 2 diabetes and high blood pressure.

Reading high creatinine with your other results

A high creatinine on its own says little about the cause. The results printed next to it, or one or two added tests, usually point the way.

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How the trend tells sudden from slow kidney trouble

A doctor will ask for older results before reading a new high creatinine, because the baseline decides almost everything. A creatinine of 1.4 mg/dL that was 1.4 last year is a stable number to stage and follow. A creatinine of 1.4 that was 0.9 two days ago meets the KDIGO definition of acute kidney injury ². Find past results in your patient portal or old paperwork, and compare like with like: the same lab, the same time of day, the same habits beforehand. Small moves between draws are normal day-to-day variation.

Creatinine is a slow marker, so frequent rechecks of a normal value add little. People with diabetes or high blood pressure are usually tested at least once a year, and KDIGO 2024 advises checking eGFR and urine albumin at least yearly in CKD, more often as eGFR falls or albumin rises ¹.

When to worry about high creatinine

• See a doctor within days to weeks if creatinine stays above range on a rested retest, eGFR is under 60, urine shows protein or albumin, or you have diabetes or high blood pressure. NICE advises repeating the test within 2 weeks when eGFR is under 60 for the first time, to rule out acute kidney injury ⁴.
• A retest is usually enough when one value is mildly high, eGFR stays above 60, urine is clear and there is an obvious benign cause such as a hard workout, a meat-heavy dinner or creatine.

How to get a clean retest

1. 1Rest your musclesNo hard exercise or heavy lifting for 24 to 48 hours before the draw.
2. 2Skip meat beforehandNo meat for 12 hours before the blood test, as NICE advises ⁴.
3. 3Tell the clinician about creatineIf you take creatine, say so. To see your true baseline, ask whether to pause it for several weeks before the retest.
4. 4Drink normallyArrive normally hydrated; drinking extra water beforehand does not improve the result and can dilute other values.
5. 5Keep the conditions the sameUse the same lab and a similar time of day, and bring a list of every medicine, including over-the-counter painkillers.
6. 6Ask about cystatin CIf muscle or creatine is the likely reason, ask whether a cystatin C test can settle it.

How to lower creatinine, and what protects the kidneys

Removing a benign driver lowers the number without changing filtration: rehydrating, pausing creatine if a clinician agrees, eating no meat before tests, and asking the prescriber whether a secretion-blocking medicine such as trimethoprim can be swapped. These let creatinine show the true picture.

Protecting filtration, the goal that matters for health, means treating what damages the kidneys: blood pressure control, blood glucose control in diabetes, avoiding regular ibuprofen and naproxen, and not smoking. When kidney disease is present, doctors often add an ACE inhibitor, ARB or SGLT2 inhibitor, which can nudge creatinine up while slowing long-term decline ¹. Filtration lost to chronic kidney disease usually does not come back, but its decline can be slowed. The kidney panel as a whole is explained in how to read your renal panel, and every kidney page sits under the kidney topic.

Symptoms of high creatinine

High creatinine usually causes no symptoms at all. Early and moderate chronic kidney disease is silent, which is why most people with it do not know they have it. Symptoms tend to appear only in stage 4 or 5 or during sudden acute kidney injury: tiredness, swelling in the legs or around the eyes, itching, nausea, poor appetite, passing less urine and breathlessness. A blood test finds a falling eGFR years before any of these show up. If tiredness is what brought you here, the fatigue page covers its many other causes.

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