Kidneys and electrolytes · Blood

Creatinine

A waste product from the muscles that the kidneys filter from the blood; the basis for calculating kidney function (eGFR).

At a glance

Measured in blood
In 17 test panels
No special preparation

Explanation

Creatinine: what is measured?

Creatinine is a waste product formed by the normal breakdown of creatine in the muscles. The body makes a fairly constant amount of it each day, depending on muscle mass. The kidneys filter creatinine from the blood and excrete it in the urine. If the kidneys work less well, more creatinine stays behind in the blood and the value rises. Because the amount also depends on muscle mass, age and sex, the laboratory converts creatinine into the eGFR, an estimate of the kidneys' filtration rate.

What can it detect?

Reduced kidney function, acute or chronic
Reduced blood flow to the kidneys, for example with dehydration or heart failure
Monitoring of the kidneys in diabetes, high blood pressure and with medicines that put a strain on the kidneys

Result

What does the result mean?

Creatinine too high

A raised creatinine usually means the kidneys are filtering less. With a slightly raised value, harmless factors often play a role: a lot of muscle mass (strength training), creatine supplements, a large portion of cooked meat in the hours before the sample collection, dehydration or heavy exercise. Some medicines also raise creatinine without the kidneys working less well, including trimethoprim and cimetidine. A persistently raised value fits chronic kidney damage, usually due to diabetes, high blood pressure or vascular damage, or a blocked urine flow (prostate, kidney stones). Kidney damage causes no symptoms for a long time; only with severe damage do tiredness, itching, nausea, fluid in the legs and passing less urine develop. A sudden sharp rise may point to acute kidney damage, for example due to dehydration combined with water pills (diuretics), anti-inflammatory painkillers (NSAIDs) or blood pressure medication.

Creatinine too low

A low creatinine is usually no reason for concern. The value is low with little muscle mass (older people, people who have been bedridden for a long time, people with an amputation or muscle disease), during pregnancy and with malnutrition. In those situations the calculated eGFR overestimates the true kidney function.

After an abnormal result

The GP assesses the eGFR that goes with the creatinine and, after a first abnormal result, repeats the measurement within 3 months, or within a few days to a week with a strongly abnormal value. The urine is also tested for albumin (albumin-creatinine ratio), and blood pressure, glucose and cholesterol are measured. With a strongly reduced kidney function, a lot of protein in the urine or a rapid decline, the GP refers to an internist-nephrologist.

Reliability

How reliable is the test?

Creatinine on its own is a rough measure: the value can still be within the reference values while kidney function has already dropped considerably, and a slight rise means something different in someone with a lot of muscle than in a slight older person. That is why, according to the Dutch GP guideline (NHG), the GP mainly assesses the eGFR, which is calculated from creatinine, and confirms an abnormal value with a repeat measurement. The measurement itself is well standardized in Dutch laboratories: according to the Dutch medical specialists' guideline (FMS), a difference of 15 percent or more between two measurements is a real difference.

What can affect the result?

Creatine supplements, a lot of muscle mass and a meat meal shortly before the sample collection raise creatinine without the kidneys working less well; little muscle mass lowers it.
Dehydration, heavy exercise and some medicines (including trimethoprim, cimetidine, NSAIDs) raise the value temporarily.
A single measurement says nothing about the course over time; chronic kidney damage is only diagnosed if the abnormality is still present after 3 months.
Creatinine responds slowly: in acute kidney damage the value only rises after 1 to 2 days.

Who it is for

Who is the test useful for?

Useful for

Useful with diabetes, high blood pressure, cardiovascular disease or kidney disease in the family, with the use of medicines that put a strain on the kidneys or are excreted by the kidneys (including metformin, blood pressure medication, NSAIDs, lithium), in strength athletes who use creatine or anabolic steroids, and to monitor a previously abnormal value. In healthy adults without risk factors, the chance of an abnormality is small; a slightly raised value is then more often caused by a lot of muscle mass, creatine or a meat meal than by kidney damage.

How common is it?

Chronic kidney damage affects about 1 in 10 adults in the Netherlands and is much more common at older ages; in about 5 in 100 Dutch people it is recorded in the GP's records. Most have no symptoms and do not know it. Diabetes and high blood pressure are the main causes.

NHG guideline on chronic kidney damage; NIVEL primary care registrations (2021)

Drawbacks and risks

In strength athletes and creatine users, creatinine is often slightly raised without kidney damage; this regularly leads to unjustified worry about the kidneys.
With little muscle mass, a normal value can hide reduced kidney function.

Get tested

Creatinine: test panels

Creatinine is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.

Blood draw
BUN (Urea Nitrogen) and Creatinine
BUN and creatinine; renal function.
€ 26,00
Blood draw
Bodybuilder Test
Panel for strength and muscle development; hormones, liver, and muscles.
€ 134,00
Blood draw
General Health Checkup
With this General Health Check-up, you gain detailed insight into your overall health and well-being.
€ 125,00
Fingerstick
Creatinine
Measure your kidney function at home with creatinine finger prick including eGFR and CKD-EPI calculation.
€ 17,00
Blood draw
Creatinine
Measure your kidney function with creatinine including eGFR and CKD-EPI calculation.
€ 17,00
Blood draw
PhenoAge
PhenoAge Biological Age Test; determine your biological age with 9 standard blood values.
€ 85,00
Blood draw
Hormones Male
Total testosterone, free testosterone, SHBG, creatinine, and eGFR. For men with hypogonadism, low libido, or during strength training.
€ 125,00
Blood draw
Endurance Sports
Complete blood count, iron status (ferritin, transferrin), kidney function, liver function, testosterone, and hs-CRP. For athletes and endurance sport participants.
€ 203,00
Blood draw
General Blood Test (Basic)
Hemoglobin, MCV, TSH, fT4, eGFR, creatinine, ALT, AST, sodium, and potassium. General health check of kidney, liver, and thyroid.
€ 125,00

How reliable is the test?

Creatinine