Blood draw
Cystatin C
Cystatin C; an additional marker of kidney filtration.
€ 69,00
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Kidneys and electrolytes · Blood
Cystatin C
A kidney function measure alongside creatinine; less dependent on muscle mass, so useful when creatinine leaves doubt.
At a glance
- Measured in blood
- In 2 test panels
- No special preparation
Explanation
Cystatin C: what is measured?
Cystatin C is a small protein that almost all cells make at a fairly constant rate. The kidneys filter it from the blood. If the kidneys work less well, cystatin C rises. Unlike creatinine, which comes from muscle tissue, cystatin C hardly depends on muscle mass and meat consumption. From the value, alone or together with creatinine, the laboratory can calculate an estimated kidney function (eGFR).
What can it detect?
- Reduced kidney function, also in people in whom creatinine gives a distorted picture, such as with a lot of or little muscle mass
- Confirming or ruling out a slightly low eGFR based on creatinine
Result
What does the result mean?
Cystatin C too high
A raised cystatin C fits reduced kidney function: the kidneys then filter it out less well. Reduced kidney function causes no symptoms for a long time. Cystatin C can also rise without a kidney problem, for example with an overactive thyroid, with the use of corticosteroids such as prednisone, with smoking, with overweight and with inflammation. Rarely, a raised value goes together with a rheumatic disease or a malignant condition.
Cystatin C too low
A low value fits good kidney function and has no further meaning. An underactive thyroid can also lower the value without anything being wrong with the kidneys. A low value causes no symptoms.
After an abnormal result
With a raised value, the GP repeats the kidney function test and has albumin in the urine measured. If the abnormality lasts longer than three months, the approach of the Dutch GP guideline (NHG) on chronic kidney damage follows, with attention to blood pressure, medicines and the risk of cardiovascular disease; with a strongly reduced or rapidly declining kidney function, referral to an internist or nephrologist follows.
Reliability
How reliable is the test?
Cystatin C is a reliable kidney function measure that is less affected by muscle mass, age and diet than creatinine. According to the guideline on chronic kidney damage, an estimate based on cystatin C, or on creatinine and cystatin C together, is preferred with a creatinine-based eGFR between 45 and 60 without other signs of kidney damage, diabetes or high blood pressure, if the diagnosis has consequences. The Dutch GP guideline (NHG) on chronic kidney damage bases the classification on the eGFR and albumin in the urine. The measurement method strongly determines the result, which is why reference values differ by laboratory.
What can affect the result?
- Thyroid disorders, corticosteroids such as prednisone, smoking, overweight and inflammation affect the value without kidney function changing.
- The result differs by measurement method; preferably compare consecutive results from the same laboratory.
- One abnormal value is not a diagnosis: according to the NHG guideline, chronic kidney damage requires an abnormality that lasts at least three months.
- An acute illness or dehydration can temporarily lower kidney function.
Who it is for
Who is the test useful for?
Useful for
The result says the most with a slightly low creatinine-based eGFR where there is doubt, and in people in whom creatinine gives a distorted picture: a lot of or very little muscle mass, malnutrition, an amputation, a vegetarian diet or the use of creatine. Kidney function can also be monitored in diabetes, high blood pressure or cardiovascular disease. In people without symptoms or risk factors, an abnormality is often a mild or temporary decrease.
How common is it?
Chronic kidney damage is common, especially at older ages: among people over 65, more than 1 in 5 have an eGFR below 60. It is often a mild, stable decrease without symptoms. How often cystatin C is abnormal in people without known kidney damage is not recorded separately.
NHG guideline on chronic kidney damage; the figure for people over 65 is an estimate
Drawbacks and risks
- A slight rise due to the thyroid, prednisone, smoking or inflammation can wrongly be read as kidney damage.
- A mild, stable decrease in kidney function at an older age can cause unnecessary worry.
Evidence
Sources
This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.
More about risks and results- NHG-Standaard Chronische nierschade (M109)
- FMS Richtlijnendatabase, richtlijn Chronische nierschade: Bepaling van nierfunctie en albuminurie
- FMS Richtlijnendatabase, richtlijn Chronische nierschade: Samenwerking met laboratoriumspecialisten klinische chemie
- NVKC, allesovertesten.nl: Cystatine C
- Thuisarts.nl: Ik heb nierschade
More explanations
Other tests: Kidneys and electrolytes
- BUN/creatinine ratio
- Chloride
- CO2 (bicarbonate)
- Creatinine
- Creatinine (urine)
- eGFR
- Phosphate (inorganic)
- Potassium
- Sodium
- Urea
- Urea nitrogen (BUN)