Kidney values

and Eva Rudolf-Müller, doctor

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

More about the experts All content is checked by medical journalists.

Kidney values are laboratory values that show how well the kidneys are working. They are determined in the blood or in the urine. Important kidney values are, for example, creatinine, urea and uric acid. If they deviate from the normal value, this can indicate kidney disease. Here you can read everything you need to know about kidney values, which normal values apply and which diseases change the values.

What are kidney values?

The kidney values are laboratory parameters that allow conclusions to be drawn about kidney function. The doctor very often determines the following kidney values:

Creatinine
Creatinine or inulin clearance
Cystatin C.
urea
uric acid

Other blood tests that can help determine how well your kidneys are working include electrolytes, phosphate, and blood gases. The following are also determined in the urine:

PH value
Egg white (protein)
blood
Ketones
Sugar (glucose)
Leukocytes
nitrite

Creatinine and Inulin Clearance

The clearance indicates how quickly the kidneys filter certain substances out of the blood. For the calculation, the doctor can use either creatinine (breakdown product of creatine) or inulin (a multiple sugar). The latter, however, is very susceptible to disruptive factors and is therefore usually no longer determined.

Urea and uric acid

Urea is the end product of protein metabolism. Every day, about 20 to 40 grams of urea are produced in the liver from ammonia and carbon dioxide (CO2). In addition to small amounts that are given off with sweat and stool, most of the urea leaves the body via the kidneys, where the urea is filtered out of the blood. Part of it is then reabsorbed (i.e. returned to the blood), while the rest is excreted with the urine. How much urea is reabsorbed depends on the kidney blood flow and the amount of urine: the less urine is excreted, the more urea is transported back into the blood.

Uric acid is a breakdown product of building blocks of the genetic information DNA (deoxyribonucleic acid), more precisely the purine bases adenine and guanine.

When do you determine the kidney values?

The doctor will measure the kidney values in the blood and urine to diagnose kidney disease or to check its progress. The urea value is also used to control protein intake in patients with known kidney weakness (renal insufficiency).

Kidney values are not only used to assess kidney function. Uric acid, for example, also plays an important role in the diagnosis and therapy control of hyperuricemia (gout). It is also measured repeatedly during chemotherapy or radiation therapy. The doctor also determines the creatinine value in the context of high blood pressure, metabolic and connective tissue diseases.

When are the kidney values too low?

The clearance of the substances inulin or creatinine provides information about the filtration performance of the kidneys. So it falls when kidney function is impaired (acute or chronic kidney failure). To a lesser extent, creatinine clearance also naturally decreases with increasing age.

A lowered creatinine level in the blood has no meaning. It is only found as a secondary finding in patients with underweight or low muscle mass.

A reduced protein intake also lowers the urea level. Congenital enzyme defects are more rarely the reason for lowered urea levels.

The most common cause of low uric acid levels is an overdose of medication designed to lower uric acid levels. These are used to treat gout.

Kidney values: table with lower limit values

	men	women
Creatinine (in serum)	<50 years: 0.84 - 1.25 mg / dl > 50 years: 0.81 - 1.44 mg / dl	0.66 - 1.09 mg / dl
Creatinine (in urine)	1.5 - 2.5 g / 24 hours	1.0 g / 24 hours
Cystatin C	0.5-0.96 mg / l	0.57-0.96 mg / l
urea	<50 years: 19 - 44 mg / dl > 50 years: 18 - 55 mg / dl	<50 years: 15 - 40 mg / dl > 50 years: 21 - 43 mg / dl
Uric acid (in serum)	3.4 - 7.0 mg / dl	2.4-5.7 mg / dl

When are the kidney values too high?

The measured values of the individual kidney values respond differently to different diseases. Reasons for an increased creatinine level are for example:

High blood pressure caused by narrowing of the kidney vessels (renovascular hypertension)
Acromegaly (hormonal disease with enlarged hands, feet, ears, nose, etc.)
acute kidney failure (e.g. due to allergic reactions, toxins, occlusion of the kidney vessels, multiple myeloma or disintegration of erythrocytes or muscle cells)
chronic kidney failure (e.g. due to diabetes mellitus or connective tissue diseases)

If the concentration of uric acid is increased, the doctor calls this hyperuricemia. It is either due to a congenital metabolic disorder or manifests itself as a symptom in:

Fast
poorly controlled diabetes mellitus
high fat diet
Underactive thyroid or parathyroid
Poisoning (e.g. with lead)

Increases in urea are also found in the event of a loss of function of the kidneys, which can result from reduced kidney blood flow, certain medications or urinary flow disorders, among other things. A slight increase in the urea level occurs with a protein-rich diet or low fluid intake (dehydration).

Increased kidney values are also found in severe general infections such as measles.

Kidney values: table with upper limit values

	men	women
Creatinine (in serum)	<50 years: 1.25mg / dl > 50 years: 1.44 mg / dl	0.96 mg / dl
Creatinine (in urine)	2.5 g / 24 hours	1.3 g / 24 hours
Cystatin C.	0.96 mg / l
urea	<50 years: 44 mg / dl > 50 years: 55 mg / dl	<50 years: 40 mg / dl > 50 years: 43 mg / dl
Uric acid (in serum)	7.0 mg / dl	5.7 mg / dl
Uric acid (around urine)	With a normal diet 800 mg / day (24 hours)

What to do if the kidney values change?

If the kidney values are increased, the doctor must first and foremost rule out kidney disease. Urine tests already provide a lot of important information for this. Among other things, they show whether protein or blood is being lost through the kidneys. The kidney specialist (nephrologist) can also assess the urine through a microscope.

An ultrasound examination of the kidney can also provide information about pathological changes - such as the structure or size of the kidneys or the urinary tract. Sometimes it is also helpful to obtain a tissue sample from the kidney, which is stained in the laboratory and examined under a microscope. The tissue sample is taken with a long needle, which the doctor pierces through the skin under the guidance of ultrasound.

Apart from various types of kidney damage, other diseases can also change kidney values.The doctor must also consider these options in conjunction with the patient's complaints and carry out further examinations accordingly.

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