Patients at risk should have their kidney function checked regularly. But even supposedly healthy people can benefit from a regular health check-up by a doctor. In some European countries, health services provide a health check. These check-ups are usually done by general practitioners and are, in some countries, restricted to patients who have risk factors, such as higher age, high blood pressure, the presence of diabetes mellitus and/or cardiovascular disorders.
How do you recognise when your kidneys are not working optimally?
Blood test
In kidney disease, the kidneys can no longer filter the blood adequately and waste products remain in the body. Creatinine and urea accumulate in the blood. The levels of these metabolic end products can be determined with a blood test. Since creatinine is formed in the muscles, the amount of creatinine in the blood depends on muscle mass and muscle work. The normal value is 0.8 – 1.2 mg/dl or 70 – 106 µmol/l, and the normal urea concentration is 20 – 45 mg/dl or 3.3 – 7.5 mmol/l.
Higher levels of creatinine in the blood denote poor levels of kidney function.
Glomerular Filtration Rate (GFR)
The glomerular filtration rate (GFR) can be used to assess the kidney function and the severity of the disease. The GFR is the volume filtered by the glomeruli of the kidneys in a given time. The normal value is 90 to 130 millilitres per minute. Thus, a healthy kidney filters at least 90 millilitres of primary urine from the blood per minute. The GFR measure most commonly used in clinical practice is estimated using the creatinine level in the blood serum and taking into account age and gender.
Chronic kidney disease can be staged, according to the estimated glomerular filtration rate (eGFR). It is an important marker to decide on diagnosis, prognosis and treatment.
Patients with stage 5 CKD have an eGFR of less than 15 millilitres per minute and may be dependent on dialysis, filtering the toxins from the blood artificially, or a kidney transplant.
In addition, a sensitive marker for determining the GFR is the level of the metabolic protein cystatin C in serum, which is independent of muscle mass and therefore of age and sex. In declining kidney function, cystatin C is insufficiently filtered out of the blood. The normal value is below 0.96 milligrams/litre.
Urine test
In addition to blood values, urine values are also important for examining kidney function. If the filtering capacity of the glomeruli is impaired, protein may no longer be retained in the body and passes increasingly into the urine (proteinuria).
A healthy person normally excretes little or no protein, at most 200 milligrams of protein per day.
To assess kidney function, the concentration of the protein albumin in the urine should be checked; in a healthy person, it is less than 30 milligrams. A concentration of 30-300 milligrams of albumin is called microalbuminuria. A rapid urine test – urinalysis or urine dipstick testing – for microalbuminuria can provide a first indication of an issue with the kidneys. However, the protein concentration in the urine depends on your fluid uptake. To increase the accuracy of the test, the albumin concentration is therefore related to the concentration of creatinine in the urine in a laboratory test (albumin/creatinine quotient). Diabetics in particular should be tested regularly for microalbuminuria to assess the filtering capacity of the kidneys.
If protein is detected in a rapid urine test, further tests must be undertaken.
Urine dipstick testing is an essential part of check-ups by the general practitioner. It provides quick and easy information about the protein concentration and thus about the health of the kidneys. The less protein in the urine, the healthier the kidneys.
Stages of CKD according to KDIGO 2012 Clinical Practice Guideline
