Diagnosis of kidney disease
How will my doctor detect kidney disease?
Since a person can have kidney disease without any symptoms, your doctor may initially detect the condition through routine blood and urine tests. Testing is the only way to know if you have chronic kidney disease (CKD).
Your doctor will use two simple tests to check for chronic kidney disease:
A urine test called ACR (Albumin to Creatinine Ratio) Healthy kidneys usually excrete very small amounts of protein in the urine. Impaired kidneys may fail to separate blood proteins from the wastes. Thus, the appearance of albumin (a kind of blood protein) in the urine is a marker of kidney damage. If this test is repeatedly “positive” for protein over a period of three months or more, it is a sign of kidney disease
A blood test to measure creatinine and estimate your GFR (glomerular filtration rate). Your GFR) is a measure of your kidney function. If your GFR is too low, it may mean your kidneys are not able to remove enough wastes and extra water from your blood. Your GFR can be estimated from a routine measurement of creatinine in your blood. Creatinine is a waste product formed by the normal breakdown of muscle cells. The amount of creatinine correlates with kidney function.
In the lab, your blood will be tested to see how many milligrams of creatinine are in one deciliter of blood (mg/dl). Creatinine levels in the blood can vary, and each laboratory has its own normal range, usually 0.7 to 1.3 mg/dl.2 If your creatinine level is only slightly above this range, you probably will not feel unwell, but the elevation is a sign that your kidneys are not working at full capacity.
However, serum creatinine values have been shown to be variable and can be affected by different parameters (e.g. diet). Equations for estimation of GFR that are based on serum creatinine have been developed in order to enable a more accurate and precise assessment of renal function. These equations are made up of the patient's creatinine values along with weight, age, and values assigned for sex and race.
Investigating the underlying cause of chronic kidney disease
Once chronic kidney disease is identified, your doctor will try to find the underlying cause of the disease. This is important, since treating the cause can help to slow the progression of chronic kidney disease. There are many different diagnostic techniques that can be used, for example imaging techniques (ultrasound, computed tomography, magnetic resonance imaging) and several different kinds of blood tests. In some cases, it may be necessary to perform a biopsy, i.e. to remove a tiny piece of the kidney to examine it under a microscope.3
- National Kidney Foundation https://www.kidney.org/atoz/content/know-your-kidney-numbers-two-simple-tests (Accessed 13.02.2019)
- MSD Manuals https://www.msdmanuals.com/professional/resources/normal-laboratory-values/normal-laboratory-values (Accessed 13.02.2019)
- Jameson, Fauci et al.: Harrison´s Principles of Internal Medicine, 20th Edition, McGraw Hill 2018