Chronic kidney disease - Diagnosing chronic kidney disease

Chronic kidney disease (CKD) is most frequently diagnosed through blood and urine tests.

Screening

If you are in a high-risk group for developing CKD, it is important to be regularly screened for the condition. People who are not in a high-risk group are not normally screened for CKD.

Annual screening is recommended for the following groups:

• people with high blood pressure (hypertension) 
• people with diabetes
• people with acute kidney injury caused by medications such as lithium or NSAIDs such as ibuprofen, kidney stones or an enlarged prostate
• people with cardiovascular disease (conditions that affect the heart, arteries and veins, such as coronary heart disease or heart failure) 
• people with a family history of stage five CKD (see below for more information about staging) or an inherited kidney disease
• people with diseases that affect several parts of the body and may affect the kidneys, such as systemic lupus erythematosus
• people with blood in the urine (haematuria) or protein in the urine (proteinuria) where there is no known cause

Your GP can advise you about whether or not you should be screened for CKD.

Most often, the diagnosis of kidney disease is made because a routine blood or urine test indicates the kidneys may not be functioning normally. If this happens, the test is usually repeated to confirm the diagnosis.

Glomerular filtration rate (GFR)

An effective way of assessing how well your kidneys are working is to calculate your glomerular filtration rate (GFR). GFR is a measurement of how many millilitres (ml) of waste fluid your kidneys can filter from the blood in a minute (measured in ml/min). A healthy pair of kidneys should be able to filter more than 90ml/min.

It is difficult to measure the GFR directly, so it is estimated using a formula. The result is called the estimated GFR or eGFR. Calculating your eGFR involves taking a blood sample and measuring the levels of a waste product called creatinine and taking into account your age, gender and ethnic group. The result is similar to the percentage of normal kidney function. For example, an eGFR of 50ml/min equates to 50% kidney function.

The following tests are used to detect proteinuria (protein in the urine)

• urine tests – used to see whether there is blood or protein in your urine
• albumin and creatinine testing – this is another urine test which compares the amounts of albumin (a protein) and creatinine in your urine. The ratio of the two (the albumin:creatinine ratio or ACR) can be used with eGFR to give doctors a more accurate idea of how the kidneys are functioning

Staging

A six-stage system, based on eGFR levels, is used to describe the progression of CKD. The higher the stage, the more severe the CKD. The six stages are described below.

• Stage one (sometimes called G1): the eGFR is normal (above 90 or more), but other testing shows evidence of kidney damage.
• Stage two (G2): the eGFR has decreased slightly (60–89), but is still considered to be in the normal range for a young adult.

If you have stage one or two CKD, it is recommended you have annual eGFR tests so the progression of the condition can be carefully monitored.

• Stage three is divided into two – stage 3a (G3a) and 3b (G3b). 
  In stage 3a, the eGFR has decreased mildly (45–59) and this is termed a mild to moderate decrease in kidney function and should be checked annually. In stage 3b (G3b) it has decreased moderately (30–44) and is termed a moderate to severe reduction in kidney function and should be checked every six months. 
• Stage four (G4): the eGFR has reduced severely (15-29). By this time, it is possible you will be experiencing symptoms of CKD. Further testing should be carried out every six months.  
• Stage five (G5): the kidneys have lost almost all of their function (an eGFR of below 15), which is known as established renal failure. Further testing should be carried out every three months.

However, over time, GFR can fluctuate, so one abnormal test result does not automatically mean you have CKD. A diagnosis of CKD is usually only confirmed if repeated eGFR tests show your eGFR is consistently lower than normal over three months. 

Other tests

A number of other tests are also used to assess the levels of damage to your kidneys. These are outlined below:

• kidney scans, such as an ultrasound scan, a magnetic resonance imaging (MRI) scan or a computerised tomography (CT) scan – used to find out whether there are any unusual blockages in your urine flow. In cases of advanced kidney disease, the kidneys are shrunken and have an uneven shape
• kidney biopsy – a small sample of kidney tissue is taken so that the cells can be examined under a microscope for damage

Want to know more?

• Advice for new kidney patients.