Kidney function blood test

A kidney function blood test can identify how well your kidneys are working. You may be advised to have a blood test for your kidney function if your doctor or GP believes that there is a possible problem with one or both of your kidneys. In other cases, a problem with kidney function may be picked up incidentally by a blood test for another reason.

This blood test can also be used for people who are going through treatments, such as chemotherapy, to help to assess the continual good functioning of the kidneys during the treatment.

The blood test will only take a few minutes and can usually be performed at your local hospital or GP surgery. It is likely that the blood will be taken from the skin on the inside of your elbow joint or the back of your hand. Once this has been completed the blood will be sent to the lab to be tested for the level of urea, creatinine and electrolytes.

Creatinine/eGFR

Creatinine is a waste product of muscle metabolism and is the usual blood test used to assess kidney function. If there is a high level in your blood it may indicate that your kidneys are not functioning well. When testing for creatinine your doctor may look at your BMI, as people with more muscle may naturally have a higher level in their blood. Compared to testing urea level, this can give a more accurate indication of the level of kidney function. An eGFR (estimated Glomerular Filtration Rate) is a more detailed assessment of your kidney function and it is calculated from your blood creatinine level.

Electrolytes

The electrolytes measured in kidney blood tests are usually sodium, potassium, chloride and bicarbonate. If the electrolyte levels in your blood are abnormal it can indicate that there is kidney function problem.

Urea

Urea is the waste product that is made when protein is broken down. If the kidneys are functioning well this should be at a low level, so a high level may indicate that the kidney is not working properly or you are severely dehydrated.