A kidney function blood test usually measures the level of the waste product creatinine and certain dissolved salts (electrolytes) in your blood. The test is done to check for a number of aspects of kidney function.
- Creatinine is a waste product in your body that is made by your muscles. It passes into your bloodstream, and is usually passed out in your urine (pee). A high level of creatinine in your blood indicates that your kidneys may not be working properly.
- Dissolved salts that are routinely measured are sodium, potassium, chloride and bicarbonate. They are sometimes referred to as ‘electrolytes’. Abnormal blood levels of any of these may sometimes be due to a kidney problem.
- eGFR stands for estimated glomerular filtration rate. Although the level of creatinine in your blood is a useful guide to kidney function, the eGFR is a more accurate measure of how well your kidneys are filtering your blood. Using your blood creatinine, and your age and sex, your eGFR can be calculated by computer and reported with the creatinine blood test.
In some cases urea and uric acid are also tested which are other waste products.
- Urea is produced when protein is broken down by your body. Healthy kidneys get rid of more than 90% of the urea your body produces. A high level of urea in your blood may indicate that you are dehydrated, bleeding in your bowel, or that your kidneys may not be working properly.
- Uric acid is produced when purines are broken down. High uric acid is a risk factor for gout. This is usually measured when helping to diagnose gout and monitoring the response to treatment of gout.
A urine test is sometimes done to check for excess protein leaking from your urine. Albumin is a type of protein and a high ratio indicates that your kidneys are leaking protein. This can be elevated in certain conditions such as kidney damage from diabetes mellitus and pre-eclampsia in pregnancy.