What do kidney blood tests do?
The kidney’s main function is to excrete waste from your body, so if your kidneys aren’t working properly, there are likely to be higher than normal levels of waste products in your blood. Kidney blood tests therefore look at the blood levels of these waste products to see how well your kidneys are performing their excretion function.
How is the kidney blood test done?
Usually your doctor will ask you not to eat excessive amounts of meat or other protein for 24 hours before a kidney blood test. During the test your doctor will extract blood from your veins into a tube, which will then be sent off for testing at a laboratory. Test results are usually available within a few days, or even on the same day if you’re having the test in a hospital.
What do kidney blood tests look for?
A kidney blood test measures the levels of different substances in the blood:
Blood Urea Nitrogen (BUN) Test
This type of kidney blood test looks at the nitrogen levels in your blood, which is an indicator of urea levels. When your body digests proteins, urea is the waste product that is produced by your liver. In a normal healthy body, your kidneys filter this urea out of your blood and excrete it through your urine. If your kidneys aren’t working correctly they won’t be able to filter this urea properly and so the levels of nitrogen in your blood will be elevated.
When your body metabolises energy in muscles, the waste product creatinine is produced. In a normal, healthy body, creatinine is absorbed by the kidneys and then excreted through your urine. However, when your kidneys aren’t functioning properly, this filter system isn’t as efficient, and so your blood will contain higher than normal amounts of creatinine. Normally, creatinine levels in the blood tend to be very stable. This is because the amount produced depends on your muscle mass, which typically doesn’t fluctuate very much. This type of kidney blood test can therefore be a more sensitive indicator of kidney problems than a BUN test.
Other kidney blood tests
Kidney blood tests can also measure the blood levels of other chemicals that are regulated by your kidneys, such as sodium, calcium, magnesium, phosphorus, uric acid and glucose. Any abnormal levels of these substances need further investigation.