Blood tests have many different uses. Some of these include being used to diagnose a condition, to monitor a particular organ in the body such as the kidney or liver, and they can also be used to give measurements of bodily processes such as sugar levels in the blood or current levels of inflammation.
The kidney function blood test is also known as urea and electrolytes, or U & E (doctors pronounce this "U's and E's"). It is one of the most commonly requested tests, and provides information on how the kidneys are functioning. It gives different markers of how well the kidneys are coping at filtering out waste products and also gives levels of some waste products.
This would be a normal test to order when doing some routine blood tests. Specifically, it will give your doctor information on how your kidneys are functioning at that point in time. Your kidneys are involved in processing many medications, and so it may need to be tested at certain intervals to ensure the medications are not causing any signs of damage to the kidneys. It can monitor things with a sudden illness, such as dehydration or sepsis that can put temporary stress on the kidneys - called acute kidney injury. It can also monitor kidney function if your kidneys have started to deteriorate with age or alongside other medical conditions, called chronic kidney disease.
You do not need to be fasting for this blood test, there are no special requirements. It can be taken like any normal blood test and is usually taken in a gold or yellow colour bottle. Remember to press hard for a good few minutes after the needle has been removed and keep your elbow straight, to prevent a nasty bruise!