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Kidney Function Test: What It Is and Importance

Written by healthwords.ai's team of doctors and pharmacists based in UK | Updated: 29 Oct 2026 | 2 min read

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 for levels of inflammation such as a CRP or ESR blood test.

Kidney function

A kidney function blood test checks how well your kidneys are working. In the U.S., this is commonly done using a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP). These tests measure substances such as creatinine, blood urea nitrogen (BUN), and electrolytes to help assess how effectively your kidneys filter waste from your blood. Your healthcare provider may also use your creatinine level to calculate your estimated glomerular filtration rate (eGFR), an important measure of kidney function.

Why is my doctor ordering it?

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 they may need to be tested at certain intervals to ensure the medications are not causing any damage to the kidneys.

The test can monitor things associated 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.

Are there any special requirements for the blood test?

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.

Remember to press hard for a few minutes after the needle has been removed, and keep your elbow straight to prevent a nasty bruise!

This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.