Diagnosing Kidney Infection

To work out if you have a kidney infection, your doctor will ask you about your symptoms and your recent medical history.
They will usually also assess your general health by taking your temperature and measuring your blood pressure.

Urine test
A urine test can help to establish whether you have a urinary tract infection (UTI). The test involves taking a small sample of urine and checking it to see if there are any bacteria in it. You’ll be given a container and told how to collect the urine, which you can do in the surgery or at home. If you do it at home, you’ll need to label the container, seal it in a plastic bag and store it in the fridge. Ideally, hand it in to the surgery within four hours.

A urine test can’t tell whether the infection – if you have one – is in your kidneys or another part of your urinary system, such as your bladder. For your GP to be confident you have a kidney infection, you need to have a positive urine test plus certain symptoms, such as a fever or a pain in your side.

Hospital scans

You may be referred to hospital for further testing if:

Your symptoms fail to respond to treatment with antibiotics
Your symptoms suddenly get worse
You have additional symptoms that aren’t usually associated with a kidney infection
You’re at risk of complications of a kidney infection

Children with recurrent UTIs will also be referred to hospital for further testing.

In these circumstances, scans can check your urinary tract for signs of problems. This may include:

A computer tomography (CT) scan – where a scanner takes a series of X-rays and a computer is used to assemble them into a detailed image of your urinary tract
An ultrasound scan – which uses sound waves to build an image of the inside of your body
An isotope scan – where a dye is injected into the bloodstream and a series of are taken

Source: NHS UK

http://www.nhs.uk/Conditions/Kidney-infection/Pages/Diagnosis.aspx