Tests and diagnosis

By Mayo Clinic Staff

Your doctor may order lab work or imaging scans to help determine what's causing your symptoms.

Laboratory tests

Many infectious diseases have similar signs and symptoms. Samples of your body fluids can sometimes reveal evidence of the particular microbe that's causing your illness. This helps your doctor tailor your treatment.

  • Blood tests. A technician obtains a sample of your blood by inserting a needle into a vein in your arm or hand. This test may be slightly uncomfortable for some people but usually takes only a few minutes.
  • Urine tests. This painless test requires you to urinate into a container. To avoid potential contamination of the sample, you may be instructed to cleanse your genital area with an antiseptic pad and to collect the urine midstream.
  • Throat swabs. Samples from your throat, or other moist areas of your body, often are obtained with a sterile swab.
  • Spinal tap (lumbar puncture). This procedure obtains a sample of your cerebrospinal fluid through a needle carefully inserted between the bones of your lower spine. In most cases, you'll be asked to lie on your side with your knees pulled up toward your chest. This test can be uncomfortable and you might develop a headache afterward.

Imaging scans

Imaging procedures — such as X-rays, computerized tomography and magnetic resonance imaging — can help pinpoint diagnoses and rule out other conditions that may be causing your symptoms.

  • X-rays. This painless procedure exposes a part of your body to a small dose of radiation to produce an image of the structures inside your body. A chest X-ray, for example, can reveal signs of pneumonia.
  • Computerized tomography (CT). CT scans digitally combine X-rays taken from many different angles to produce cross-sectional images of bones, organs and other soft tissues. CT images reveal more details than do regular X-rays.
  • Magnetic resonance imaging (MRI). MRI uses radio waves and a strong magnetic field to produce detailed images of internal structures. This test involves lying on a narrow table that slides into a tunnel within the MRI machine. Some people find the enclosed space claustrophobic, but medications can help you relax and can make the MRI experience easier.


During a biopsy, a tiny sample of tissue is taken from an internal organ for testing. For example, a biopsy of lung tissue can be checked for a variety of fungi that can cause a type of pneumonia.

Jan. 23, 2013