Mayo Clinic: Test can help diagnose asthma; antibiotics usually not needed to treat abscess

DEAR MAYO CLINIC: I've had a cough and some wheezing that won't go away. My doctor suspects asthma and ordered an exhaled nitric oxide test. Can you tell me more about this test?

ANSWER: Asthma is usually diagnosed based on symptoms, a physical exam and certain tests — such as peak flow measurement and spirometry tests — to see how well your lungs are working. But sometimes the diagnosis is still uncertain. To gather more clues, your doctor may use an exhaled nitric oxide test. This simple test takes only a few minutes and can be performed in your doctor's office or in a lung function laboratory.

Asthma causes a particular inflammation of airways in the lungs. Studies have shown that an elevated exhaled nitric oxide — a gas that's expelled when you breathe out — can be a reliable marker for asthma airway inflammation in certain patients.

Nitric oxide is produced throughout your body, including your lungs, to fight inflammation and relax constricted muscles. If your airways are inflamed, as often occurs with asthma, your body may increase its production of nitric oxide. Generally, the higher the level of exhaled nitric oxide, the greater the inflammation in the airways.

To do the test, you breathe into a mouthpiece attached with a tube to an electronic device. As you breathe out steadily, the device measures the level of nitric oxide exhaled. To make sure results are accurate, your doctor may ask you to avoid certain activities — such as eating, drinking, smoking and exercising — a few hours before the test. The test can be used to diagnose asthma as well as fine-tune and maintain asthma control, but your doctor will need to sort out other possible factors that can also increase nitric oxide levels unrelated to asthma.

If your nitric oxide levels are very high, your doctor may prescribe a steroid or other medications to decrease airway inflammation. Checking your levels again at a later date can help determine how treatment is working. (adapted from Mayo Clinic Health Letter) — Dr. Clayton T. Cowl, pulmonary and critical care medicine, Mayo Clinic, Rochester, Minn.

DEAR MAYO CLINIC: I recently had an abscess on my leg. My doctor drained it but didn't prescribe any antibiotics. Was that an oversight?

ANSWER: Probably not. Treatment for a skin abscess — a pus-filled bump that develops under the skin — usually involves your doctor piercing it with the tip of a scalpel after applying a local anesthetic. After the pus drains out, often the abscess is rinsed out with saline solution and loosely packed with gauze.

If you're in good health and have no other problems related to the abscess, your doctor may not prescribe any antibiotics. Antibiotics aren't particularly helpful in treating uncomplicated abscesses. One study compared a group that was prescribed an antibiotic after abscess incision and drainage with a group that was prescribed a sugar pill (placebo). The study found no difference in healing between the two. Other studies have come to similar conclusions. In addition, antibiotics can cause side effects and some are expensive.

Another concern is that overprescribing antibiotics might promote resistance among different strains of bacteria. Germs that are resistant to antibiotics are much harder to treat and can mean longer-lasting illnesses, more doctor visits or extended hospital stays and the need for more expensive and toxic medications. Some resistant infections can even cause death.

An example of the dangers of antibiotic resistance is the spread of methicillin-resistant Staphylococcus aureus (MRSA). MRSA was once a concern only for people in the hospital, but a newer form of MRSA is causing infections in healthy people (community-acquired MRSA), and it predominately causes skin abscesses.

Wise use of antibiotics is important for preventing the spread of MRSA. But even if you have an MRSA abscess, as long as there isn't more than an inch or so of redness surrounding the abscess — suggesting a skin infection called cellulitis — antibiotics aren't necessary. (adapted from Mayo Clinic Health Letter) — Dr. Stephen Merry, family medicine, Mayo Clinic, Rochester, Minn.

The MAYO CLINIC Q&A is an educational resource and doesn't replace regular medical care. Email questions to MayoClinicQ&A@mayo.edu. For more information, visit mayoclinic.org.

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