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How Do I Interpret My Spirometry Test?

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Updated May 29, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Question: How Do I Interpret My Spirometry Test?
A spirometry test is a type of pulmonary function test (PFT) that helps doctors diagnose the presence and severity of COPD. For many COPD patients, spirometry is one of the most misunderstood concepts of the disease. In fact, the COPD Forum is literally filled with questions about PFTs, the most frequent being "how do I interpret my spirometry test"?
Answer: Because spirometry test results are always compared to normal, predicted values, the first thing to understand when interpreting spirometry is what's considered normal.

Normal predicted values are obtained during population-based research studies of people with normal lung function. Once you take the test, your results will be compared to normal predicted values acquired from someone of the same age, height, weight, sex and ethnicity. In general, normal results reflect an FVC and FEV1 above 80% predicted, and an FEV1/FVC ratio of greater than 0.70 (70 percent).

5-Step Approach to Spirometry Interpretation

Once you've had a spirometry test, the technician will send your results to your primary care provider. Your primary care provider will interpret your test using a systematic approach. There are several methods available to assist clinicians with this process; the one your doctor chooses to use is a matter of personal preference. The following 5-step process is one of the easiest to understand:

  • Step 1: Begin by looking at the forced vital capacity (FVC) to determine if it's within a normal range.
  • Step 2: Next, look at the forced expiratory volume in one second (FEV1) to see if it's within normal limits.
  • Step 3: If the FVC and the FEV1 are both normal, stop at this step—the spirometry test is normal.
  • Step 4: If the FVC and/or the FEV1 are decreased, there is a strong possibility of lung disease and you should go on to Step 5.
  • Step 5: If Step 4 suggests the presence of lung disease, look closely at the %predicted for FEV1/FVC. If %predicted for FEV1/FVC is 69% or less (restrictive lung disease.

At your follow-up appointment, your provider should review your test results with you in detail and give you a chance to ask questions. Before you leave the office, ask your doctor for a copy of your test results so you'll have something to reflect on when you get home, and something to compare to your last test or any tests you may have in the future.

What Do the Results Mean?

Not only do your spirometry results confirm a diagnosis of COPD, they also tell your doctor the degree of lung damage present in your lungs--a process known as "grading" or "staging." There are four grades (stages) of COPD: Gold I, Mild COPD; Gold II, Moderate COPD; Gold III, Severe COPD; Gold IV, Very Severe COPD. Read more about the GOLD Grading System to find out what stage of COPD you're in.

COPD treatment guidelines are optimized for every stage of COPD. Once your doctor determines the severity of your COPD, she can then recommended the most effective treatment.

How Can I Improve My Spirometry Results?

The single most effective way to slow the progression of lung function decline in COPD is to quit smoking. For more tips on how to prevent COPD from becoming worse, read:

How To Keep COPD From Worsening

NOTE: The step-by-step approach to spirometry interpretation included in this article should only be used as a guideline. It is not meant to diagnose lung disease or replace talking to your doctor. It's also important to point out that in some cases, these guidelines won't always apply, especially if your numbers overlap or test results are unusual. That's why the best person to talk to about your spirometry numbers is your doctor.

Spirometry for Heath Care Providers. Global Initiative for Obstructive Lung Disease. Updated June 2010.

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