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Thursday, March 28, 2013

The problem with PFTs

Pulmonary Function Testing (PFT) is a great way to assist physicians with diagnosis and monitoring patients progress, but the test doesn't come without limitations.  For one thing, the results are not diffinitive, conclusive nor diagnostic.  They are merely one of many chips in the process of differential diagnosis and monitoring. 

I believe there are a few physicians, however, who think the PFT is the fail safe test to diagnose pulmonary disease.  Yet this is not true and it cannot be true.  Surely a PFT can be a great tool to help with the process of diagnosis and treatment, but it is not fail safe, and it's definitely not diffinitive.

Consider the following limitations of the PFT:
  1. The results are based on patient effort
  2. Some practitioners misunderstand the results
  3. It is a test that is under utilized
  4. Chronic illness cannot be treated by PFT results obtained during an acute attack
So allow me to expound on all of the above. First, however, we have to describe the two basic and most important PFT tests:
  1. Forced Vital Capacity (FVC):  This is the "measurement of the patient's volume of air that they can exhale after a full inspiration with maximum speed and effort.  A normal adult has a vital capacity of 3-5 LPM.  The test basically determines how much air your chest can hold, and is determined by:
    • Configuration of the chest cage
    • Physical fitness of the patient (patients in good physical shape can inhale more air)
    • Posture of the patient (when slooped over you have less room for your lungs to expand)
    • Gender (Males can typically inhale more air than females)
    • Health of the patient (a variety of disease processes can decrease the amount of air you can inhale, such as COPD, asthma, cancer, pneumonia, scoliosis, tumors, neuromuscular disease, chest deformity, ascites, etc.
  2. Forced Expiratory Capacity (FEV1):  This is the amount of air exhaled in the first second of the FVC. It is one of the best PFT tests and cannot be faked.  However, with poor effort, can be effected.  This test can help with diagnosis:
    • 80% or better indicates normal
    • 60-79% indicates mild obstruction
    • 40-59% indicates moderate obstruction
    • 40% or less indicates severe obstruction
So while your FEV1 might look like it can diagnose obstruction, and severity of obstruction, you are completely dependent on the effort of the patinet.  If the patient generated a poor effort and this wasn't reported by the technitian, your diagnosis will be wrong. 

For example, one study showed that poor effort inversely effected FEV1, as the worse effort by the patinet the better the FEV1 looked.  The best way to see if a patinet had a good effort is to make sure the FVC loops are repeatable, and for this the physicians is at the whims of the technitian performing the test. The lazy technician may only perform one loop and say, "That's good enough."

Likewise, some practitioners do not understand that these results only fit guidelines, and are not definitive.  Some physicians don't utilize it enough, as it can be used to monitor severity of disease, and show how it is getting better with treatment.

Although, if you have a patient do the PFT during an acute attack of, say, asthma or COPD, you cannot use that as a basis for your treatment long term. I say this because if a patient is sick in the hospital with asthma, he may be so sick, able to generate so little flow, the PFT may indicate an FEV1 of 30%.  Surely this may be accurate for that patient visit, but the physician better have that patient on bronchodilators and systemic steroids to help the patient get over the crisis.  Or, in otherwords, this is a poor time to be ordering a PFT. 

If the clinitian truly wants to know how bad the patient's lungs are during the normal course of a patient's life, the PFT must be done during a normal day, not a sick day.  Unless, that is, the patient is sick every day, because then you'll have no choice. 

PFTs are also underutilized to determine effectiveness of breathing treatments.  One of the best tests to determine if albuterol works is to do a pre and post PFT, yet I find that most doctors order breathing treatments for their patients, sometimes QID, just because that patient has Cystic Fibrosis or COPD, even though the doctor has never seen any evidence those treatments work.  If the patient doesn't have reversible airway obstruction (asthma as a first or secondary condition), albuterol will not work.

Technically speaking, any patient with home nebs should have had a PFT done at some point to determine if they do any good.  Because, as we all know, 50 percent of patients receiving a placebo also said they felt the treatment made them feel better, even when it had no effect whatsoever.

  1. Frey, Michael V., "Spirometry: A Primer," February, 2013,


Anonymous said...

Glad to see you think they need to be taken in context - I've had issues with them being treated as the be all and end all! (I also hate them with a passion - they are hard work!)

What's your view on differing individual 'best predicted'? With peak flow, people can do it at home and I believe it's meant to go on personal best, which might be better or worse than best predicted (eg my actual best is a lot better than best predicted).

Obviously it's pretty hard to get an idea of someone's actual best when they can't do PFTs regularly at home, but do you think it's also a problem when someone might actually vary from the best predicted so they look ok when they're not, or worse than they really are? I once did a PFT where my FVC was well above my best predicted but FEV1 was below - still within 80% predicted but the ratio was lowered so that my doctor concluded it did show 'significant airway obstruction' (this was post-bronchodilator). My FEV1 can also be rather better than predicted when I'm doing well, but if you just went on %age predicted it wouldn't necessarily show it if I'm not doing well.

Generally, the way it works with me is that I get OK numbers before bronchodilator (if a bit weird at times because I find it harder to do in this case) but usually better than predicted after bronchodilator. Is this a way round this problem, if you think it even is a problem? (Sorry if you've said this, I can't see the post while typing. Also sorry for banging on at length...)

Loretta said...

Do you think it's possible to have an inaccurate reading due to low PFT? MY FEV1 has always been about 15% for the past 15 years. It has always remain the same. However, I definitely do not breathe the same as I did 15 years ago. Since then my health has slowly been declining but the FEV1 still remain the about same.