Variables for Quality Control

Vol. 19 • Issue 5 • Page 26

Evidence shows that quality assurance in pulmonary function laboratories is less than desirable.1-4

In a study of laboratories qualifying for a clinical trial, researchers reported a 25 percent failure of systems performing carbon monoxide diffusion testing (DLCO).3Another study reported survey results that demonstrated poor compliance with current American Thoracic Society and European Respiratory Society recommendations.5-8Only 30 percent of laboratories surveyed performed biologic quality control (BioQC) at the recommended frequency or syringe DLCO testing.

Our test results can have a profound effect on the patients we test. False positive results secondary to poor testing technique or equipment malfunction can lead to further testing, misdiagnosis of patients, or placing someone on unnecessary medication. One of my mentors used to say: “Quality is doing the right thing right all the time.” It is about time we get it right.

The Clinical and Laboratory Standards Institute’s Quality Management System Model for Healthcare can be used as a method of improving the quality of pulmonary function data.9This model uses a “path of workflow” concept where you review all aspects of testing, including processes that occur in the pretest, test, and posttest periods.


Pretest variables

The ATS/ERS guidelines give practitioners clear guidance on pretest instructions.5-8For example, communicate to patients which medications to withhold and for how long; what to avoid – large meals, smoking, alcohol consumption, etc.; and what type of clothing to wear. Assess and record any deviations from these instructions, and keep this information with the test data throughout the interpretation process. Review the subject’s medical history or administer a questionnaire prior to testing to identify critical information that may assist the technologist in test performance.

An accurate measurement of height and weight performed at the time of testing is essential. Measurements in the medical record or stated by the subject often are highly inaccurate. Estimate standing height for subjects with a spinal deformity such as kyphoscoliosis by using arm span measurement and applying the appropriate regression equation or fixed correction factor.

Certainly all instruments should meet the ATS/ERS recommendations for calibration intervals, compliance, and methodology. Equipment quality control has many nuances beyond the scope of this article; however, here are a few highlights:

• Spirometers need to be calibrated daily with a 3 L syringe and be within 3.5 percent of the target volume.

• Diffusing capacity systems need to be calibrated daily, with weekly BioQC and syringe DLCOs.

• Lung volumes (e.g., dilution and plethysmography) need to be calibrated daily with at least monthly BioQC, according to the ATS/ERS recommendations; however, in our lab, we perform lung volume BioQC weekly.

These are not optional recommendations. They must be considered as laboratory requirements on par with our arterial blood gas labs. You would never think about running an ABG analysis unless you had calibrated the instrument and run the prescribed quality control material. Quality control of PFTs must be pursued with the same diligence.

Beyond these recommendations, every piece of equipment should be enrolled in a defined preventive maintenance program. All maintenance or corrective actions should be recorded in a logbook that is kept with the instrument throughout its testing lifecycle, which is about seven years.


Test variables affecting quality

Numerous variables influence the quality of data acquired during the testing process. For example, we often forget that environment can affect the data obtained. The newer generation body plethysmographs are made of fairly thin-walled Plexiglas®. A door opening during testing or placing the box under a ventilation duct will cause pressure changes within the box. The body plethysmograph operates on Boyle’s Law, which states that pressure and volume are inversely proportional as long as temperature is constant. The technologist should allow at least one minute of tempreature equilibration time prior to maneuver performance.

The ATS/ERS guidelines define the acceptability and repeatability of the various testing modalities. It is the pulmonary function technologist’s job to meet or exceed those recommendations. Our lab reported repeatability in 18,000 adult patients of 120 mLs for FEV1and 150 mLs for FVC in spirometry testing, which influenced the ATS/ERS committee in setting their most recent repeatability recommendations.10Another factor affecting test quality is the diversity of the subjects tested, which in our lab certainly has changed over two decades. It is important to identify any language barriers so that you can communicate test expectations effectively.

Also consider the patient’s age. You may need to clarify instructions several times for young children or the elderly. In such cases, a learning needs assessment becomes an essential component of testing and not just a regulatory function. Visual aids, animated motions, or asking for an interpreter’s assistance can aid in communicating test requirements.

Well-trained personnel

The most critical factor in acquiring quality data is the testing personnel’s competency. Components of a quality laboratory personnel program should include all of the following: defined job qualifications, job descriptions, orientation and training program, competency assessment, continuing education, and performance appraisal.

The ATS-ERS committee recognized that a well-trained, motivated, and enthusiastic technologist has a direct effect on testing quality. Successful completion of the National Board for Respiratory Care’s certification or registry exam for pulmonary function technologists can demonstrate an understanding of PFTs. Earning a RPFT credential, however, does not preclude the need for continued education.


Posttest variables

A structured review of the data prior to sending it to the medical record or to the physician for interpretation should be part of the posttest process. In our laboratory, a second technologist reviews the report for errors in demographic data, quality of the test data, and maneuver selection. Not only does this process reduce the reporting error rate, but it offers an opportunity to provide constructive and positive feedback to the testing technologist.

The ATS/ERS recommendations are to report the average of at least two acceptable and repeatable maneuvers (3 units or within 10 percent of the highest), excluding outliers. Yet there are still areas of controversy that the lab needs to have a systematic process to address. At a recent national meeting, a colleague surveyed the attendees on how they would report the following acceptable DLCO data:

• Maneuver #1: 28.8 mL/min/mm Hg

• Maneuver #2: 24.8 mL/min/mm Hg

• Maneuver #3: 25.8 mL/min/mm Hg

• Maneuver #4: 23.1 mL/min/mm Hg.

Participants provided numerous scenarios on what values to report:

• Average maneuvers 1 and 3 because they are within 3 units

• Average maneuvers 2 and 3, exclude maneuver 1 as an outlier

• If maneuver 1 had the highest IVC, then average 1 and 3

• If maneuver 1 did not have the highest IVC, then average and report 2 and 3

• Average all maneuvers.

Another area that affects quality is the turnaround time of the test data. In a 2005 survey conducted by the ATS, average turnaround time reported was as follows:11

• < 1 day (15 percent)

• 1-2 days (30 percent)

• 3-4 days (27 percent)

• 5-6 days (15 percent)

• 7 days (3 percent).

Unquestionably, a turnaround time of multiple days affects the quality of the laboratory’s product as a physician waits to give the results to the patient and develop a treatment plan.

The ATS/ERS and Clinical and Laboratory Standards Institute have given us guidance and quality models to ensure that our lab results are of the highest quality and can be trusted. As pulmonary diagnostic practitioners, we need to take these recommendations and incorporate them into our everyday practice.

Visit for a list of references.


Carl D. Mottram, BA, RRT, RPFT, FAARC, is director of pulmonary function labs and rehabilitation and associate professor of medicine at Mayo Clinic College of Medicine in Rochester, Minn.

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