From the Guidelines
The false negative rate with the Fit test is approximately less than or equal to 10%, as indicated by the ability to be qualitatively or quantitatively fit tested in a reliable way to obtain a face-seal leakage of less than or equal to 10% 1. This means that about 10% of individuals who actually have a poor fit with their respirator may incorrectly pass the fit test. When conducting respirator fit testing, it's essential to understand that no test is perfect, and this false negative rate represents the probability of the test failing to identify an inadequate respirator seal. Healthcare workers and safety professionals should be aware of this limitation and remain vigilant about proper respirator use even after passing a fit test. Some key points to consider when interpreting the false negative rate of the Fit test include:
- The test can detect only the leakage that occurs at the time of the fit testing, and the tests cannot distinguish face-seal leakage from filter leakage 1.
- The false negative rate occurs due to various factors including day-to-day variations in facial structure, changes in weight, facial hair growth, and differences in how the respirator is donned each time. To minimize risks associated with false negatives, users should perform a user seal check each time they put on a respirator, regardless of having passed a fit test, and be attentive to any sense of air leakage around the respirator edges during use. It is also crucial to note that fit tests are part of the respiratory protection program required by OSHA for all respiratory protective devices used in the workplace, and the HCW may need to be fit tested with several devices to determine which device offers the best fit 1.
From the Research
False Negative Rate with the Fit Test
The false negative rate with the Fit (Facial Seal Inspection Test) test is not directly addressed in the provided studies. However, some studies provide information on false negative rates for different types of tests:
- A study on fecal immunochemical tests (FIT) for colorectal cancer screening found that the rate of false-negative results was 66.9% 2, 3.
- The same study found that certain factors, such as younger age, use of aspirin/nonsteroidal anti-inflammatory drugs, and absence of high-grade dysplasia, were associated with false-negative results 2, 3.
- Another study on respirator fit capability test criteria for full-facepiece air-purifying respirators found that the panel passing rate (PPR) was >75% for three-, two-, and one-size families of FF-APRs at a fit factor passing level of 500 4.
- A study on the influence of facial hair length, coarseness, and areal density on seal leakage of a tight-fitting half-face respirator found that beard length and areal density negatively influenced fit factor scores, but tight-fitting half-face negative-pressure respirator fit tests can achieve adequate fit factor scores even with substantial facial hair in the face seal area 5.
Key Factors Associated with False Negative Results
Some key factors associated with false negative results include: