What’s A Quanti Got To Do With It?
Chapter 2 of 'From Healthy Aides to Healthier Agency'
How can a false positive delay results?
False positives are one of the drawbacks of PPDs as they can happen pretty regularly and ultimately, cost you and your agency an extra week in waiting for exams.
There are two main reasons for a false positive PPD test result:
- Individuals who received a TB vaccine called bacille Calmette-Guerin (BCG) will almost always test positive with a PPD skin test, and they will require a follow-up chest x-ray or QuantiFERON blood test for confirmation. If this is a case of an employee, it is recommended that an alternative to the PPD TB test is done to avoid unexpected false positives.
- Individuals who have latent tuberculosis will also test positive for a PPD skin test. Latent tuberculosis is not considered dangerous or contagious, but will report a positive result with the PPD Mantoux test. Just like recipients of the BCG vaccine, it is recommended that they do not receive a PPD due to the possible false positive.
[edsanimate_start entry_animation_type= “pulse” entry_delay= “0” entry_duration= “0.5” entry_timing= “linear” exit_animation_type= “tada” exit_delay= “0” exit_duration= “0.5” exit_timing= “linear” animation_repeat= “1” keep= “yes” animate_on= “scroll” scroll_offset= “75” custom_css_class= “”]
[edsanimate_end]
Those who always have a false positive PPD result can request a Tuberculosis Screening Questionnaire instead.
The PPD test also take 48-72 hours and requires at least two visits to complete. This may delay a candidate’s employment start date and cause travel inconveniences which can result in placing home care workers later than anticipated.
What is a QuantiFERON test?
A QuantiFERON is a blood assay used to test for tuberculosis. 
Alternatively, a QuantiFERON is performed in one visit and analyzed by a laboratory to rule out false positives. The tests is approved by the FDA and “contains a cocktail of three mycobacterial proteins which stimulate the patient’s T-cells in vitro to release interferon-gamma, which is then meaured using ELISA technology”.
That’s fancy medical lingo to say, the QuantiFERON is known to be incredibly reliable and prevents false positive readings as is common with PPDs.
As the CDC puts it, “The greater specificity of the Quantiferon test and the requirement for only one visit are compelling advantages.”
What are the advantages of QuantiFERON®-TB Gold In-Tube over tuberculin skin test (TST)?
- Improved specificity
- Results are not subject to reader bias
- Results are not affected by the booster phenomenon (i.e., increased sensitivity on subsequent test, leading to false-positive results)
- Accuracy is not affected by prior BCG (bacille Calmette-Guérin) vaccination
- Requires only 1 patient visit (2-4 required for TST)
- Cost savings from reduced staff time and avoidance of unnecessary follow-up testing and treatment
