For many years, the best way to determine if someone may have an active tuberculosis infection was to use a skin test. The tuberculin skin test [TST] is implanted just under the skin and then sits for a predetermined amount of time. The reaction to the TST is then judged by the care provider to determine if the result is positive, negative, or inconclusive. The QuantiFERON-TB Gold blood test takes some of the guesswork out of the tuberculosis screening process.
TB, when it isn’t treated right away, can become a fatal disease. Even when it isn’t fatal, tuberculosis can cause a lung infection, spread to the kidneys, and even affect the brain. Spread through droplets that come from the respiratory system, like with a sneeze, it can be spread from person to person quite easily. A definitive screening test is needed for certain professions because of close human contact and that’s what this blood test can provide.
What Are the Advantages of the QuantiFERON-TB Gold Blood Test?
This blood test can measure active and latent TB infections, but only in adult patients. The TST is still considered the standard for children. Only one visit is required for this blood test instead of multiple visits with the TST, which saves everyone time and money.
There are some additional advantages that this blood test has over the TST as well.
Instead of needing to visually judge a skin test, there is a set of baseline markers that test results can be compared against universally to determine if a TB infection is present.
There is less bias.
Because the results of the blood test are measured universally, there is no local bias present in reading the results.
It can’t be boosted.
The TST will eventually become an inaccurate measurement of a TB infection because of what is known as the “booster” effect. After several skin tests, it is common for false positives to be read. The QuantiFERON-TB Gold blood test eliminates this effect completely.
It is accurate.
Individuals who have received a BCG vaccination in the recent past will not receive accurate TST results. This blood test eliminates the inconvenience.
Although the accuracy of this blood test is often better than the TST, it is not appropriate for some individuals. Be sure to speak with your doctor about this TB test and if it could be right for you.
Who Should Not Take the QuantiFERON-TB Gold Blood Test?
Besides children, there are certain population groups that are not considered viable candidates for taking this blood test. Anyone who has an altered immune function fits into this category. This may be the result of an autoimmune disorder, an HIV infection, or people who are receiving immunosuppresive medications.
Certain clinical conditions may also alter the effectiveness of the results. This includes people who have a confirmed diagnosis of diabetes, renal failure, certain cancers and blood disorders, and silicosis.
Women who are pregnant are also not considered good candidates for this blood test.
The CDC, however, has approved the use of this blood test as a screening tool for virtually all individuals based on current data, even if the results from the test have not been studied. This is why it is important to speak with your provider about this specific blood test to see if it would be right for you.
What Do the Results Mean?
The QuantiFERON-TB Gold blood test will come back with either a positive or a negative result. In some people, an inconclusive result may occasionally occur. A negative result means that there is not active or latent tuberculosis infection. A positive result is an indication that there is an infection that is present and that follow-up treatment may be necessary.
An inconclusive test is generally cause by a laboratory error or a blood sample that has sat for too long.
The one issue that may present itself for some people is that blood test results must be processed within 12 hours of collection in order for the test to be accurate. For medical providers that must ship out blood draws to a laboratory for this test, it may be impossible for the sample to reach the lab in time. In these instances, the TST is still the best choice.
The QuantiFERON-TB Gold blood test may be a more accurate diagnostic tool, but it is not considered a complete replacement for a medical provider’s personal judgment. For those who have had repetitive TSTs in the past and need a definitive result, then this blood test may be able to provide it.