The Quantiferon-TB Gold Plus test, also known as an Interferon-Gamma Release Assay (IGRA), is a blood test designed to detect infection with Mycobacterium tuberculosis (TB bacteria). It identifies whether an individual’s immune system has been exposed to TB by measuring the cell-mediated immune response, specifically the reaction of T cells to specific TB proteins. This test serves as a modern alternative to the traditional tuberculin skin test, particularly beneficial for individuals who have received the BCG vaccine.
Standard Turnaround Time
Results for the Quantiferon-TB Gold Plus test typically become available within two to five business days. Some laboratories may report results faster, within 24 to 48 hours, while others might take up to five to seven days. This timeframe includes sample transportation and laboratory processing.
Once blood is drawn, it is incubated for 16 to 24 hours to allow for this immune response to occur. Following incubation, the blood plasma is analyzed using an enzyme-linked immunosorbent assay (ELISA) to quantify the IFN-γ produced. This process contributes to the standard turnaround time.
Influences on Result Delivery
Several factors can influence how long it takes for Quantiferon test results to be delivered, potentially extending the typical waiting period. One significant factor is the volume of tests being processed by the laboratory; a high influx of samples can lead to delays. The transportation of the blood sample from the collection site to the testing laboratory also plays a role, as specimens are time-sensitive and must reach the lab within 14 to 16 hours of collection, maintained at room temperature. Any logistical challenges in shipping can add to the overall wait time.
Weekend and holiday closures at testing laboratories can further extend the delivery of results, as processing may not occur on non-business days. Another potential cause for delay is the need for retesting. If the initial blood sample is compromised during collection or transport, or if the test yields an indeterminate result, a new sample may be required. Indeterminate results, which mean the test was unclear, can occur due to factors like a compromised immune system or improper handling of the blood specimen.
Finally, once the laboratory completes the analysis, results are typically sent to the ordering healthcare provider. There might be an additional period for the provider’s office to review these results and then communicate them to the patient. This final step in the communication chain can add variability to the total time a patient waits to receive their information.
Understanding What Your Results Mean
Upon completion of the Quantiferon-TB Gold Plus test, the results will generally fall into one of three categories: positive, negative, or indeterminate. A positive result indicates that it is likely an individual has been infected with Mycobacterium tuberculosis bacteria. It is important to understand that a positive result does not differentiate between a latent TB infection, where the bacteria are present but inactive, and active TB disease. Further medical evaluations, such as a chest X-ray or sputum tests, are typically necessary to determine if active disease is present.
Conversely, a negative result suggests that infection with Mycobacterium tuberculosis is unlikely. However, in cases where there is a strong suspicion of exposure to TB, a healthcare provider might recommend retesting to confirm the negative finding. This ensures accuracy, especially when clinical factors suggest a potential for infection.
An indeterminate result means the test could not provide a clear positive or negative outcome. This can happen if the immune response in the sample was too low or too high, or if there were issues with the sample itself, such as incorrect handling or insufficient lymphocytes. In such instances, retesting is often recommended, or the healthcare provider may pursue alternative diagnostic approaches. Regardless of the outcome, discussing the results with a healthcare provider is essential for accurate interpretation and to determine any necessary next steps, including further testing or treatment.