science

Quantiferon

Quantiferon is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Quantiferon rather than just read about it. In short: An interferon-gamma release assay (IGRA) is a diagnostic tool for indicating a latent tuberculosis infection (LTBI). IGRAs are surrogate markers of Mycobacterium tuberculosis infection and indicate a cellular immune response to M. tuberculosis if the latter is present.

Key takeaways

Quantiferon belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Quantiferon to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Quantiferon from memory before moving on to harder problems.

Reference excerpt

An interferon-gamma release assay (IGRA) is a diagnostic tool for indicating a latent tuberculosis infection (LTBI). IGRAs are surrogate markers of Mycobacterium tuberculosis infection and indicate a cellular immune response to M. tuberculosis if the latter is present.

Active vs latent tuberculosis IGRAs cannot distinguish between latent infection and active tuberculosis (TB) disease, and should not be used as a sole method for diagnosis of active TB, which is a microbiological diagnosis. A positive IGRA result may not necessarily indicate TB infection, but can also be caused by infection with non-tuberculous mycobacteria. A negative IGRA does not rule out active TB disease; a number of studies have shown that up to a quarter of patients with active TB have negative IGRA results.

BCG status Because IGRAs are not affected by Bacille Calmette–Guérin (BCG) vaccination status, IGRAs are useful for evaluation of LTBI in BCG-vaccinated individuals, particularly in settings where BCG vaccination is administered after infancy or multiple (booster) BCG vaccinations are given. In contrast, the specificity of tuberculin skin test (TST) varies depending on timing of BCG and whether repeated (booster) vaccinations are given.

Commercial IGRA test Quantiferon, also known as QFT, is the registered trademark of an interferon gamma release assay (IGRA) for tuberculosis diagnosis manufactured by QIAGEN. The QFT-GIT assay is an ELISA-based, whole-blood test that uses peptides from three TB antigens (ESAT-6, CFP-10, and TB7.7) in an in-tube format. The result is reported as quantification of IFN-gamma in international units (IU) per mL. An individual is considered positive for M. tuberculosis infection if the IFN-gamma response to TB antigens is above the test cut-off (after subtracting the background IFN-gamma response in the negative control).

Mantoux vs IGRA test Since IGRAs are more costly and technically complex to do than the Mantoux test, in their 2011 policy statement, the WHO did not recommend replacing the Mantoux test by IGRAs as a public health intervention in low- and middle-income countries.

Quantiferon-TB (QFT) Quantiferon-TB Gold In-Tube (QFT-GIT), the third generation test, has replaced Quantiferon-TB (QFT) and Quantiferon-Gold, which are no longer marketed. According to the U.S. Centers for Disease Control, in 2001, the Quantiferon-TB test (QFT) was approved by the Food and Drug Administration (FDA) as an aid for detecting latent Mycobacterium tuberculosis infection. This test is an in vitro diagnostic aid that measures a component of cell-mediated immune reactivity to M. tuberculosis. The test is based on the quantification of interferon-gamma (IFN-γ) released from sensitized lymphocytes in whole blood incubated overnight with purified protein derivative (PPD) from M. tuberculosis and control antigens. Tuberculin skin testing (TST) has been used for years as an aid in diagnosing latent tuberculosis infection (LTBI) and includes measurement of the delayed type hypersensitivity response 48–72 hours after intradermal injection of PPD. TST and QFT do not measure the same components of the immunologic response and are not interchangeable. Assessment of the accuracy of these tests is limited by lack of a standard for confirming LTBI. As a diagnostic test, QFT:

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Quantiferon

Start with the simplest possible case. Write down what Quantiferon claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Quantiferon before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Quantiferon ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Quantiferon

In research: Quantiferon appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Quantiferon in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Quantiferon is common in secondary-school and first-year university syllabi. It links to neighbouring topics Immunologic tests, Tuberculosis, so understanding it makes those chapters shorter.
In everyday life: Look for Quantiferon outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Quantiferon in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Quantiferon means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Quantiferon out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Quantiferon in simple terms?

Why does Quantiferon matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Quantiferon?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Quantiferon.