In the world of laboratory diagnostics, QuantiFERON (for tuberculosis) and blood titer (antibody) tests are two important tools that provide insights into exposure to infectious agents, immune status. In this blog, we’ll explain what each test measures, when and why you might use them, how to interpret results, limitations and pitfalls, and how you can order them via eNational Testing.

What Is QuantiFERON (TB Blood Test)?

QuantiFERON (often “QuantiFERON-TB Gold” or “QFT-Plus”) is a blood-based interferon-gamma release assay (IGRA) used to detect tuberculosis (TB) infection — either latent (inactive) or in some cases active exposure.

How QuantiFERON Works

1. A blood sample is drawn into special tubes containing TB-specific antigens (e.g. ESAT-6, CFP-10).
2. White blood cells in the sample (if sensitized by past TB exposure) will release interferon-gamma when exposed to these antigens.
3. The test measures how much interferon-gamma is released, subtracting background (nil control) — and compares it to a positive control (mitogen) to validate that the immune system responded properly.

1. Based on thresholds, the result is interpreted as negative, positive, or indeterminate (if the controls fail).

Compared with the traditional TB skin test (Mantoux / PPD), QuantiFERON offers advantages such as:

• Only one visit required (blood draw in a single appointment) rather than returning in 48–72 hours.
• Less interference from prior BCG vaccination (since the antigens used are not present in the BCG vaccine).
• Objective, laboratory-based readout rather than subjective reading of skin induration.

However, QuantiFERON cannot distinguish active TB disease from latent TB infection, and a positive result should always be followed by further clinical evaluation (e.g. chest imaging, symptom assessment).

When and Why Use QuantiFERON

You might order a QuantiFERON test in these contexts:

• Screening individuals who have had exposure to TB (contacts, immigrant health screening, occupational health)
  
  
• Before initiating immunosuppressive therapy (biologics, steroids) to screen for latent TB reactivation risk
• In persons with BCG vaccination history, where PPD may be unreliable
  
  
• In cases where return for PPD reading may not be feasible
  
  

If you'd like to offer QuantiFERON testing to your clients, you can direct them to: QuantiFERON-TB Gold – eNational Testing

Understanding Blood Titers (Antibody Titers)

While QuantiFERON provides evidence of TB immune response, blood titer (antibody titer) tests assess the presence and concentration of specific antibodies in the blood. They are frequently used to gauge immunity, past exposure, or determine need for booster vaccines.

What Is a Titer Test?

• A titer is a measurement of how much an antibody is present in a sample — expressed as a ratio (e.g. 1:40, 1:160).
• It typically involves serial dilutions: the highest dilution at which antibody is still detectable yields the titer.
• Depending on the antigen/virus being tested, the titer will be compared with reference thresholds to determine if immunity is “protective.”

Common titers include measles, mumps, rubella (MMR), varicella (chickenpox), hepatitis A/B, rubella (IgG), etc.

Why Are Titer Tests Useful?

• Confirming immune status: especially when vaccination records are incomplete or outdated.
• Determining whether boosters are needed (if protection has waned from prior vaccination)
• Meeting requirements for healthcare employment, school, travel
  
  
• Checking vaccine response in special populations (e.g. post-transplant, immunosuppressed)
  
  

Interpreting Titer Results

• A positive / above-threshold titer suggests likely immunity (or prior exposure)
  
  
• A negative / below-threshold titer suggests susceptibility and possibly need for vaccination
  
  
• Titers are antigen-specific: a “protective” titer for measles won’t tell you anything about varicella
  
  
• Over time, titers may decline; a person with a historically protective titer may drop below threshold and require a booster
  
  
• In some cases, “borderline” or equivocal titers require repeat testing or clinical judgment
  
  

Note that the clinical significance of titers can vary depending on assay, lab reference ranges, and patient population.

QuantiFERON / Blood Titers – eNational Testing
eNational Testing

How QuantiFERON and Titer Tests Fit in Clinical Workflow

Advantages, Limitations & Pitfalls

QuantiFERON: Strengths & Caveats

Strengths:

• One-visit test; objective readout
  
  
• More specific than PPD in BCG-vaccinated individuals
  
  
• Rapid turnaround (typically 3–5 days)

Limitations / potential pitfalls:

• Indeterminate results: may occur if the positive control (mitogen) fails to stimulate, especially in immunosuppressed individuals
  
  
• False negatives: early infection, immunocompromise, or improper specimen handling can lead to falsely negative results
• It cannot distinguish latent vs active disease — further clinical workup is required
  
  
• Sometimes cross-reactivity with non-tuberculous mycobacteria (though limited)

Titer Tests: Strengths & Caveats

Strengths:

• Offers direct evidence of immune status (antibody presence)
  
  
• Helps avoid unnecessary revaccination; you only vaccinate if titer is low or absent
  
  

Limitations / pitfalls:

• Because labs, pathogens, and assays differ, protective titer thresholds vary
  
  
• A “positive” titer doesn’t guarantee 100% protection, especially in immunocompromised states
  
  
• Titers can wane over time; someone immune in the past may lose adequate protection
  
  
• Some antigens don’t have well-defined protective cutoffs
  
  

How to Order These Tests via eNational Testing

Here are direct links to the relevant test offerings on eNational:

• QuantiFERON-TB Gold – order the TB-exposure blood test here:
  https://www.enationaltesting.com/tests/23-blood-titers/quantiferon-tb-gold
  
  
• QuantiFERON / Blood Titers (Antibody Titer tests) – this category page lists QuantiFERON plus a selection of antibody titer tests (e.g. for measles, hepatitis, etc.)

Practical Tips & Best Practices

1. Pair tests appropriately
   
   

• In occupational settings (e.g. healthcare, clinics), it is common to pair TB screening (QuantiFERON) and immunity titers (MMR, varicella, hepatitis) so that all necessary compliance requirements are met in a single visit.
  
  
• Ordering both upfront can save multiple clinic visits or specimen draws
  
  

• Encourage users to review results with a qualified clinician (especially for positive or indeterminate QuantiFERON results, or low antibody titers in vulnerable populations)
  
  
• Remind them that a negative QuantiFERON does not rule out TB in all cases (especially with symptoms or immunodeficiency)
• In the case of antibody titers, sometimes a borderline result may warrant recheck or clinical correlation
  
  

• Users should keep a copy of their positive QuantiFERON or positive titer results for future need (occupational, travel, healthcare)
  
  
• Some individuals will test positive on QuantiFERON for life (i.e. prior latent TB) — it's helpful to know baseline results
  
  

• Since titers can wane, users may want to repeat titers periodically, especially if at increased risk or in settings with vaccine mandates