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Complex RNA Probe-Based Test for Mycobacterium tuberculosis Detection (Serum/Plasma)

Published: August 9, 2026Updated: August 16, 2026

This test measures genetic material from *Mycobacterium tuberculosis* (TB bacteria) in your blood or plasma using a specialized probe. It helps detect active TB infection when traditional tests may not be conclusive.

Quick summary

["Assists in diagnosing TB when other tests are inconclusive or early-stage infection is suspected."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
38378-6
Short code
Deprecated M TB Cmplx rRNA XXX Ql Prb
Synonyms
Deprecated M TB Cmplx rRNA XXX Ql Prb
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
probe
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

How the Test Works

The test uses a highly sensitive probe to detect RNA fragments from *M. tuberculosis*. These fragments are released when the bacteria are active. The probe binds to these RNA sequences, allowing for detection even in low concentrations of the bacteria.

When You Might Need This Test

Your healthcare provider may recommend this test if you have symptoms of TB (such as persistent cough, fever, or weight loss), if traditional tests (like sputum culture) are negative but TB is suspected, or if you’re at higher risk for TB (e.g., recent travel to high-risk areas, weakened immune system).

Sample Collection and Preparation

A blood sample is drawn from a vein, usually in your arm. The blood is then processed to separate plasma (the liquid part containing the TB RNA probe). This sample is sent to a lab for analysis.

What to Expect Before the Test

No special preparation is typically needed. However, if you’re on certain medications (like some antibiotics or immunosuppressants), let your provider know—this may affect results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

This test is particularly useful for diagnosing active TB in people with negative or slow-growing traditional tests. It can also help monitor treatment response by detecting RNA before bacterial cultures become positive. However, false negatives can occur if the bacteria are not actively replicating, so results should always be interpreted by a healthcare provider.

Short name

TB RNA Probe Test (Serum/Plasma)

Frequently asked questions

Why might my test results be positive?
A positive result strongly suggests active *M. tuberculosis* infection. This could mean you have TB, especially if you have symptoms like coughing, fever, or weight loss. Your doctor will work with you to determine the next steps, which may include further testing or starting treatment.
Could this test give a false positive?
While rare, false positives can happen if you’ve recently been exposed to TB bacteria or if you have other infections that trigger similar immune responses. Your healthcare provider will review your medical history and other test results to confirm the diagnosis.
What if my test is negative but I still have TB symptoms?
A negative result means the test did not detect TB RNA in your sample. However, TB can sometimes be difficult to diagnose, especially in early stages. If you continue to have symptoms, your doctor may order additional tests (like a sputum culture or chest X-ray) or repeat this test. Never stop taking prescribed medications without consulting your provider.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy