¾ In patients affected by extrapulmonary tuberculosis, the test will be effective according to the organ infected. ¾ In 10 to 20% of the patients, the humoral immunologic

 

2. The results of the test are to be interpreted within the

epidemiological, clinical and therapeutic context.

3. Any modifications to the above procedure and/or use

of other reagents will invalidate the test procedure.

4. Do not compare the intensity of the test line and

control line to determine the concentration of the

antibodies in the test specimen.

5. Testing of pooled samples is not recommended.

6. In immunocompromised TB patients, such as in

patients with HIV, since antibodies to Mycobacterium

tuberculosis may not be present at levels indicative of

active disease, and the test may give a negative results.

7. Patients with recent case of active tuberculosis

infection may continue to have antibody titer within

the detectable limits of the test and such samples may

give a positive test results, after such patients have

been cured.

8. Positive test results may be obtained in Leprosy

patients. However, the clinical presentation of leprosy

cannot be confused with that of tuberculosis.

TB IgG, IgA, IgM AB, MFD. ANDA

(Courtesy: Lilac Medicare)

In vitro diagnostic test: Enzyme immunoassay for the

Determination of IgA, IgG or IgM antibodies against

mycobacteria in human serum.

Serodiagnosis of Mycobacterial Infections

The A60 antigen complex is an inter-specific antigen

found in the cytosol of typical and atypical mycobacteria.

It reacts with antibodies created during mycobacterial

infections (tuberculosis, leprae, etc.), and also reacts with

the antibodies produced during Nocardia infections.

Antimycobacterial antibodies are absent in healthy

individuals. However, inapparent or abortive infections

due to mycobacteria are much more frequent than usually

suspected. In particular, IgM antibodies are frequently

observed after a contact inherent to professional

occupations (e.g. hospital personnel and social workers)

or to adverse social conditions.

In the latter case, the positive IgM reaction is observed

most readily among babies and infants growing in

unhealthy conditions. A positive IgM test observed in the

serum and CSF is most useful in establishing the diagnosis

of tuberculous meningitis for the serodiagnosis of latent

pulmonary or extrapulmonary tuberculous primary

infection and for the prognosis of relapses.

The large amount of work that has been carried out

to establish the clinical validity of the Anda-Tb IgG test

allowed the following conclusions to be drawn:

¾ Healthy people are negative, even if they have a positive

intradermal reaction and even if they live in a country

with severe endemy.

¾ The prevalence of inapparent subclinical infections is

largely under-evaluated in the third-world, but also

in developed countries among certain social and

professional groups: people in regular contact with

individuals belonging to the third or fourth-world (e.g.

food store employees, hospital personnel and jailed

people), non-tuberculous diseased people, positive HIV

patients in hospitals and others. All show a percentage of

A60 seropositives, sometimes well superior to that seen

in the population at large which presents a frequency of

positives fluctuating between 1.5 and 3%.

¾ In patients suffering from a tuberculous infection, the

test shows the presence of IgG antibodies if the patient

has undergone an antigenic booster stimulus. The

test will be positive mostly in cases of patent active

infection. It will also be positive in case of a booster

vaccination in healthy people.

¾ In patients affected by extrapulmonary tuberculosis,

the test will be effective according to the organ infected.

¾ In 10 to 20% of the patients, the humoral immunologic

activity is weak. Patients showing such an anergy may

appear negative.

¾ Tuberculous meningitis provokes the formation of

antibodies in the cerebrospinal fluid (CSF), detectable

at a 1:10 dilution.

The presence of IgG antibodies indicates a good

immunological response of the patient to the infection. An

anergy affecting some patients before or at the beginning of

the treatment concerns as well the cellular immunity (PPD)

as the IgG output. The production of IgA antibodies is

largely independent from the production of IgG antibodies

and may occur while the patient is in an IgG anergic state.