Positive for antibodies to Mycobacterium tuberculosis 678 Concise Book of Medical Laboratory Technology: Methods and Interpretations In addition to the control band, a purple band appears

 

Summary

Lack of specificity of AFB smear, delayed reporting of

mycobacteria by culture and requisite of expertise and

expensive newer automated techniques, has led to the

Serology/Immunology 677

development of rapid and relatively simple serological

tests based on the detection of serum antibodies to

selected mycobacterial antigens, 38 kDa and LAM.

Principle

Serocheck-MTB utilizes the principle of immunochromatography. As the test sample flows through the

membrane assembly of the device, after addition of the

sample running buffer, the colored recombinant tuberculosis

antigens (38 kDa/ LAM) –colloidal gold conjugate complexes

with Mycobacterium tuberculosis specific antibodies in the

sample. This complex moves further on the membrane to

the test region where it is immobilized by the recombinant

tuberculosis antigens (38 kDa/LAM) coated on the

membrane leading to formation of a purple colored band

which confirms a positive test result for tuberculosis.

The unreacted conjugate and rabbit immunoglobulin

conjugated to colloidal gold move further on the membrane

and are subsequently immobilized by the antirabbit

antibodies coated on the membrane at the control region,

forming a purple colored band. This control band serves to

validate the test results.

Reagents and Materials Supplied

Each kit contains

A. Individual pouches, each containing:

1. Test device: Membrane assembly pre-dispensed with

recombinant tuberculosis antigens (38 kDa/LAM)

– colloidal gold conjugate, rabbit immunoglobulincolloidal gold conjugate, recombinant tuberculosis

antigens (38 kDa/LAM), and anti-rabbit antibody at

the respective regions.

2. Disposable plastic sample dropper

3. Desiccant pouch.

B. Sample running buffer in a dropper bottle

C. Package insert.

Storage and Stability

The test kit may be stored between 4–30°C till the duration

of the shelf-life as indicated on the pouch/corton. Do not

freeze.

Note

1. For in vitro diagnostic use only. Not for medicinal use.

2. Do not use beyond expiry date.

3. Do not intermix reagents from different lots.

4. Read the instructions carefully before performing the

test.

5. Handle all specimens as potentially infectious.

6. Follow standard biosafety guidelines for handling and

disposal of potentially infective material.

Specimen Collection and Preparation

No special preparation of the patient is necessary prior to

specimen collection by approved techniques. Though fresh

serum/plasma is preferable, specimens may be stored at

2–8°C for upto 24 hours, in case of delay in testing. Blood

samples collected with a suitable anticoagulant such as

EDTA or Herparin or Oxalate can also be used. Do not

freeze whole blood samples. Do not use turbid, lipamic

and hemolyzed serum/plasma specimens. Do not use

hemolyzed, clotted or contaminated whole blood samples.

Testing Procedure and Interpretation of Results

1. Bring the Serocheck-MTB kit components to room

temperature before testing.

2. Open the pouch and remove the device, sample

dropper and desiccant. Check the color of the

desiccant. It should be blue. If it is turned colorless or

pink, discard and use another device. Once opened,

the device must be used immediately.

3. Label the test device with patients identity.

4. Tighten the vial cap of the sample running buffer

provided with the kit in the clockwise direction to

pierce the dropper bottle nozzle.

5. Add one drop of serum/plasma or whole blood with

the sample dropper provided in the sample port ‘A’.

6. Dispense 5 drops of sample running buffer into

port ‘B’, by holding the plastic dropper bottle vertically.

7. At the end of 15 minutes read the results as follows.

Negative for antibodies to Mycobacterium

tuberculosis

Only one purple band appears in the control window ‘C’.

Positive for antibodies to Mycobacterium tuberculosis

678 Concise Book of Medical Laboratory Technology: Methods and Interpretations  In addition to the control band, a purple band appears

in the test window ‘T’.

8. The test should be considered invalid if no bands

appear on the device. Repeat the test with a new device

ensuring that the test procedure has been followed

accurately.

Limitations of the Test

1. As with all diagnostic tests, the test results must always

be correlated with clinical findings.