distinguished from other disorders. Recently developed, IgM capture assays provide the clinician with a helpful and reliable test, not affected by rheumatoid factor.

 

The unreacted conjugate and unbound complex, if any,

move further on the membrane and are subsequently

immobilized by the antirabbit antibodies coated on the

membrane at the control region ‘C’, forming a colored

band. This control band serves to validate the reagent and

assay performance.

FIG. 22.27: Virucheck result reading

666 Concise Book of Medical Laboratory Technology: Methods and Interpretations Reagents and Materials Supplied

Kit Components

1. Flavicheck-HCV membrane test assembly (device)

comprises of HCV specific recombinant antigencolloidal gold conjugate co-dispensed with rabbit

IgG colloidal gold conjugate; predispensed with HCV

specific recombinant antigen at region T’, and antirabbit antiserum predispensed at the region ‘C’, along

with a plastic sample dropper and desiccant.

2. Package insert.

Storage and Stability

The test kit should be stored between 4–30°C for the

duration of the shelf-life of the kit as indicated on the

pouch/kit label.

Note

1. In vitro diagnostic test. Not for medicinal use.

2. Do not use beyond expiry date.

3. Read the package insert carefully before performing

the test.

4. Handle all specimen as potentially infectious.

5. Follow standard biosafety guidelines for personal

protection, handling and disposal of potentially

infectious material.

Specimen Collection and Preparation

1. No prior preparation of the patient is required before

sample collection by approved techniques.

2. Fresh serum/plasma is preferable. Serum/plasma may

be stored at 2 to 8°C up to 24 hours in case of delay in

testing. For long-term storage, freeze the specimen at

–20°C for 3 months or –70°C for longer periods.

3. Repeated freezing and thawing of the specimen should

be avoided.

4. Do not use hemolyzed, clotted, contaminated,

viscous/turbid specimen.

5. Specimen containing precipitates or particulate matter

must be centrifuged and the clear supernatant only

used foresting.

6. Do not heat inactivate the sample.

Test Procedure and Interpretation of Results

1. Let the sealed pouches attain room temperature

(25–30oC).

2. Tear open the sealed pouches and retrieve the

appropriate number of test devices as required.

Label the test devices appropriately. Once opened,

the devices must be used immediately. The addition

of sample must be done at the center of the sample

port holding the sample dropper in a vertical

position. Ensure the drops are free falling. Use a new

sample dropper for each specimen to avoid cross

contamination.

3. Dispense two drops of specimen in to the sample port

(S) using the dropper provided.

4. At the end of 15 minutes, read the results as follows:

Negative Test Result

Appearance of only one colored band at the control

region’C’.

Positive Test Result

Appearance of a colored band at the test region ‘T’in

addition to the band at control region ‘C’.

5. The test should be considered invalid if neither the test

nor the control bands appear. Repeat the test with a

new device.

6. Based on the concentration of antibodies to HCV in

the specimen a positive result may start appearing as

early as 2 minutes, however, negative results must be

confirmed only at the end of 15 minutes.

7. In case of doubtful results at 15 minutes, the test

may be extended up to a maximum of 30 minutes if

required.

Remarks

1. Though Flavicheck-HCV is a sensitive and reliable

screening test, it should not be used as a sole criterion

for diagnosis of HCV infection.

2. All positive specimen should be further tested using

appropriate supplemental confirmatory tests. Test

samples that are positive by a third generation

double antigen sandwich-based assays may be

reactive with very early seroconversion samples,

which are negative/intermediate with blot-based

assays. Such samples should be reconfirmed with the

RNA-PCR-based method or must be followed up for

seroconversion at a later date.

3. As with all diagnostic tests, results must be correlated

with clinical findings to arrive at the final diagnosis.

Serology/Immunology 667

4. Absence of antibodies to HCV does not indicate that

an individual is absolutely free of HCV infection

as the collection of sample and its timing vis-a-vis

seroconversion will influence the test outcome.

5. Do not compare the intensity of test lines and the

control lines to judge the concentration of antibodies

in the test specimen.

6. Since various tests for HCV differ in their performance

characteristics and antigenic composition, their

reactivity patterns may differ.

7. Testing of pooled samples is not recommended.

TORCH Infections: Introduction

Toxoplasma Infection

Toxoplasma gondii is an obligate intracellular protozoan

parasite that is probably capable of infecting all species of

mammals, including man. The detection of IgM antibodies

to T. gondii is particularly helpful for the diagnosis of acute/

primary infections in “risk” individuals in association with

AIDS, organ transplantation and pregnancy. As most

of Toxoplasma infections are mild or asymptomatic in

otherwise healthy individuals, the detection of T. gondiispecific IgM, in absence of detectable specific IgG, has

become important for the monitoring of primary infections

in pregnant women, as the parasite can lead to birth

defects. Moreover, as T. gondii infections are most severe

in immunocompromised patients, where the disease can

be fatal, acute infections due to this parasite have to be

distinguished from other disorders. Recently developed,

IgM capture assays provide the clinician with a helpful and

reliable test, not affected by rheumatoid factor.

Rubella Infection

Infection with Rubella virus in children and adults

is a self-limited, mild disease characterized by an

erythematous rash, mild upper respiratory symptoms

and suboccipital lymphadenopathy. After recovery, the

individual is immune to subsequent infection with rubella

virus. Primary infection of a pregnant woman, however,

particularly in the first trimester of pregnancy, may result

in a high risk of fetal infection with severe complications.

Congenital Rubella is characterized by cataracts, deafness,