JV Gopinath, National Sales Manager-Critical Diagnostics Division, Meril Diagnostics

The current trend in assays for certain infectious parameters in clinical pathology laboratories, nursing homes, physician clinics/offices demands highly sensitive assays
that are quick, simple, and easy to perform
and those which require minimal or no instrumentation.

Prior to the development of viral antigen and NAA tests, serological-based tests were used for diagnosis and still remain the commonly used tests for many viruses.

Currently, immunochromatography tests are available in different formats, one of which is immunoconcentration or flow through the devices based on immunoconcentration (Dotblot) assays that uses membranes or glass fiber filters as solid phase with large surface that allows the flow of the sample. The sample passing through the membrane gets concentrated and accelerates the binding of antigens and antibodies. This technology has provided an answer to the need for simple, highly sensitive assays that can be easily interpreted within a few minutes.

These assays produce a well-circumscribed colored dot on the solid phase surface if the test turns to be positive. These tests also allow the differentiation of the species like in case of HIV antibody tests. The protocol of these tests includes multiple steps that include drop-wise addition of buffer, samples, and conjugates. The assay also includes a built-in control to verify the correct protocol. The control mainly uses antihuman immunoglobulin that binds any immunoglobulin in the sample and produces a separate indicator when all reagents are added appropriately.

Early antibody tests used viral lysate as the source of HIV antigenic material, which proved to have significant batch-to-batch variations leading to false positivity. Later, recombinant and synthetic antigens were used to help in providing better, stable, and sensitive test systems. The introduction of antigen sandwich principle improved the detection of IgM antibodies, thus considerably improving sensitivity for early seroconversion.

Synthetic peptides representing relevant B-cell epitopes are, potentially, perfect antigens to be used in diagnostic assays because of their much higher specificity as compared to those of biologically derived molecules. It is thus not a surprise that an increasing number of synthetic peptide-based diagnostic assays are being developed or are already commercially available.

Quadro – 4 dot rapid test kits based on the principle of immunoconcentration for detection of antibodies against HIV I and II manufactured by Meril will help the laboratories to generate reports more accurately and precisely. The kit utilizes synthetic antigens as well as recombinant antigens, which are uniquely formulated. The synthetic antigens detect antibodies against the serotype-specific linear epitopes and the recombinant antigens detect the antibodies against the conformational epitopes. The use of both types of antigens collectively increases the specificity and the sensitivity of the kit. The kit is capable of detecting antibodies against all groups of HIV including subtype 'C'.

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