As India opens up to new testing methods for Covid-19, approvals for importing kits, which use technology other than rapid antibody tests that rely on immunoglobulins, have received the drug regulator’s nod. Some of these kits would use chemiluminescent platforms, while others would use ELISA (enzyme-linked immunosorbent assay) platforms.
Multinationals, such as Abbott Healthcare and Roche Diagnostics, have received approval to import such kits. The controversy around the efficacy and the pricing of rapid tests has encouraged government agencies to look for other testing methods that would be relatively accurate as the country heads towards a graded exit plan from the nationwide lockdown.
An Abbott spokesperson said the firm was working with regulatory authorities to address the need for accurate testing. “We are working on several testing solutions for Covid-19 — from the core lab to point of care. This includes rapid tests that can detect antibodies on a finger prick, as well as core laboratory molecular tests (SARS-Cov-2 assay on m2000) that can be useful for screening larger populations”.
Abbott has approval for chemiluminescent microparticle immunoassay with Architect System that would be imported from Abbott Ireland. Roche has approval for a chemiluminescent technology called ECLIA (Elecsys Anti-SARS-Cov-2) that would be imported from Roche Germany.
Indian pharma firm Eris Lifesciences has approval to import fluorescent test kits from China’s Maccure Biotechnology and diagnostic lab Trivitron Healthcare has permission to import chemiluminescent kits from another Chinese firm, Shenzhen New Industries Biomedical Engineering.
There are two types of Covid-19 tests — antigen and antibody tests, and molecular tests. Molecular tests refer to reverse transcription polymerase chain reaction (RT-PCR), where a throat or nasal swab from the patient is used to detect presence of the virus RNA. For antigen-antibody tests, there are primarily three types — one is the rapid antibody test, another is ELISA and the third is chemiluminescent technology.
The antigen or antibody tests detect the presence of immunoglobulin M (IgM) or immunoglobulin G (IgG) antibodies in the blood sample. The immune system produces these antibodies in reaction to the viral infection — IgM in the initial stages and IgG in the later stages. These are mainly visual tests, that is, the detection is through colour change.
In the rapid antibody tests, the naked eye catches this colour change, and in case of a minor change, that may be missed. “But, in ELISA, the machine reads the colour, and the accuracy increases. While in chemiluminescent technique, the colour change is modified into light signals. That is more accurate,” explained a diagnostic firm owner. Rapid antibody test kits work like home pregnancy kits, which come with a test strip and a few drops of blood on the strip show results in 15 minutes or so.
The World Health Organization prefers ELISA over the rapid antibody tests. “ELISA is highly sensitive and specific and is able to detect HIV-1/ HIV-2 and variants. It requires sophisticated equipment, a constant supply of electricity, and skilled technicians. It is not suitable for small laboratories, but for testing large numbers of samples per day, as well as in blood banks or for surveillance studies. The rapid tests are better for emergency testing, and in smaller laboratories with low numbers of tests per day,” it said.