Why false positive HIV test can mislead clinicians

Many people working in the health sector are always scared of possible viral infection due to constant contact with patients’ blood and body fluids. This scares some people from joining the health profession as the lives saved could cost their lives.
 Dr. Joseph Kamugisha
Dr. Joseph Kamugisha

Many people working in the health sector are always scared of possible viral infection due to constant contact with patients’ blood and body fluids. This scares some people from joining the
health profession as the lives saved could cost their lives.

However the rise of vaccine to hepatitis B that is highly contagious has lessened the burden of hepatitis B infection amongst health workers.  But there is still no vaccine for hepatitis C and HIV viruses that are potentially more dangerous and aggressive but with less contagiousity.

Hepatitis C and HIV main channel of transmission is through blood or human body fluids.

For these viruses, diagnostic tests can be done by rapid tests, Elisa, western blot and DNA polymerase chain reaction (PCR).

In order to confirm that an individual is infected with either of the viruses, all the four tests have to be performed in different phases.

For example the HIV antibody tests seen in ELISA tests commonly and found in the hospital centers do not only detect viruses’ specific to HIV infection simply because they can react with an assortment of other proteins found in blood.

Here what happens actually is that a sample of blood serum is incubated with a mixture of these proteins in a test known as ELISA. The ELISA becomes positive when the solution changes colour thereby indicating a reaction between the proteins in the ELISA test with the patient’s antibodies.

However based on a number of cases seen in the hospital setups, the ELISA is not specific meaning that it can react in absence of HIV infection.

This is why it is very wrong to consider a person infected with HIV basing on results from ELISA alone. It is important to repeat serum tests with Western Blot that will be able to test many
viral proteins.

Here the positive tests are read by bands that show up in order to confirm a positive reaction. However certain combination of bands can be defined as positive test. The accuracy of these
tests also depends on the environment and location of the patient testing’s. This means its accuracy will also depend on a number of considerations.

The western blot is considered more specific at 99.9% and in most cases if positive the patient is infected. The doubt over antibody dependent ELISA kit test is on the basis that the immune system has the ability to detect foreign agents and to respond by producing antibodies which react with those foreign agents or infections to the body.

This also means that observation of an antibody reaction with a particular agent is not an automatic proof that the anti-body is produced in response to that agent. 

Antibodies that react with some viral proteins might react with other proteins as well and this means that false results can be shown up for a particular purpose.

For example some HIV patients might have antibody that reacts with various laboratory chemicals but no person has ever claimed to be infected with HIV through laboratory chemicals.

If you bring all these evidences for analysis, then you conclude that it is very wrong to pronounce HIV infection to a patient depending on only antibody reaction.

Another most accurate diagnostic test today for viral infection is the polymerase chain

reaction. It is a very sensitive technique that finds specific blueprints of viral genes. Genes do not react like chemicals neither they do form a mixture with other substances. This is why

PCR gives more precise diagnostic findings.In a confusing situation, viral load for HIV is performed to trace the possibility of a single or more viral presence in blood. If the viral load is found to be 0, then the patient is not infected with the virus and this is very conclusive.

Health experts should always be very careful before they start treatment regimens for their patients. Health workers should not subject potentially toxic HIV medications to non-infected

patients merely on the basis of poor perception of viral activity in the blood.

The writer is a resident oncologist in Jerusalem, Israel

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