pathology and diagnostics
Point of care testing in virology
The increasing range and scope of point of care tests in virology means that these assays have the potential to make a valuable contribution to diagnostic virology services
Sarah Pitt PhD CSci FIBMS School of Pharmacy and Biomolecular Sciences , University of Brighton , Brighton , UK
The role of the diagnostic virology laboratory in patient care has changed markedly in recent years . Twenty years ago , the work involved growing viruses from patient specimens or detecting evidence of a change in concentration in serum antibodies in response to a viral infection . In most cases , it would take several weeks to achieve a final result . However , in the 21st century , virologists have the technology and scientific expertise to be much more responsive both in terms of diagnosing commonly encountered viral infections and in dealing with new and emerging viruses . 1 Culture of viruses from respiratory and faecal samples in cell lines has largely been replaced by detection of the viral genome by molecular methods , particularly polymerase chain reaction ( PCR ). Instead of collecting a blood sample during the acute phase of the infection and another sample two weeks later , in order to compare antibody titres , enzyme immunoassay ( EIA ) is now used to identify specific antibodies when the patient presents with the symptoms . Both of these approaches allow the laboratory to provide a result in days ; where it is clinically relevant , it can be possible for the sample to be processed , tested and the results interpreted in less than 24 hours .
However there is an increasing repertoire of point of care tests ( POCTs ) for viral diagnosis on the market . These offer the prospect of an answer in a matter of hours without the need to transport the sample from the hospital ward or primary care centre to the virology department and wait for the laboratory to communicate their findings . These POCTs – also known as near patient tests ( NPTs ) or rapid diagnostic tests ( RDTs ) – can be useful in patient care and management because they are easy to use and can often give a result in a relatively fast time . However , it should be borne in mind that they are not always as accurate as the equivalent test performed by scientists in the main laboratory and they are usually more expensive . Therefore the decision to introduce a POCT into a particular situation needs careful consideration . 2 There are some interesting examples of their implementation into diagnostic virology . The types of POCT formats currently available to detect evidence of viral infection fall into two broad formats – lateral flow assays ( LFAs ) and desk top molecular analysers .
LFAs LFAs comprise test strips made of a material such
152 HHE 2018 | hospitalhealthcare . com as cellulose and embedded with biological markers ( specific antibodies or antigens ). The strip is held in a plastic case to keep it dry and clean and there is an opening for the patient ’ s sample to be added . The most familiar example is home pregnancy testing kits . In virology , formats are available to detect either the presence of the virus itself , in specimens such as faeces or throat swabs , or specific serum antibodies against particular pathogens . The principle is similar to the EIA . The sample flows across the test strip and activates the reagents . If a reaction between occurs between the virus ( or antibody ) from the patient and a marker in the test strip , a visible colour change will occur . 3 The devices require small volumes of a type of sample , which can be collected relatively easily from a patient . The sample is treated with a reagent to release the virus particles or antibodies from cellular material and enhance their binding reaction to the relevant marker ( s ) in the test . Figure 1 shows an LFA for detection of norovirus in faecal samples . In this case , no virus was detected , but note the activation of the control line in the strip , which indicates that the test was carried out correctly . All the necessary reagents and equipment are included in the kits so that anyone who has been trained properly can perform and interpret an LFA . The time it takes to get a result varies slightly depending on the particular assay , but including the specimen preparation step and the time taken to read the results , it usually takes less than 30 minutes .
Desk top molecular analysers A large proportion of the work in a modern diagnostic virology laboratory involves detection and sequencing of viral genomes . The assays use the principle of nucleic acid amplification ( for example , PCR ), which in theory can recognise a single molecule of viral RNA or DNA and copy it multiple times to increase its concentration to a level that is possible to measure . The technique involves a number of steps , including extraction of the nucleic acid from the cellular material in the patient ’ s sample , running the amplification steps and then detecting the resulting RNA or DNA copies . It requires scientific understanding , technical expertise and dedicated laboratory space . This is needed not only to accommodate the various analysers , but also to maintain an environment free of stray pieces of nucleic acid ( for example , from the scientists ’ skin or hair ).