IMM 16: Introduction to Point of Care Testing Flashcards
What is point-of-care testing (POCT)?
form of testing in which the analysis is performed where the healthcare is provided close to or near the patient
What are the characteristics of POCT? (4)
- easy to use – no formal laboratory training required
- limited risk to the patient (even if performed incorrectly)
- easy to store – analyzer and test kit should have durable resistance during storage and use
- easy to access – readily available or accessible at pharmacies or primary care clinic
What are the benefits of POCT? (4)
- accessibility and convenience – can be performed and analyzed in close proximity to patient care sites, such as at a patient’s home or a pharmacy, and even in rural location
- smaller sample size – tests are often less invasive or require less patient sample compared to traditional laboratory tests
- faster results – often provide results within minutes, which may result in faster decision-making and treatment implementation
- streamlined workflow – do not require laboratory training, which allows for integration into various healthcare settings which can improve efficiency and reduce healthcare costs
What are the drawbacks of POCT? (2)
higher risk of external interference to standard laboratories due to:
- incorrect handling or sample collection by - inadequately trained staff
- inadequate or incorrect maintenance of POCT device
- inadequate or insufficient quality control checks and calibration of POCT device
reagents and test supplies can be costly for pharmacies
- not covered by Pharmacare
- some private insurance plans may cover the cost
What are the 2 types of point-of-care devices?
- lateral flow immunoassay
- molecular assay
What are immunoassays?
detect the specific interaction between antibodies and antigens
- antibodies (Y-shaped proteins) are secreted by the immune system B cells – these proteins bind to specific proteins or molecules, and this precision makes them a valuable tool in detecting targets of interest (ie. proteins, drugs, other antibodies, antigens)
- in direct assays, binding of antibody-analyte is detected (usually via fluorescence)
What are lateral flow immunoassays?
test strip contains specific antibodies or antigens that can bind to analytes including antigens, antibodies, and chemicals in patient sample
- sample migrates along the test strip through capillary action, and if the target substance is present, it will bind to coloured particles on the strip
- this binding generates a visible coloured line at the test line region, indicating a positive result for the target substance
What are molecular assays?
amplification of DNA/RNA fragments through polymerase chain reaction (PCR)
- presence of these fragments would indicate presence of disease
- often have higher sensitivity/specificity compared to antigen-based POCTs
Lateral Flow Assay vs. Molecular Assay
Principle
- lateral: capillary action
- molecular: nucleic acid amplification
Lateral Flow Assay vs. Molecular Assay
Equipment
- lateral: no external equipment
- molecular: required specialized equipment (PCR machine)
Lateral Flow Assay vs. Molecular Assay
Sensitivity and Specificity
- lateral: moderate (usually)
- molecular: relatively high (usually)
Lateral Flow Assay vs. Molecular Assay
Multiplexing
- lateral: limited – usually detects a single analyte
- molecular: can detect multiple analytes simultaneously
Lateral Flow Assay vs. Molecular Assay
Complexity of Use
- lateral: simple and user-friendly
- molecular: required trained personnel
Lateral Flow Assay vs. Molecular Assay
Cost
- lateral: relatively inexpensive
- molecular: relatively expensive
Lateral Flow Assay vs. Molecular Assay
Examples
- lateral: COVID-19 rapid antigen test, pregnancy test
- molecular: ID now (influenza, strep, RSV)
What is sensitivity?
ability of a test to correctly identify individuals with the condition – true positives (TP)
- ie. highly sensitive HIV test correctly detects 98% of HIV-positive individuals – meaning, 98 out of 100 people with HIV will be correctly identified as HIV+, however, 2 out of 100 may receive a false negative
What is specificity?
ability of a test to correctly identify individuals without the disease (true negatives)
- ie. highly specific cholesterol test correctly identifies 95% of healthy individuals without high cholesterol – meaning, that 95 out of 100 people without the condition will correctly receive a negative result, however 5 out of those 100 people may receive a false positive result
What is prevalence?
proportion of individuals in a population having a disease at a particular point in time – equivalent to the pre-test probability
- accuracy of a test in determining the pre-test probability depends on the prevalence of the condition in the population being tested
- when the condition is common, false positive results are more likely
- when the condition is less common, false negative results are more likely
- prevalence estimates may be available from health department surveillance data or the literature
What is the likelihood ratio?
calculated from the sensitivity and specificity of a test and take different prevalences into account
- positive likelihood ratio (LR+): measures the effect of a positive test on the probability of a disease
- negative Likelihood ratio (LR-): measures the effect of a negative test on the probability of a disease
- can be obtained from literature for certain devices, or can be calculated from sensitivity and specificity
- LR+ = sensitivity / (1 - specificity)
- LR- = (1 - sensitivity) / specificity
- LR = 1 = no change in the likelihood of the condition
- LR > 1 = the more likely the condition
- LR <1 = the less likely the condition
What are the conditions/factors that may influence POCT results? (5)
- medical conditions – ie. patients with anemia may not have accurate A1c results
- medications/drugs – ie. vitamin C may falsely raise glucose readings in certain continuous glucose monitoring systems
- other substances – ie. nasal swabs with high level of mucin contaminant may interfere with antigen detection
- population – tests generally have an intended use or target population (ie. covid-19 rapid antigen test should generally only be used in symptomatic individuals)
- asymptomatic carriers – ie. devices which amplify GAS nucleic acids are not able to differentiate between active infection and asymptomatic carriers
How should you counsel a positive test result?
- counselling and education about the positive result and condition
- refer for confirmatory testing, if required
- refer patient to their doctor for further assessment if needed
- if appropriate, fax the doctor with treatment recommendation
- treatment recommendation (OTC or prescribe) if within pharmacists’ scope
- public health reporting may be required for certain diseases
How should you counsel a negative test result?
- counselling and education about the negative result and accuracy and limitations of the test
- reinforce precautions and prevention if appropriate – ie. vaccination, following infection control procedures (washing hands, self-isolating)
- refer for further assessment if required, such as high-risk patients
What are some general counselling points?
- provide disease education as appropriate
- provide non-pharmacological measures as needed
- direct patients to necessary healthcare resources
- follow-up care to monitor patient’s health status
What are CLIA-waived tests?
tests that are simple to conduct and with little risk of error and therefore can be performed by sites – ie. pharmacies that have obtained a CLIA waiver
- Clinical Laboratory Improvement Amendments (CLIA) in United States applies to laboratory facilities testing human specimens
- ‘CLIA waived’ is often listed on manufactures product information
What is the Canadian regulation for POCTs?
all devices must be approved for use by Health Canada
- however, Class 1 medical devices, which are non-invasive, do not require a medical device license
What are the POCT policies set by the Ministry of Health BC?
has ‘community-based point-of-care testing policy’ to guide implementation of quality POCT service in the absence of specific POCT standards by colleges
- safety and training – ongoing training and skill maintenance, written procedures available
- care environments – privacy, cultural safety
- reporting results – written procedures, data collection privacy
- follow-up care – outline plan or refer patients to other HCPs
- proficiency and quality control – to ensure reliable and accurate test results
- device and equipment – Health Canada approved, regular evaluation is recommended
- specimen collection – should align with manufacturer recommendations, written procedures
- education – practice within their scope
