IMM 16: Introduction to Point of Care Testing

Question 1

What is point-of-care testing (POCT)?

Answer 1

form of testing in which the analysis is performed where the healthcare is provided close to or near the patient

Question 2

What are the characteristics of POCT? (4)

Answer 2

• 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

Question 3

What are the benefits of POCT? (4)

Answer 3

• 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

Question 4

What are the drawbacks of POCT? (2)

Answer 4

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

Question 5

What are the 2 types of point-of-care devices?

Answer 5

• lateral flow immunoassay
• molecular assay

Question 6

What are immunoassays?

Answer 6

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)

Question 7

What are lateral flow immunoassays?

Answer 7

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

Question 8

What are molecular assays?

Answer 8

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

Question 9

Lateral Flow Assay vs. Molecular Assay

Principle

Answer 9

• lateral: capillary action
• molecular: nucleic acid amplification

Question 10

Lateral Flow Assay vs. Molecular Assay

Equipment

Answer 10

• lateral: no external equipment
• molecular: required specialized equipment (PCR machine)

Question 11

Lateral Flow Assay vs. Molecular Assay

Sensitivity and Specificity

Answer 11

• lateral: moderate (usually)
• molecular: relatively high (usually)

Question 12

Lateral Flow Assay vs. Molecular Assay

Multiplexing

Answer 12

• lateral: limited – usually detects a single analyte
• molecular: can detect multiple analytes simultaneously

Question 13

Lateral Flow Assay vs. Molecular Assay

Complexity of Use

Answer 13

• lateral: simple and user-friendly
• molecular: required trained personnel

Question 14

Lateral Flow Assay vs. Molecular Assay

Cost

Answer 14

• lateral: relatively inexpensive
• molecular: relatively expensive

Question 15

Lateral Flow Assay vs. Molecular Assay

Examples

Answer 15

• lateral: COVID-19 rapid antigen test, pregnancy test
• molecular: ID now (influenza, strep, RSV)

Question 16

What is sensitivity?

Answer 16

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

Question 17

What is specificity?

Answer 17

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

Question 18

What is prevalence?

Answer 18

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

Question 19

What is the likelihood ratio?

Answer 19

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

Question 20

What are the conditions/factors that may influence POCT results? (5)

Answer 20

• 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

Question 21

How should you counsel a positive test result?

Answer 21

• 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

Question 22

How should you counsel a negative test result?

Answer 22

• 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

Question 23

What are some general counselling points?

Answer 23

• 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

Question 24

What are CLIA-waived tests?

Answer 24

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

Question 25

What is the Canadian regulation for POCTs?

Answer 25

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

Question 26

What are the POCT policies set by the Ministry of Health BC?

Answer 26

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