Point-of-Care Testing

Specimen Requirements and Procedure

There are 3 primary stages in the POCT process: pre-analytical, analytical, and post-analytical. The pre-analytical phase occurs before running the POCT on a sample and involves collection, transport, preparation, and loading. The analytical phase is the stage in which the actual testing sequence of a POCT is conducted. The post-analytical phase begins when testing is complete, and an obtained result is available. During this phase, the obtained result from the test is communicated for treatment through the electronic medical record (EMR) or written or verbal instructions directly to the treatment team. The post-analytical step is also when "so-called" critical values, which are values that deviate significantly from normal reference values and indicate a pathological process. The resultant values are interpreted during this step to guide appropriate actions and interventions.

Specimen collection and handling are critical components of POCT since testing is performed directly on the collected specimen.[11] The pre-analytical phase of specimen collection and handling is crucial and represents the most critical controllable variable in POCT. Adhering to personnel regulations, appropriately preparing patient and specimen collection containers (including fixatives or special media), and ensuring compliance with patient and specimen identification requirements are essential for effective collection and handling. Additionally, accurate clinical documentation and proper specimen storage are necessary to maintain the integrity, accuracy, and safety of the testing process.

Adhering to the manufacturer's instructions for use (MIFU) or package insert is crucial in ensuring accurate testing in POCT. This is particularly important regarding sample preparation, including factors like centrifugation time, and may vary between manufacturers and sample types. Professionals performing POCT should carefully follow the specific instructions provided by the manufacturer for each apparatus used. Professionals prefer some POCT methods that utilize whole blood as they eliminate the need for additional processing steps or centrifugation. Additionally, sample collection containers must be within the manufacturer's date stamp to maintain the quality and reliability of the testing process. 

POCTs are more susceptible to interfering substances and have a narrow margin of error due to smaller sample sizes compared to conventional laboratory tests.

Proper technique is crucial when drawing samples, particularly when accessing a central line.[12] This involves flushing the line with heparin and discarding at least twice the volume of the line (2 to 5 mL) before sample collection. It is recommended to wait at least 15 minutes after a blood transfusion before drawing a sample for POCT.

Samples collected for blood gas analysis are susceptible to changes in oxygen partial pressure. Therefore, it is crucial to maintain anaerobic conditions during sample collection to ensure accurate laboratory values.[13] Controlling factors such as removing all air bubbles from a sample, using a plastic syringe for collection, and the time and temperature of sample storage (if storage is required) before analysis are crucial for accurate blood gas analysis.

Diagnostic Tests

POCT testing devices are classified based on the testing modality and the test size.[9] Test size in POCT spans a wide range, and ongoing research focuses on miniaturization. Handheld POCT devices, including dipsticks and meters like glucometers, represent smaller-scale options within this spectrum.

The most recent iterations of these devices feature cartridges that enable multiple tests, including whole blood analysis for cardiac markers, blood gases, and various hematologic and endocrine analytes. On the larger end of this spectrum, there are larger benchtop POCT units that require dedicated space near a patient to qualify as POC.

Many of these benchtop POCT units are equipped with multiple testing types and modalities, allowing for a wide range of diagnostic tests to be performed within a single device. Common examples of tests performed on benchtop POCT units include hemoglobin A1c, C-reactive protein (CRP), and general chemistry analytes. The demand for smaller and more precise benchtop POCT devices has been a significant catalyst for innovation in reducing the size of these instruments. Advancements in technology and engineering have enabled the development of compact and highly accurate benchtop POCT units.

Testing Strips and Lateral-flow Testing

POCT encompasses a wide range of testing modalities tailored to specific applications. The most basic POCT takes advantage of an interaction between an analyte and a substance, usually impregnated or contained, so that a sample can be added or mixed in a controlled manner.[14] An example is using test strips (eg, urine test strips). These strips are generally dried, porous matrices with impregnated carrier elements that interact with the analyte(s) when exposed. The interaction between the analyte and the testing reagents often involves a chemical reaction that produces a color change. This color change can be interpreted as a binary value indicating the presence or absence of the analyte or as an indication of the analyte concentration using a scale (eg, trace protein, 1+, 2+, 3+).

A more complex approach to POCT is lateral-flow testing. This type of diagnostic testing utilizes a layer of supporting material, such as porous paper of cellulose fiber filters or woven meshes. The supporting material contains capillary beds to whisk fluid samples to location(s) on the support material with substances that react with measured analytes in the sample. A well-known example is the at-home pregnancy test, which commonly utilizes an immunoassay to detect the presence of human chorionic gonadotropin (hCG, specifically beta-hCG) in urine.

Urine is exposed to one end of the supporting material in the test device; capillary beds then move the urine through the supporting material to specific sites that react with beta-hCG. This configuration commonly has 2 lines of reactive material, one that serves as the control and another that indicates a binary yes or no indication. The test is positive if both lines (also known as stripes) appear or change color and negative if only the control line is visible. Failure of the control line to appear indicates an invalid or faulty test, which could result from a manufacturing defect, damage, or expired test.

In many instances, POCTs that utilize simple test strips or lateral-flow testing provide qualitative or semiquantitative results and do not provide precise information regarding the specific concentration of the measured analyte.

Immunoassays

POCT testing that utilizes immunoassays relies on antibodies to bind to a specific target when the concentration exceeds a certain threshold.[14] Targets in immunoassays for POCT can encompass a wide range of substances, including proteins, drugs, and pathogens. POCTs are available in various formats, including both individual tests and platforms with multiple built-in tests. In general, testing platforms require more space and greater expertise and training; this generally scales with the number of tests offered.

Deciding between using a testing platform versus an individual test or even utilizing an array of individual tests depends on the workflow and throughput required. Higher sample volume can often be accommodated more effectively using a POCT testing platform. However, the suitability of a specific platform depends on the testing type and the platform's capabilities.

One subset of immunoassays is the direct assay, which provides a straightforward method for detecting an analyte. In a direct immunoassay, the analyte of interest is directly bound by an antibody that specifically recognizes and binds to it. This binding event is then detected, typically through fluorescence, by an optical sensor. The fluorescence signal indicates the presence and quantity of the analyte in the sample.

In situations where a direct assay is not feasible, competitive immunoassays can be employed. These assays utilize the principle of competitive binding between a measurable, secondary analyte and the target analyte. As the test antibodies bind to more of the primary analyte, the level of bound, measurable analyte decreases due to competitive binding; this allows for the determination of the primary analyte's concentration. Unlike simple test strip-based POCT, immunoassay POCT provides quantitative information for specific analytes.[15][16]

Antigen-based Testing

POCT, which involves the detection of known antigens or antibodies specific to a particular disease or disease state, has been widely employed as a common practice in healthcare.[17] Immunoassay-based POCT is commonly used to rapidly detect group A Streptococcus, mononucleosis, and influenza A and B. These tests utilize immunoassays that bind specific antigens or antibodies. Immunosay-based POCT offers a fast turnaround time (TAT) but may have lower sensitivities and specificities compared to traditional laboratory and molecular testing methods.

Molecular POCT

The demand for molecular POCT with high sensitivity and specificity and a relatively short turnaround time (although longer than antigen-based testing) spurred its development.[17] This form of testing detects DNA or RNA sequences indicative of the presence of disease. Nucleic acid amplification testing (NAAT) is used to identify DNA or RNA in small test samples. The nucleic acids of interest are replicated to increase their concentration (ie, amplify them) so they are easier to detect.[18]

There are various forms of this testing, including reverse transcription polymerase chain reaction (RT-PCR) and isothermal amplification methods such as nicking endonuclease amplification reaction (NEAR) and transcription-mediated amplification (TMA).

It is important to note that while molecular POCTs often have higher sensitivities and specificities compared to antigen-based POCTs, this is not always the case. Additionally, the increased sensitivity and specificity provided by this POCT modality may not always be clinically beneficial, as the detection of an analyte does not necessarily correlate with a specific disease state or the need for treatment (eg, the presence of a small amount of Clostridium difficile in a patient's stool does not always indicate the need for treatment of a C difficile infection.[19]

Testing Procedures

Testing procedures for POCT vary based on the specific manufacturer, test, and sample type. For accurate results in most POCT units, setting up and calibrating the specific test before use properly is essential. Following the manufacturer's instructions for use (MIFU) or package insert for each POCT apparatus is crucial in achieving accurate testing.

General POCT Testing Procedures

1. A sample is obtained for analysis. This could be a drop of blood for blood glucose concentration via a glucometer or urine for beta-hCG. Various requirements regarding the patient's state, the specimen's state, and the preparation needed for accurate testing exist. This is discussed in further detail in both the "Specimen Requirements and Procedures" and "Quality Control and Lab Safety" sections.[20]
2. The sample is applied to the POCT device. Immediately before this step, a reagent may facilitate accurate testing. For example, some POCT units for COVID-19 require samples obtained via nasopharyngeal or oropharyngeal swabs to be placed in a reagent solution to facilitate the transfer of antigen into the solution.[21] This allows for the distribution of the antigen throughout the solution and increases test accuracy. In some types of POCT, the sample can be directly applied to the device, which typically includes a disposable cartridge for analyzing the analyte. This disposable cartridge can be disposed of after use, reducing the risk of cross-contamination.
3. Once the test is performed, the result is obtained and can be directly transferred to the patient's electronic medical records (EMR) if the POCT device is integrated or interfaced with the EMR system.

Interfering Factors

Due to the portable nature of POCT, the reagents, tests, and samples are often exposed to conditions that may differ from those in a traditional laboratory setting. Humidity, temperature, time to testing, and oxygen content can fluctuate more in the POCT setting than in the conventional laboratory environment. Most interfering factors with POCT occur before the test is run (pre-analytical phase).[22]

Errors in the pre-analytical phase can occur during patient identification and in the specimen's identification, collection, handling, processing, transport, and storage. These errors may include hemolysis, clotting, underfilling or overfilling a specimen container, improperly securing specimen containers before transport, prolonged tourniquet time, and changes in the sample concentration (eg, during aliquoting).

Notably, the detection of hemolysis in POCT using whole blood samples (including fingerstick tests) is challenging.[23] Errors during specimen transfer and loading, such as bubbles, microclots, and gross clotting, can occur, especially if the procedure is not followed appropriately or lacks oversight. Increased time to testing can interfere with POCT, as observed in the case of blood glucose testing in whole blood. Adequate training is a critical component of POCT, as pre-analytical errors have an inverse association with test operator experience.

Other interfering factors may be directly related to the patient's physical state. For instance, elevated biotin intake (eg, from vitamin supplementation) can interfere with certain immunoassays, such as human immunodeficiency virus (HIV) POCT.[24] This stems from the interaction between biotin and streptavidin in the assay. Affected assays include but are not limited to pancreatic, prostate, and ovarian cancer POCT and pituitary and thyroid function tests. Reading the MIFU or package insert is essential for POCT, as certain drugs can interfere with the test and affect accuracy. Some POC glucose monitoring systems may report erroneously elevated glucose levels in patients treated with maltose, icodextrin, galactose, or xylose.[25]

Hemolysis, icterus, and lipemia may result in inaccurate or incalculable results. Potassium measurements are susceptible to this error. Testing in conventional laboratories often includes a step to determine the serum index in addition to testing for a specific analyte.[13]

Collectively, these indices are often referred to as hemoglobin (H), lipemia (L), and icterus (I), or HIL, indices.[26] These are obtained most typically via spectrophotometric assessment. However, in POCT, hemolysis, icterus, and lipemia can only be detected by visual inspection of a centrifuged aliquot of the sample. High turbidity or an excess of an untested component in a sample, such as in whole blood samples with high concentrations of lipids, may also skew test results or result in an error.[27]

Ways to resolve these errors vary based on the devices used and MIFU; in some cases, dilution can resolve sample errors related to excess bilirubin, and ultracentrifugation can help fix errors related to excess lipids. Patients with reduced or compromised peripheral circulation, as seen in patients with sepsis, shock, or diabetic ketoacidosis, may have inadequate capillary blood samples.[28]

Results, Reporting, and Critical Findings

Results

POCT results that yield critical values are typically acted upon promptly, leading to potential changes in clinical management.[29] This could be as benign as a reflexive beta-hCG taken after a positive urine pregnancy test in the emergency department. Therefore it is essential to record the result and action taken whenever a critical value result is obtained.

Critical values, unlike urgent or STAT tests, are defined as test results that significantly deviate from the established normal range, irrespective of the patient's condition. STAT or urgent tests are designated as such by the individual ordering the test, and therefore prior knowledge of the patient's status is generally needed.

Reporting Critical Findings

Critical values should be treated as reportable events, even if previous critical values are already known for a particular patient.[29] The critical value reporting policy should be consistently followed for each instance of obtaining a critical value. Deviation from this policy should only be considered in exceptional cases supported by sufficient evidence, such as obvious testing errors or pre-analytical errors, justifying the decision to ignore the critical value.

Clinical Significance

Because of its quick turnaround time and place in various workflows, POCT has great clinical significance; the information gleaned from POCT is used routinely to guide patient treatment and management. POCT offers several advantages compared to conventional lab testing, with benefits that vary depending on the specific setting in which the testing is conducted.[20][30] 

POCT, performed near patients, typically enhances patient satisfaction and experience by eliminating the need for sample transport, reducing turnaround time (TAT), and avoiding procedure delays. POCT enables patient counseling, prevents unnecessary treatment escalation, and provides rapid results outside the hospital setting, such as in outpatient testing, to avoid hospitalization or confirm viral illness, thereby reducing antibiotic use.

POCT offers advantages in different test types. For example, fingerstick blood glucose measurements can replace venipuncture for serum testing, requiring less training and posing lower risks of complications and infection, thereby improving patient experience and safety.[31] In specific patient populations like neonates or those prone to increased blood loss from phlebotomy, the smaller sample volume required for POCT is advantageous.

POCT has some drawbacks, primarily related to the potential for less accurate results than traditional laboratory testing. This can be attributed to variable personnel training and control over pre-analytical, analytical, and post-analytical variables, which can be better managed in a laboratory setting. POCT can be more costly on a per-test basis compared to traditional laboratory testing, primarily due to the single-use nature of most POCT devices, which adds to the overall expenses.[32] Documentation challenges and potential errors in recording or documenting POCT results can occur due to varying personnel practices and workflow processes within a clinical setting.

Quality Control and Lab Safety

All facilities or sites in the US that conduct diagnostic testing or medical treatment using human specimens are subject to regulation under the Clinical Laboratory Improvement Amendments of 1988 (CLIA 88).[33] CLIA designates tests that are simple to perform and have a low risk of producing incorrect results as waived tests. Most point-of-care tests are waived; however, some are non-waived and are subcategorized as moderately complex tests. Waived tests are excluded from competency assessment requirements per the Centers for Medicare & Medicaid (CMS), though various state and accrediting bodies may still keep this requirement in place. Non-waived tests are subject to specific quality standards, including proficiency testing, quality control (QC), and personnel requirements.

The successful development of effective quality control for laboratory testing requires using verified controls to ensure that a POCT is functioning as expected and will yield accurate results.[34] QC material contains the analytes of known concentrations. The frequency of quality control testing should be determined based on the complexity and risks associated with the test in question. For high-throughput devices, QC should be run at least once daily. New lots of reagents are tested with these controls before being used to run patient samples. Additionally, such controls allow for troubleshooting among different individual tests and operators. The internal QC documentation, which includes the date and time of testing, lot number, and user identification, is essential for effective QC.

Patient testing must be associated with the specific lot numbers for all products used for POCT, including the device, reagents, and sample collection materials. Many POCTs contain electronic records of such information, though historically, this information has been recorded in a logbook. Significant variables to ensure ongoing quality assurance include expiration dates for reagents, controls, and sample collection materials, proper storage and management of all materials involved in POCT, and proper establishment of acceptable ranges for test values.[34]

Due to the decentralized nature of POCT, effective personnel management on an individual level is critical. Ideally, every person that runs POCT would be competent with the safe and accurate operation of each POCT. Many larger institutions implement electronic training modules and regularly track individual competency for POCT, in line with the requirements set by accreditation bodies such as CLIA.  Accreditation bodies, including CLIA, require 6 main competency elements: 1) direct observation of test operation, 2) monitoring of both recording and reporting of test results, 3) review of intermediate steps of POCT (test results, QC records), 4) direct observation of preventative maintenance and function check performance, 5) assessment of test performance using specimens previously analyzed, and 6) assessment of personnel problem-solving skills.[35]

Lab Safety

Lab safety is a critical component of effective POCT for the patient, the sample collector, and the person that runs the POCT. One unique aspect of POCT is that the same person often carries the collection and test execution. Because of this, care must be taken so that task overload and errors in collection, transport, and analysis do not occur. Contamination of a POCT can impact multiple patients and operators, especially if the POCT in question is frequently used. The proper use of personal protective equipment (PPE) and corresponding protocols are critical for the protection of personnel and the accuracy of testing.[36]

The rules of universal precaution should be applied to POCT, and protective measures such as splash shields and biosafety cabinets should be employed based on manufacturer and government agency guidelines. Recommendations for competency elements in POCT vary depending on the type of test and the samples collected. For example, POC molecular testing for nasal swabs, such as in the case of COVID-19 testing, generally requires specific personal protective equipment (PPE) to prevent exposure to airborne pathogens during testing.[37][38]

Lab safety also applies to adequately disposing of samples and waste after completing POCT.[39] All laws, regulations, and accreditation requirements for medical waste disposal must be followed. After sample collection via venipuncture, the needle must be covered; fingerstick lancets must be single-use. All needles and lancets must be appropriately disposed of in a hazardous waste container designated for needles (a sharps container).

Proper disposal of POCT swabs depends on local and facility waste disposal procedures. However, a general guideline is that swabs used for POCT that remove the sample from the swab (for example, POCT that wash or require swirling of the swab in fluid) do not require disposal in a designated biohazard receptacle.[8] Swabs contaminated with biological material must be disposed of in a proper biohazard bag. Finally, when appropriate, the proper removal or covering of protected health information (PHI) must be considered on all samples and sample containers. This applies to both physical and electronic information.

Enhancing Healthcare Team Outcomes

POCT occurs in a wide range of clinical settings, including inpatient, outpatient, and non-clinical settings, such as homes, airports, and cruise ships. The COVID-19 pandemic significantly increased the use of POCT, with billions of tests rapidly developed and distributed worldwide to help control the spread of the virus and facilitate the timely identification of infected individuals.

Various healthcare professionals, including physicians, nurses, medical technologists, and trained personnel, perform point-of-care testing to obtain immediate results that inform and guide clinical patient management decisions. Due to the diverse range of healthcare professionals and workflows involved in POCT, providing adequate training, facilitating interprofessional communication, and establishing clear guidance to ensure accurate testing and effective relay of test results to the treatment team is crucial.

Interprofessional committees dedicated to the implementation, execution, and continuous quality management of POCT have been recommended as they play a crucial role in enhancing the quality of healthcare delivery within entire health systems. These committees promote collaboration, standardization, and effective oversight of POCT practices, ultimately benefiting patient care.[40] [Level 1] Various randomized clinical trials using POCT demonstrate improved patient outcomes compared to conventional laboratory testing.[41][42][43] [Level 1]

One of the advantages of point-of-care testing (POCT) is the ability to update the patient's electronic medical record (EMR) with real-time test results. This enables the interprofessional team to access the most accurate and updated data, leading to a more comprehensive and functional clinical picture. As a result, healthcare professionals, such as pharmacists, can make more efficient and informed decisions regarding medication dosing, such as adjusting warfarin or aminoglycoside dosages, based on the patient's current status.

Using POCT facilitates closer monitoring of a patient's condition by nurses. With real-time access to test results through the EMR, nurses can promptly detect any significant changes and alert the attending physician or appropriate healthcare professionals for clinical intervention. Interprofessional coordination and collaboration among physicians, advanced practice practitioners, specialists, pharmacists, lab technicians, and nurses are crucial in utilizing POCT effectively and ultimately enhancing patient outcomes. By working together, the healthcare team can make well-informed decisions and provide timely and targeted care based on the POCT results [Level 5]