Part 2. Types of POC systems. Basic specifications.
Types of POC devices
Researchers classify POC-systems according to different parameters: application, operating principle, device, etc., because at the moment there is a large variety of rapid tests which use unique diagnostic methods. The authors of the article Existing and Emerging Technologies for Point-of-Care Testing conditionally classify POC devices into two categories:
Small, portable devices that ensure qualitative or quantitative determination of the tested substances
The user can simply apply the test sample directly onto the POC device without the need for containers, labeling or transportation.
These devices are also used in blood gas testing. Patients can use these devices on their own or with the support of a doctor.
Some examples of these devices:
a) Test strips for urine or blood tests
Thin plastic sticks with strips of chemicals on them are placed in the test sample. Chemical elements on the sticks change color if certain substances are present in the sample or if the levels of any substances are higher than normal.
|Such tests determine levels of acidity as well as the content and concentration of
They can also detect signs of infection, the presence of blood in urine, and blood gas composition.
These devices are based on the use of chromatographic membranes and the principles of immunochromatographic analysis.
Immunostrips are immunosensors in which the recognizing agent is an antibody. It binds to the test substance (analyte/antigen), which can be detected by spectrophotometric techniques. They have been created in a variety of formats, the first of which was a design using cells with a porous matrix.
|The are used to detect and measure
You can read more about how immunostrips work in our article “How Most Test Strips Work. Immunochromatographic assay”.
A glucometer is a small device that measures the sugar level in capillary or venous blood. One drop of biomaterial is sufficient to perform the analysis. The sample obtained is applied to special consumables from which the meter reads information. The measurement result is displayed on the screen of the device.,
|The glucometer is designed for
You can read more about how glucometers work in our article “How Glucometers Work”.
d) POC-tests for hemostasis evaluation
The hemostasis system is a biological system in the body whose function is to preserve the liquid state of the blood, stop bleeding when there is damage to the walls of blood vessels and dissolve blood clots that have fulfilled their function.
These POC devices perform a coagulogram (hemostasiogram) – a comprehensive hematological study aimed at assessing the state of the hemostasis system (blood clotting), or blood clotting indicators.
The hemostasis system includes blood cells (platelets) and specific substances (clotting factors) dissolved in blood plasma and contained in platelets. When the integrity of the vessel wall is compromised, the clotting system is activated and a blood clot is formed to prevent blood loss.
|Parameters studied in the screening coagulogram:
These values are basic and allow the evaluation of all clotting pathways.
e) Combined cartridges.
Such POC tests can measure multiple parameters of the same sample. After placing a small whole blood sample, the cartridge is inserted into the reader for measurement. The cartridge uses thin-film sensors combined with microfluidics and is available in different formats for different analytes.
Larger, frequently tabletop devices which are essentially laboratory devices, but smaller and more convenient to use
a) Devices that examine urine composition and characteristics
b) Critical condition analyzers;
According to the MES Dictionary of Terms,
a critical condition is the condition of the affected (patient), which is characterized by severe disorder of the vital body systems (primarily cardiovascular and respiratory), requiring emergency recovery (partial or complete replacement) with resuscitation measures.
Various POC devices are used to assess this condition.
c) Small hematologic and immunologic analyzers
Hematology tests are laboratory tests that provide information on the quantitative and qualitative composition of blood, and determine the number of antigens, antibodies. They allow the detection of many negative changes in the body, narrowing down the diagnostic search and choosing the best treatment regimen.
Any modern hematology analyzer is a set of mechanical, hydraulic, pneumatic and measuring systems. The hydraulic and pneumatic systems are responsible for retrieving reagents from the tanks, delivering the sample and reagents within the analyzer, and removing waste outside the analyzer. The mechanical system is responsible for moving the sampler or autofeeder, depending on the model, as well as controlling the slide valve and various kinds of agitators.
Hematology analyzers determine the following parameters:
as well as the following erythrocyte parameters: mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, hematocrit.
Different types of analyzers determine the leukocyte and platelet spectrum, and their subpopulations. In addition, histograms (red blood cell, white blood cell, and platelet volume distribution functions) can be obtained.
The range of use of hematological and immunological indicators is wide :
Indicators are also used in
Also, hematologic and immunologic parameters are used to screen for
Any deviation from the normal hematologic and immunologic reference range is indicative of a number of human diseases and therefore represents important parameters for diagnosing and monitoring the patient’s condition.
d) PCR instrumentation
PCR is performed in an amplifier, a device that periodically cools down and heats up test tubes, usually to an accuracy of at least 0.1 °C. Modern amplifiers allow the creation of sophisticated programs, including hot start, Touchdown PCR, and ensure the subsequent storage of amplified molecules at 4 °C. Instruments equipped with a fluorescence detector are available for real-time PCR. There are also tools with an automatic lid and a compartment for microplates, allowing them to be built into automated systems.
What is the PCR test for?
The PCR method allows you to determine the presence of a pathogen, even if only a few molecules of pathogen DNA are present in the sample.
PCR makes it possible to diagnose the presence of slow-growing pathogens without resorting to time-consuming microbiological methods, which is especially relevant in gynecology and urology for the diagnosis of urogenital sexually transmitted infections (STIs).
Also, this method is used to diagnose viral infections, such as
Method sensitivity significantly exceeds that of immunochemical and microbiological methods, and the principle of the method makes it possible to diagnose the presence of infections with significant antigenic variability.
|The authors also highlight the features of large intensive care analyzers that reduce the risk of errors and simplify use.||Key aspects that need to be given special attention when developing POC devices. (In some test systems, not all of the listed aspects are present, for example, in test strips due to their “simplicity”)|
According to the aforementioned article Existing and Emerging Technologies for Point-of-Care Testing, the developed test systems must meet the following technical requirements:
- Ease of use;
- Reagents and consumables are reliable for storage and use;
- Results must be equivalent to the laboratory method;
- The device, together with the appropriate reagents and consumables, is safe to use.
The article also notes that due to the great potential of POC devices, the World Health Organization has developed the following guidelines for those involved in the development of test systems for the detection of sexually transmitted infections (HIV, Chlamydia, etc.):
- Accessibility – for those at risk of infection;
- High sensitivity – minimum number of false negative results;
- Specificity – minimum number of false positive results;
- Ease of use – minimum number of actions that need to be performed during testing;
- Fast and reliable – short testing time and no need to store samples in the refrigerator;
- Lack of complex equipment – the user does not have to deal with complex equipment;
- Deliverability – delivery of test systems to the end user is ensured.
A separate place in the classification of test systems is occupied by a lab-on-a-chip. According to the definition:
Lab-on-a-chip or micro total analysis systems, LOC; µTAS), or complete analysis microsystems, is a miniature device that allows one or more multi-stage (bio)chemical processes to be carried out on a single chip with an area from several mm2 to several cm2 and uses micro- or nanoscopic amounts of samples for sample preparation and reactions.
You can learn more about lab-on-a-chip technology in our article “Lab-on-a-chip”.
In this article, we looked at the most famous types of POC systems. All of them are designed for accelerated testing of patient samples. To some extent, they are the future of analyzers, because POC devices greatly simplify the process of analyzing analytes.
- Prothrombin time (PTT) is the time it takes for a blood clot to form. This indicator allows you to evaluate the work of the blood coagulation system.
- International Normalized Ratio (INR): Essentially, this is also the definition of PTT, but using a specific standardized tissue factor (clotting factor).
- Existing and Emerging Technologies for Point-of-Care Testing (nih.gov) ↑
- How to use a glucometer from MedMag SPb – MedMag SPb (medmagspb.ru) ↑
- Glucometer — Wikipedia (wikipedia.org) ↑
- Complete blood count (CBC): interpreting the results, reference value tables (zn48.ru) ↑
- Hematological analyzer — Wikipedia (wikipedia.org) ↑
- IMMUNOLOGICAL INDICATORS, HEMATOLOGY TESTS is the topic of the scientific article on health sciences, read the text of the research paper for free in the electronic library CyberLeninka (cyberleninka.ru) ↑
- Polymerase chain reaction — Wikipedia (wikipedia.org) ↑
- PCR: what is it?Diagnosis of infectious diseases by polymerase chain reaction (invitro.ru) ↑
- Lab-on-a-chip — Wikipedia (wikipedia.org) ↑
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