Point-of-Care Testing





Introduction


Point-of-care (POC) testing is a term used to describe diagnostic testing that is performed in the patient’s unit rather than in the hospital’s central lab or outside reference lab. POC testing may be done on blood, urine, swabs from mucosal surfaces, or saliva. In the emergency department (ED), POC testing is typically performed by both ED technicians (EDTs) and nurses. In some jurisdictions, emergency medical services providers use POC tests in prehospital settings. Most hospitals have developed a rigorous quality process for their POC testing programs.


Comparisons With Laboratory Tests


There are pros and cons to POC tests. Point-of-care tests have fewer steps and thus a shorter time between test order and results compared with central lab-performed tests, and patient comfort may be improved by using a smaller sample for testing. The samples required to run POC blood testing are typically no more than 2 to 3 drops of blood. Many POC testing devices also bundle several types of lab tests together so users can obtain multiple results with one sample.


However, decreased accuracy is a potential drawback of POC testing compared with traditional laboratory tests, particularly if the analyte measured is significantly abnormal. For example, when measuring blood glucose levels, a POC test might report a sample as “high,” whereas the central lab would report a specific value. Accuracy and reliability vary depending on the type of test. Advantages and disadvantages of POC testing are highlighted in Table 7.1 .



Table 7.1

Advantages and Disadvantages of Point-of-Care Testing






















Advantages Disadvantages
Quicker results Increased training for clinical staff
Fewer steps in specimen processing Increased cost per test
Smaller fluid sample required Decreased accuracy/reliability of test results
Limited types of tests available
Decreased patient length of stay Space requirements for storage and testing


It is uncertain whether POC testing decreases medical errors. The simpler process for POC tests may also reduce potential error, such as lost samples and delays in retrieving results. However, in some cases results from POC testing must be manually entered into the facility’s database, which may increase the risk of inaccurate results.


Point-of-Care Testing Operation


Although there are various techniques and devices used to perform POC testing on patients, most blood tests are performed on a handheld blood analyzer, such as the Abbott i-STAT device. This device uses cartridges preloaded with the desired tests. The cartridges must be stored at room temperature and they have a specific expiration date. After obtaining a blood sample from a patient, a trained user can follow the prompts on the device to perform the test(s). Fig. 7.1 shows how to operate a typical POC machine (See , Using and ISTAT Machine).




Fig. 7.1


How to use a handheld blood analyzer.

(A) An i-STAT machine, a common brand of handheld blood analyzer. The arrow indicates the slot where the cartridge will be inserted. (B) Starting up the machine. (C) Scan or enter the operator ID, commonly assigned by a hospital or healthcare facility. (D) Scan or enter the patient ID, commonly found on a patient’s hospital armband. (E) Scan or enter the cartridge lot number. (F) Package of an i-STAT CG4+ cartridge, one type of chemistry panel. The cartridge lot number is included on the package. A sticker placed by the laboratory indicates the cartridge expiration date. (G) After entering the appropriate information, the machine is ready for the insertion of a properly filled cartridge. (H) An i-STAT CG4+ cartridge. The arrows indicate the well for blood insertion, the fill line indicating when to stop filling the well, and the cartridge door, which the user closes over the well once the cartridge is properly filled. The filled cartridge is inserted in the orientation shown into the cartridge slot, shown in (A). The machine will lock the cartridge in place until the test is completed.


Using a Handheld Blood Analyzer




  • 1.

    Sanitize hands and don gloves/appropriate personal protective equipment (PPE).


  • 2.

    Draw the patient’s blood into a syringe and attach a blunt-tip needle.


  • 3.

    Turn on the device (see Fig. 7.1B ).


  • 4.

    Scan and/or manually enter user, patient, and cartridge information for the relevant test, and then place the device on a level surface (see Fig. 7.1C–F ).


  • 5.

    Open the desired cartridge.


  • 6.

    Waste a few drops of blood from the syringe to ensure the cartridge sample will not contain air bubbles.


  • 7.

    Fill the cartridge well slowly with blood using the syringe until the blood level reaches the fill line indicated on the cartridge (see Fig. 7.1H ).


  • 8.

    Shut the cartridge door gently and insert it into the slot of the analyzer (see Fig. 7.1G–H ). The device will then proceed with running the test; the device screen may indicate “cartridge locked” with the time to results. Leave the device undisturbed on a level surface until the test is complete.


  • 9.

    After the results display, dispose of the used cartridge and waste materials appropriately.


  • 10.

    Use the buttons as directed on the device to indicate the type of blood sample used (arterial vs. venous), and enter “comment codes” if any critical values indicate that the results should be reported directly to the provider team.


  • 11.

    Place the blood analyzer in its appropriate docking station to transmit results and/or document the result manually in the patient’s chart. Results can also be printed if needed.


  • 12.

    Remove and dispose of gloves.


  • 13.

    Sanitize hands.



Types of Point-of-Care Tests


Cardiac


See Table 7.2 for a summary of indications for cardiac POC testing.



Table 7.2

Cardiac Point-of-Care Tests
















Test Indications Mode of Collection
Troponin Acute Coronary Syndrome (Heart Attack) Symptoms:


  • Chest pain



  • Shortness of breath

Serum
Pro-BNP Heart Failure Symptoms:


  • Shortness of breath



  • Extremity swelling

Serum


Troponin I


Troponin I is an enzyme found almost exclusively in heart muscle. In the setting of certain conditions such as a heart attack, levels of troponin I become elevated and can remain so for several days. Typical indications for troponin testing in the emergency setting include chest pain or discomfort, heart palpitations, shortness of breath, fatigue, nausea or vomiting, sweating, dizziness or lightheadedness, and pain radiating to the arm, back, or abdomen.


B-type Natriuretic Peptide


B-type natriuretic peptide is a hormone produced by the heart in response to increased stretch of the heart wall. It is a good marker for both right- and left-sided heart failure.


Respiratory


Arterial and Venous Blood Gases


Arterial blood gas (ABG) and venous blood gas (VBG) tests are used to measure the blood pH and the pressures of oxygen (Pa o 2 ) and carbon dioxide (Pa co 2 ) dissolved in the blood. These tests are performed on patients with a variety of critical illnesses, such as severe sepsis, diabetic ketoacidosis, acute respiratory failure, acute respiratory distress syndrome, cardiac arrest, or shock.


In most cases, a VBG suffices to answer the clinical question and is easier and safer to obtain. See Table 7.3 for a summary of indications for ABG and VBG testing.



Table 7.3

Respiratory Point-of-Care Tests












Test Indications Mode of Collection
ABG/VBG Critical Illnesses:


  • Sepsis



  • Diabetic ketoacidosis



  • Acute respiratory/heart failure



  • Cardiac arrest

Serum:


  • Venous or arterial


ABG , Arterial blood gas; VBG , venous blood gas.


Urinary


See Table 7.4 for a summary of indications for urinary POC testing.



Table 7.4

Urinary Point-of-Care Tests












Test Indications Mode of Collection
Urine dip Urinary Tract Infection Symptoms:


  • Urinary burning



  • Frequency/urgency of urination



  • Blood in urine



  • Diabetes patients



  • Trauma patients

Urine

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Jul 15, 2023 | Posted by in EMERGENCY MEDICINE | Comments Off on Point-of-Care Testing

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