Models for point-of-care testing of critical care analytes

Introduction

Point-of-care testing (POCT) is now common in many near-patient and critical care settings. For blood gas and electrolyte testing, this includes operating rooms (ORs), intensive care units (ICUs), cardiac catheterization labs (CCL), emergency departments (ED), and many primary care clinic settings. POCT has several distinct benefits, such as minimizing or eliminating specimen transportation and processing which have the added benefits of minimizing preanalytical effects and providing faster turnaround times (TAT). Some systems offer a variety of test cartridges that provide a flexible test menu. More rapid test results potentially allow more prompt medical decisions, which can lead to improved patient outcomes, operational efficiencies, and patient satisfaction. For a variety of reasons, POCT devices usually require less blood volume especially compared to central laboratory requirements and can be especially attractive in pediatric areas ( ) . As POCT is not usually performed by trained laboratory personnel, maintaining regulatory compliance and quality assurance with POCT are challenges that require continual surveillance.

Most current POCT devices can be interfaced to both laboratory information systems (LIS) and electronic medical record systems (EMR). For today's current high test volumes and the need to minimize transcription errors, connection to information systems is essential. Well-functioning information systems can automatically transfer (download) results from the analyzer and display them to the physician. This ensures both accuracy and rapid delivery of results to multiple caregivers.

An issue that sometimes arises is the potential for POCT to replace central laboratory (CL) testing. POCT has, and will, replace some CL testing, with POCT accounting for 10%–20% of clinical laboratory testing, depending on the location. This is true where rapid results are essential for urgent decisions, and helpful in nonurgent settings such as clinics that potentially allow the physician to evaluate the results and discuss with the patient while still present. In addition, POCT can replace near-patient laboratories that are extremely inefficient. However, the sheer test volume handled by most central laboratories cannot be replaced by POCT, at least with present technology. Most, if not all, POCT devices are not equipped to handle large test volumes and generally would be far more expensive to operate.

Importance of POCT in answering clinical needs

In emergency and critical care settings, such as ICUs, ORs, EDs, and CCLs, blood gas and electrolytes can change rapidly and often require equally rapid clinical decisions. In these settings, a variety of patients may be seen, including burn, trauma, chest pain, sepsis, and stroke patients, and those on ventilators ( ) . Because these situations usually require continuous monitoring, POCT is well suited to provide rapid results that aid in urgent clinical decisions that may lead to improved patient outcomes ( ) . A recent document notes that when the laboratory TAT exceeds 25% of the desired decision time, POCT should be considered ( ) .

Blood gases . Because pH, p CO ₂ , and p O ₂ can change suddenly with potentially life-threatening consequences, blood gas results are virtually always required immediately. Blood gas results by POCT can be most helpful in ICUs and EDs for patients under anesthesia or on ventilation, or those with cardiac failure, hypoxemia, acidosis, sepsis, or any shock state ( ) .

Sodium, potassium, chloride . Detecting, monitoring, and treating abnormal electrolyte concentrations are critically important in many patients. As noted in a review ( ) , many studies conclude that rapid results provided by POCT reduce therapeutic intervention time compared to TAT for results from central laboratories.

Ionized calcium . In ICU settings, prompt ionized calcium results are especially helpful for patients with sepsis, hypocalcemia, arrhythmias related to hyperkalemia, hypotension, heart failure, shock, and burns ( ) . Ionized calcium concentrations below 0.70 mmol/L have been associated with higher morbidity and mortality ( ) .

Lactate . Many studies have shown that elevated blood lactate concentrations are associated with increased mortality and that rapid results by POCT can be beneficial ( , ) . Critical concentrations of lactate differ, with some finding that concentrations >4.0 mmol/L were associated with a much higher risk of mortality in sepsis ( ) , and others finding that lactates >2.0 mmol/L on admission to the ICU was associated with higher mortality ( ) .

Types of POCT analyzers

Stationary “hybrid” analyzers used in POCT areas . Hybrid analyzers are those with qualities that are suitable for use in both clinical laboratories and in certain POCT locations. Typically, maintenance involves simply replacing one or only a few test packs that contain reagents, controls, calibrants, sampling and flow systems, and sometimes electrodes and optical detection systems in packs that are relatively easily replaced. Current hybrid analyzers typically give results in 1 min or less and sample volume requirements are similar to and sometimes less than for portable analyzers. They have both ion-selective-electrode (ISE) and optical detection systems to measure the full panel of “blood gas” tests, including electrolytes, glucose, lactate, and hemoglobin with variants. Because these analyzers cost more and are typically more expensive to operate for lower test volumes, they are more suited for areas with relatively higher test volumes.

Portable analyzers used for POCT . Portable analyzers are handheld and are easily transported or carried for POC testing. They may be either located in a docking station for use when such testing is needed or carried continually by those who do more frequent blood gas testing, such as respiratory therapists. These instruments have the distinct advantages of portability, small sample volume requirement, flexible test menu (although sometimes requiring multiple test cartridges), and usually lower cost per instrument. For small test volumes, they can be less costly per test than hybrid systems, but the cost per reportable result is usually higher for large test volumes. Because most use single-use test cartridges, the overall time to obtain the final result is typically longer than with a hybrid analyzer, so portable devices are not well-suited for handling large test volumes. Analytical quality is quite good, but usually a notch below the standards of a bench or hybrid analyzer. Most or all of the handheld portable systems are not able to directly measure the cooximetry tests (Hb, O ₂ Hb, CO-Hb, and met-Hb). Instead, hematocrit is measured by impedance that is used to calculate Hb, For some complete test panels, two cartridges may be needed.

Selecting an analyzer for POCT

Many factors are involved in selecting a POC analyzer that fulfills the clinical and operational needs. These include the following ( ) :

• Analyzer quality

• Staffing needs

• Time to the result and time to recycle to the next sample

• Material and storage requirements

• Flexibility of information systems to meet testing and monitoring needs

• Cost justification

• Complexity and ease of use of the test system by nonlaboratory personnel.

• Ease of testing QC material

• Size of the analyzer

Analyzer quality for POCT

The reliability and performance characteristics of a POC analyzer must suit the clinical needs of the physician in monitoring and treating the patient. While POC devices provide quality results, they often use very different technology than core lab instruments and generally have some analytical differences (biases, imprecision, interferences) relative to lab instruments.

Quality begins with the manufacturer of the devices and must meet standards of safety, analytical quality, reliability, and relative ease of use among different testing personnel. Operator performance is also highly important so that a good device used with poor technique will likely give an unreliable result. The CDC studied the use of glucometers in various settings and found the following ( ) :

• Best performance was POCT done by medical technologists associated with hospital labs

• Worst POCT performance was by nonlab personnel in physician offices;

• Intermediate performance was from nonlab personnel trained by laboratory or laboratory-trained users.

To summarize, the laboratory should be responsible for oversight of POCT to ensure quality and to educate users to understand that quality includes the following:

• Appropriate planning

• Implementing and selecting appropriate POCT systems that fulfill the clinical needs

• Ensuring consistent analysis of quality control material and timely evaluation of analyzer functions

• Timely and successful results on external quality assessment by proficiency testing

• Training and continual education of POCT operators

• Rapid and easily documented clinical results

• Selecting analyzers that have the same or similar reference intervals (ranges) as those for the laboratory

Information connectivity and data management

Information technology related to POCT is the science of how information and data are acquired, processed and organized, stored, and transmitted or communicated for both immediate and retrospective clinical interpretation. Data management systems automate the ordering and billing of results, monitor QC data for trends or shifts, report patient results, detect and notify laboratory staff of error codes, and document competency training of operators ( ) .

Indeed, functional interfacing of POCT devices to LIS and the EMR are essential in hospital settings. In evaluating a POC analyzer, the laboratory staff must determine and understand the ability of the instrument system to interface with the existing LIS and EMR, or what middleware system must be purchased for such compatibility. Automatic transfer of results virtually eliminates transcription errors, which would be an overwhelming problem in a POC setting with end users entering results. With either portable or stationary “hybrid” analyzers, wireless connection is highly desirable, or at least a docking station that will automatically download any results stored in the analyzer. If wireless connectivity is not available, stationary analyzers will require “hard-wiring” to information systems.

Another developing area is transmitting results directly to the patient as a consumer. This is called direct-to-consumer (DTC) laboratory testing that permits consumers to order laboratory tests directly from a laboratory without necessarily having to work with a healthcare provider. Test results given to the consumer may be used to monitor an existing health condition, identify a previously unknown medical disorder, or provide personal health data. While DTC laboratory testing aims to increase individuals' engagement in managing their healthcare, the critical nature of blood gases, the specimen collection and handling requirements, and the moderate complexity of blood gas and electrolyte testing are not conducive to DTC testing. There are many issues with DTC testing that are discussed in a position statement ( ) .