CE UPDATE—POINT OF CARE III Richard F. Louie Zuping Tang, MD David G. Shelby, MT Gerald J. Kost, MD, PhD

Point-of-Care Testing: Millennium Technology for Critical Care This is the third article in a 4-part continuing education series on point-of-care testing. After reading this article, the reader will be able to define POCT, identify its advantages and disadvantages, explain its benefits in critical care settings, understand key features in current point-of-care instruments, identify when a pointof-care test may be inaccurate, and recognize important quality management features of point-of-care instruments.

From Point-of-Care Testing Center for Teaching and Research (POCT•CTR), School of Medicine, University of California, Davis. Address correspondence to: Mr Richard F. Louie, Medical Pathology, 3453 Tupper Hall, School of Medicine, University of California, Davis, Davis, CA 95616. E-mail: [email protected]

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Laboratory test results are often pivotal to critical care decisions.1 Testing provides physicians with valuable knowledge about the criticality of the patient so that appropriate therapeutic interventions can be made quickly. There has been growing interest in decentralized laboratory testing, especially point-of-care testing (POCT) in critical care settings (eg, ICU, OR, ED) where rapid therapeutic turnaround time is needed.2,3 However, some types of POCT are controversial because of concern about the accuracy and performance of instruments when used with critically ill patients (ie, glucose meter testing).4,5 Point-of-Care Testing Defined Point-of-care testing is defined as “testing at or near the site of patient care whenever the medical care is needed.”6 The purpose of POCT is to provide immediate information to physicians about the patient’s condition, so that this information can be integrated into appropriate treatment decisions that improve patient outcomes, that is, reduce patients’ criticality, morbidity, and mortality. Point-of-care testing can be performed in different environments, such as in the hospital, at home, or at other locations.

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Types of Point-of-Care Instruments Point-of-care instruments vary widely and can be categorized as “transportable,” “portable,” or “handheld,” based on the format. Some are capable of testing specific analytes, while others are capable of performing an array of tests (eg, electrolytes and blood gases). Tables 1 and 2 list test parameters and specifications of the latest whole-blood analyzer/biosensor platforms and handheld/portable glucose meters, respectively. Point-of-care instruments differ by their method of testing. For example, whole-blood glucose meters are categorized as “electrochemical biosensor,” “reflectance photometry,” or “absorbance photometry.” These instruments are further differentiated by the type of chemistry used to measure the glucose: either glucose oxidase or glucose dehydrogenase enzymes. Advantages of Point-of-Care Testing Table 3 summarizes some of the advantages of POCT. The first advantage of POCT is the short therapeutic turnaround time of patient sample testing.7,8 The average turnaround time expected by critical care physicians is 5 to 15 minutes.1 Stat tests are frequently requested in critical care units. Depending on the instrument used, the type of test, and the number of tests performed, the analysis time of a whole-blood sample can vary from 15 seconds to 2 minutes 20 seconds (Tables 1 and 2). Delays could yield results that do not reflect the patient’s current condition. One benefit of rapid therapeutic turnaround time is that it allows physicians to begin implementing appropriate treatment early, especially for those patients in critical care units where delays can adversely affect patient outcomes. A second advantage to POCT is potential reduction of preanalytic and postanalytic errors. Traditional methods of laboratory testing involve multiple preparatory steps. With increased process steps, there is an increased possibility of introducing preanalytic

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ABSTRACT Point-of-care testing (POCT) is an important diagnostic tool used in various locations in the hospital, especially in critical care settings such as the intensive care unit (ICU), the operating room (OR), and the emergency department (ED).

Table 1. Characteristics of Whole-Blood Analyzers Sample mL) Volume (m 65 or 95

Analysis Time (seconds) Test Analytes (measured) 90-140 pO2, pCO2, pH, Na+, K+, Ca++, Cl-, Hct, urea nitrogen, glucose, lactate, creatinine

Type Handheld

AVL Scientific, Roswell, GA

Transportable

40-161

60-90

pO2, pCO2, pH, Na+, K+, Ca++, Cl-, Hct, Hb, urea nitrogen, glucose, lactate, creatinine

AVL OPTI

AVL Scientific

Portable

125

200 mg/dL

None

10-600

GD

20-65, [Glu] < 200 mg/dL 20-55, [Glu] > 200 mg/dL

None

† The

Table 3. Advantages and Disadvantages of Point-of-Care Testing Advantages Reduced therapeutic turnaround time of diagnostic testing Rapid data availability Reduced preanalytic and postanalytic testing errors Self-contained and user-friendly instruments Small sample volume for a large test menu Shorter patient length of stay Convenience for clinicians Ability to test many types of samples (ie, capillary, saliva, urine) Disadvantages Concerns about inaccuracy, imprecision, and performance (ie, potential interfering substances) Bedside laboratory tests performed by poorly trained nonlaboratorians Quality management/assurance issues and responsibilities not defined Cost of point-of-care testing compared with traditional laboratory testing Quality of testing is operator-dependent Difficulty in integrating test results with hospital information system (HIS) or laboratory information system (LIS)— lack of connectivity Narrower measuring range for some analytes

Improvement Amendments of 1988 (CLIA ’88). Compliance with the Joint Commission on Accreditation of Healthcare Organizations (JCAHO, Oakbrook Terrace, IL) or College of American Pathologists (CAP, Northfield, IL) regulations is voluntary. All medical institutions must comply with state laws. These laboratory testing regulations help to ensure the high-quality performance of the J U LY 2 0 0 0

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respiratory therapists, and pathologists) know the proper operating procedures and limitations of their point-of-care testing instruments, whether they are testing for glucose, electrolytes, blood gases, cardiac markers, coagulation indices, or other analytes. Hospital staff working with these instruments should be familiar with and responsible for quality management of their instruments, to ensure the reliability of the patient test results. Administrative staff (ie, nurse managers, coordinators of point-of-care testing programs, and managers of quality assurance programs) should keep up-to-date with proficiency testing of operators of point-of-care instruments at their facility as well as be able to train new operators and assess operators’ competence. Quality management deals with measures taken by operators of point-of-care instruments to ensure that instruments are accurate and performing optimally. Compromising the accuracy and precision for expeditious testing is not recommended. Each medical institution should have its own quality assurance committee that is responsible for the competence of operators and for decisions about expected performance standards of the entire testing cycle. Additionally, operators must take necessary measures to comply with regulations. To regulate the performance of laboratory testing (including point-of-care testing), the federal government requires that each medical institution meet the standards established by the Clinical Laboratory

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equation to convert to SI units is: mmol/L = mg/dL 3 0.05551. Handheld device for measurement of glucose and ketones planned. Hematocrit limits apply to neonate samples only.

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Table 4. Preanalytic and Postanalytic Errors Preanalytic errors Mishandling and/or mislabeling of patient specimen Contamination of specimen Degradation of specimen due to delays in specimen processing/testing and/or arrival at central laboratory Postanalytic errors Misreporting patient test results Recording wrong patient test results Lost data Delayed reporting of critical results Table 5. Cost Factors in Point-of-Care Testing

instruments as well the proper practice of diagnostic testing by the operators. Quality control compliance is one of the many quality management monitors used routinely with POCT devices. The Figure illustrates documentation of QC compliance rates of critical-care operators and all other operators of point-ofcare devices at the University of California, Davis, Health System (UCDHS). As part of the quality assurance and performance-improvement program at UCDHS, an e-mail progress report is issued monthly to nurse supervisors of each department by the pathology POCT manager. The report provides an assessment of the overall QC compliance rate of that department and compares the department’s performance to the rest of the hospital. If the department compliance rate falls below the rest of the hospital, a message in the e-mail emphasizes the necessity for improvement to meet JCAHO and CLIA guidelines. Performance has improved steadily with the electronic broadcast approach. Finally, there is growing debate about the cost-effectiveness of POCT. It has been argued that the cost for POCT compared to centralized laboratory testing may be less, more, or may show no difference.19,20,21 Table 5 lists some factors that contribute to the costs of POCT. While it appears that POCT may be more expensive than laboratory testing, some argue that the benefits of POCT—the small sample volume12 and short therapeutic turnaround time7—could shorten the length of patient stay or offset the costs of POCT—or both. POCT in the operating room is cost-effective for hemostasis evaluation and transfusion management.22 In some cases, such as rapid 406

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Technology of Whole-Blood Biosensors Whole-blood analyzers currently use both electrochemical sensors and other methods (ie, optical sensors) for specimen analysis. Electrochemical sensors are categorized as either potentiometric or amperometric and include the ion-selective electrode (ISE) and substrate-specific electrode (SSE). The electrical conductance (impedance) sensor (ECS) is used to measure hematocrit indirectly. Optical sensor technology includes spectrophotometry, absorbance photometry, and reflectance photometry. Table 6 lists analytes commonly tested with these methods. Ion-selective electrodes operate by determining the electrical potential (relative to the reference electrode potential) established by ions across selectively permeable membranes. The difference in potential across the membrane is logarithmically proportional to the specific ion concentration (activity) in the blood. The operation of a substrate-specific electrode is illustrated when testing for glucose using the YSI 2300 Stat Glucose/Lactate Analyzer. Glucose is oxidized with the catalysis of glucose oxidase to form gluconic acid and hydrogen peroxide. Hydrogen peroxide subsequently becomes oxidized, and a platinum electrode measures the current that forms. The current formed is proportional to the glucose (substrate) concentration (molality). The electrical conductance sensor operates by measuring the impedance of the current flow in the sample. The impedance of the current is measured by applying an alternating voltage across 2 or more electrodes in contact with the blood sample. Features of Current Whole-Blood Point-of-Care Analyzers and Glucose Meters Notable features of point-of-care instruments include expanded test options, shortened analysis time, reduced sample test volume, and automated quality management. Current instruments are able to measure up to 14 different tests per sample of blood, compared to the 8 to 11 tests in previous generations. Many of the current instruments require a small blood volume to perform a test—as little as 2.5 µL for a single measurement on a handheld glucose meter, or as little as 40 µL for 1 or 2 measurements, such as glucose and lactate, on a whole-blood analyzer. The analysis time can be as rapid as 15 seconds for a single measurement, or 45 seconds for a multipleparameter test; hence, shortening the therapeutic turnaround time. The latest whole-blood analyzers have the capability of providing selective testing; that is, the operator may select the tests to be performed, thereby eliminating unnecessary tests, which can generate financial losses and waste patient blood.

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Supplies (eg, reagents, disposable cartridges, test strips) and equipment Training and retraining of instrument operators Maintenance of instruments, including replacing defective instruments Additional labor on the part of nonlaboratorians (eg, nurses) to run patient tests New software that enables patient results to be entered into hospital/laboratory information systems (HIS/LIS) Troubleshooting instruments Consultation services for instrumentation problems Performing comparison studies of new instruments and methodologies with existing instruments Accreditation and proficiency testing fees Duplication, repeated tests, verification, and validation

parathyroid hormone (PTH) testing for parathyroid surgery, speed alone is crucial in saving operating room time and reducing the length of hospitalization.23 Recent studies demonstrated that point-of-care testing can reduce the length of hospital stay24 and time in the emergency department,25 but further study is needed to validate these results.

100 90

Compliance Rate (%)

80 70 60 50 40 30

All critical care units All hospital areas

20 10

Sep 99

Jul 99

Aug 99

Jun 99

Apr 99

May 99

Feb 99

Mar 99

Jan 99

Dec 98

Oct 98

Nov 98

Sep 98

Jul 98

Aug 98

Jun 98

Apr 98

May 98

Feb 98

Mar 98

Jan 98

Dec 97

0

Month/Year Quality control (QC) compliance rates. QC compliance rates are shown as a function of time for critical care settings and all hospital areas at the University of California, Davis, Health System from January 1998 through September 1999. The line for all critical care units is based on 14 different critical care settings, including intensive care units, the operating room, and the emergency department. The line for all hospital areas is based on 57 settings. The graph shows progressive performance enhancement after instituting electronic mail broadcasting.

thus ensuring proper usage of the instrument. Some instruments require that proper patient identification be entered before testing can proceed. This action ensures proper documentation of test results.

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Future of Point-of-Care Instruments and Testing An important issue to address now about POCT is the accuracy, performance, and reliability of these

Table 6. Methods for Analyte Measurements Substrate-Specific Electrode (SSE) No

Mg++

Yes

No

K+

Yes

No

No

No

Cl–

Yes

No

No

No

No

Analyte-Specific Optical Sensor (ASOS) No No

Na++

Yes

No

No

No

pH PCO2

Yes CO2-sensitive buffer, with pH electrode

No No

No No

Yes Yes

pO2

No

Amperometric

No

Yes

Glucose

No

Yes

No

No

Lactate

No

Yes

No

No

Urea Nitrogen

No

Yes

No

No

Creatinine

No

Yes

No

No

Hematocrit

No

No

Yes

No

Hemoglobin

No

No

No

Multiwavelength reflectance

Acid displacement, CO2-sensitive buffer, with pH electrode

No

No

No

No

No

Optical reflectance

Total CO2

O2 saturation

No

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Analyte Ca++

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Method Electrical Conductance Sensor (ECS) No

Ion-Selective Electrode (ISE) Yes

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Advanced quality management features also appear on the latest instruments. Most wholeblood analyzers are equipped with automatic internal 1- and 2-point calibrations at various time intervals ranging from every 15 minutes to every 2 hours. Some instruments have automatic or electronic QC (EQC). Automatic QC ensures that QC testing is performed routinely at regular intervals. The purpose of EQC is to test the electronics; that is, the internal and analyte circuits of the instrument. However, EQC doesn’t validate the performance of the test cartridges or of the operator. EQC can help generate cost savings because it is convenient, can be completed quickly, is reagentless, requires only a reusable EQC card, and is a beneficial feature that assesses the electronic measurement cycle of the instrument. It is important to realize that manufacturers of instruments with the EQC feature do not recommend substituting EQC for aqueous QC. Aqueous and electronic QC should both be performed. A QC “lockout” feature, when enabled, does not allow the operator to perform any patient testing unless quality control testing has been performed and has satisfied the vendor-specified QC ranges. Other lockout and security features include a password option, which must be entered by a certified operator before the instrument can be used for patient testing,

Look for the CE Update exam on Point-of-Care (004) in the August issue of Laboratory Medicine. Participants will earn 4 CMLE credit hours.

Acknowledgments The authors would like to acknowledge Joan Bullock for her contribution of information and insights into the Quality Assurance Program at the University of California, Davis, Health System, and thank the vendors for providing information on their products.

References 1. Harvey MA. Point-of-care laboratory testing in critical care. Am J Crit Care. 1999;8:72-83. 2. Lamb LS, Parrish RS, Goran SF, et al. Current nursing practice of point-of-care laboratory diagnostic testing in critical care units. Am J Crit Care. 1995;4:429-434. 3. Kost GJ, Ehrmeyer SS, Chernow B, et al. The laboratory-clinical interface: point-of-care testing. Chest. 1999;115:1140-1154. 4. Kost GJ, Vu H, Lee JH, et al. Multicenter study of oxygeninsensitive handheld glucose point-of-care testing in critical care/hospital/ambulatory patients in the United States and Canada. Crit Care Med. 1998; 26:581-590.

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5. Louie RF, Tang Z, Sutton DV, et al. Point-of-care testing: effects of critical care variables, influence of reference instruments, and a modular glucose meter design. Arch Pathol Lab Med. 2000;124:257-266. 6. Kost GJ. Guidelines for point-of-care testing: improving patient outcomes. Am J Clin Pathol. 1995;104(suppl 1):S111S127. 7. Kilgore ML, Steindel SJ, Smith JA. Evaluating stat testing options in an academic health center: turnaround time and staff satisfaction. Clin Chem. 1998;44:1597-1603. 8. Chernow B, Salem M, Sacey J. Blood conservation: a critical care imperative. Crit Care Med. 1991;19:313-314. 9. Zimmerman JE, Seveff MG, Sun X, et al. Evaluating laboratory usage in the intensive care unit: patient and institutional characteristics that influence frequency of blood sampling. Crit Care Med. 1997;25:737-748. 10. Peruzzi WT, Parker MA, Lichtenthal PR, et al. A clinical evaluation of a blood conservation device in medical intensive care unit patients. Crit Care Med. 1993;21:501-506. 11. Chernow B. Blood conservation in critical care: the evidence accumulates. Crit Care Med. 1993;21:481-482. 12. Salem M, Chernow B, Burke, et al. Bedside diagnostic testing: its accuracy, rapidity, and utility in blood conservation. JAMA. 1991;266:382-389. 13. Wahr JA, Lau W, Tremper KK, et al. Accuracy and precision of a new, portable, handheld blood gas analyzer, the IRMA. J Clin Monit. 1996;12:317-324. 14. Zaloga GP, Roberts PR, Black K, et al. Hand-held blood gas analyzer is accurate in the critical care setting. Crit Care Med. 1996;24:957-962. 15. Tang Z, Lee JH, Louie RF, et al. Effects of different hematocrits on glucose measurements with handheld meters for point-of-care testing. Arch Pathol Lab Med. In press. 16. Tang Z, Du X, Louie RF, et al. Effects of pH on glucose measurements with handheld glucose meters and portable glucose analyzer for point-of-care testing. Arch Pathol Lab Med. 2000;124:577-582. 17. Lamb LS. Responsibilities in point-of-care testing: an institutional perspective. Arch Pathol Lab Med. 1995;119:886-889. 18. Zaloga GP, Dudas L, Roberts P, et al. Near-patient blood gas and electrolyte analyses are accurate when performed by non-laboratory-trained individuals. J Clin Monit. 1993;9:341-346. 19. Kilgore ML, Steindel SJ, Smith JA. Cost analysis for decision support: the case of comparing centralized versus distributed methods for blood gas testing. Journal of Healthcare Management. 1999;44:207-215. 20. Halpern MT, Palmer CS, Simpson KN, et al. The economic and clinical efficiency of point-of-care testing for critically ill patients: a decision-analysis model. Am J Medical Qual. 1998;13:3-12. 21. De Cresce RP, Phillips DL, Howanitz PJ. Financial justification of alternate site testing. Arch Pathol Lab Med. 1995;119:898-901. 22. Depotis GJ, Santoro SA, Spitznagel E, et al. Prospective evaluation and clinical utility of on-site monitoring of coagulation in patients undergoing cardiac operation. J Thorac Cardiovasc Surg. 1994;107:271-279. 23. Scott MG. Is faster better? An outcomes approach to POCT implementation decisions. In: Managing Your POCT Program for Success. Washington, DC: American Association for Clinical Chemistry. Audio Conference, January 20, 2000. 24. Collinson PO. The need for a point of care testing: an evidence-based appraisal. Scand J Clin Lab Invest. 1999;59(suppl 230):67-73. 25. Murray RP, Leroux M, Sabga E, et al. Effects of point of care testing on length of stay in an adult emergency department. J Emerg Med. 1999;17:811-814. 26. Kost GJ. Point-of-care testing. In: Meyer RA, ed. Encyclopedia of Analytical Chemistry: Instruments and Applications. New York, NY: John Wiley and Sons; 2000, chap 540. In press.

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instruments for patient testing in the critical care setting. More study is needed to examine the limitations of these instruments and to resolve any potential error sources (eg, interfering substances) that may affect instrument performance. However, in regard to short-term advances with pointof-care technology, we will see continued expansion of test menus, shorter analysis time, and reduced sample volume. For example, several devices are now available for hemostasis testing at the point of care,26 for other point-of-care analytes not listed in Table 1 (eg, ß-hydroxybutyrate, therapeutic drugs, and drugs of abuse), and for cardiac-injury markers (eg, troponin I, CK-MB, and myoglobin). Several additional point-of-care analytes are under development. Additionally, POCT will be “connected” in the near future. Test results will be downloaded and recorded readily into the hospital and laboratory information system (HIS/LIS). The first meeting of the Connectivity Industry Consortium (CIC) on POCT was held October 20, 1999, in Redwood City, CA, to facilitate this process. The CIC members set a goal of writing and publishing connectivity standards for near-patient and point-of-care instruments by the end of the year 2000. Point-of-care testing undoubtedly will take a more active role in critical care settings. It will be used more for on-site diagnostic testing and trend monitoring of patient conditions, due in part to the increasing percentage of critically ill patients in hospitals, the need for shorter therapeutic turnaround time, and bidirectional connectivity of transportable, portable, and handheld devices. While POCT may not necessarily replace centralized laboratory testing, it is becoming an important modality for improving patient care and outcomes.l