Laboratory Tests in the Intensive Care Unit
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LABORATORY TESTS IN THE INTENSIVE CARE UNIT JASSIN M. JOURIA, MD DR. JASSIN M. JOURIA IS A MEDICAL DOCTOR, PROFESSOR OF ACADEMIC MEDICINE, AND MEDICAL AUTHOR. HE GRADUATED FROM ROSS UNIVERSITY SCHOOL OF MEDICINE AND HAS COMPLETED HIS CLINICAL CLERKSHIP TRAINING IN VARIOUS TEACHING HOSPITALS THROUGHOUT NEW YORK, INCLUDING KING’S COUNTY HOSPITAL CENTER AND BROOKDALE MEDICAL CENTER, AMONG OTHERS. DR. JOURIA HAS PASSED ALL USMLE MEDICAL BOARD EXAMS, AND HAS SERVED AS A TEST PREP TUTOR AND INSTRUCTOR FOR KAPLAN. HE HAS DEVELOPED SEVERAL MEDICAL COURSES AND CURRICULA FOR A VARIETY OF EDUCATIONAL INSTITUTIONS. DR. JOURIA HAS ALSO SERVED ON MULTIPLE LEVELS IN THE ACADEMIC FIELD INCLUDING FACULTY MEMBER AND DEPARTMENT CHAIR. DR. JOURIA CONTINUES TO SERVES AS A SUBJECT MATTER EXPERT FOR SEVERAL CONTINUING EDUCATION ORGANIZATIONS COVERING MULTIPLE BASIC MEDICAL SCIENCES. HE HAS ALSO DEVELOPED SEVERAL CONTINUING MEDICAL EDUCATION COURSES COVERING VARIOUS TOPICS IN CLINICAL MEDICINE. RECENTLY, DR. JOURIA HAS BEEN CONTRACTED BY THE UNIVERSITY OF MIAMI/JACKSON MEMORIAL HOSPITAL’S DEPARTMENT OF SURGERY TO DEVELOP AN E-MODULE TRAINING SERIES FOR TRAUMA PATIENT MANAGEMENT. DR. JOURIA IS CURRENTLY AUTHORING AN ACADEMIC TEXTBOOK ON HUMAN ANATOMY & PHYSIOLOGY. Abstract When patients are brought to the intensive care unit, extensive laboratory testing is often considered necessary in order to diagnose and treat critical conditions. However, laboratory tests are not without risk. Results can be misleading, and the testing itself can be harmful, such as potentially causing iatrogenic anemia. Medical professionals need to take a sensible approach to laboratory testing for patients in the intensive care unit, focusing on the benefits and risks of each test and being mindful of the probability of disease. 1 nursece4less.com nursece4less.com nursece4less.com nursece4less.com Policy Statement This activity has been planned and implemented in accordance with the policies of NurseCe4Less.com and the continuing nursing education requirements of the American Nurses Credentialing Center's Commission on Accreditation for registered nurses. It is the policy of NurseCe4Less.com to ensure objectivity, transparency, and best practice in clinical education for all continuing nursing education (CNE) activities. Continuing Education Credit Designation This educational activity is credited for 2.5 hours. Nurses may only claim credit commensurate with the credit awarded for completion of this course activity. Statement of Learning Need Clinicians caring for patients in the Intensive Care Unit are required to interpret laboratory tests and be able to manage safe and appropriate laboratory testing guidelines. Health professionals working with critically ill patients need to take an evidenced-based and rational approach to laboratory testing, including an understanding of the benefits and risks of each test relative to a disease process. 2 nursece4less.com nursece4less.com nursece4less.com nursece4less.com Course Purpose To provide health clinicians with knowledge of different types of laboratory testing for patients in the ICU as well as the benefits and risks of varied tests. Target Audience Advanced Practice Registered Nurses and Registered Nurses (Interdisciplinary Health Team Members, including Vocational Nurses and Medical Assistants may obtain a Certificate of Completion) Course Author & Planning Team Conflict of Interest Disclosures Jassin M. Jouria, MD, William S. Cook, PhD, Douglas Lawrence, MA, Susan DePasquale, MSN, FPMHNP-BC – all have no disclosures Acknowledgement of Commercial Support There is no commercial support for this course. Please take time to complete a self-assessment of knowledge, on page 4, sample questions before reading the article. Opportunity to complete a self-assessment of knowledge learned will be provided at the end of the course. 3 nursece4less.com nursece4less.com nursece4less.com nursece4less.com 1. Laboratory test sensitivity refers to the ability of a a. patient to tolerate a test. b. test to identify the presence of a disease or condition correctly. c. test to identify true negative. d. test to identify the absence of a disease or condition correctly. 2. Transfusion of whole blood, packed cells or blood components has been a. shown to offer a survival advantage to patients. b. known to reduce production of erythropoietin. c. shown to depress new blood cells. d. associated with the risk of infection. 3. True or False: Wellness testing is not an aspect of lab testing in the ICU setting. a. True b. False 4. Red blood cell transfusion is indicated for a patient a. with adequate blood flow (hemodynamic stability). b. with acute hemorrhage but only in single units. c. with evidence of hemorrhagic shock. d. as an absolute method to improve tissue oxygen consumption. 5. The Nyquist-Shannon Theorem posits that there is an appropriate relationship between the number of samplings and the likelihood that a. a test will identify the presence of a disease. b. the risk of clinically inappropriate treatments c. there will be a medically appropriate solution. d. the sample signal will be properly determined. 4 nursece4less.com nursece4less.com nursece4less.com nursece4less.com Introduction There are surprisingly relatively few studies that address the question of what tests are the most effective and offer the most benefit for patients in the Intensive Care Unit. Evidence and data should drive medical decisions as much as possible, particularly with critically ill patients. The Intensive Care Unit is an environment where increased patient monitoring, data acquisition and frequent testing are very common. At first glance, one might reasonably believe that the more data and information one could acquire, the better patient interests can be served. However, frequent blood draws carry their own perils. These include anemia, increased need for transfusions of whole blood or blood components and infection. This course focuses on the common laboratory tests requested by clinicians caring for critically ill patients. Overview Of Laboratory Testing For Critically Ill Patients Studies focused on laboratory testing in the Intensive Care Unit (ICU) have revealed that ICU patients had from 40 to 70 mL of blood drawn daily, amounting to over 1 L of blood during their ICU stay;1 and, also that conservative blood sampling strategies are not widely used. In a recent review, the total blood volume removed from ICU patients was 299 ± 355 mL over 48 hours. Utilizing small-volume phlebotomy tube (SVPT) versus conventional-volume phlebotomy tube (CVPT) decreased this volume to 174 ± 182 mL.2 Another aspect related to the drawback of frequent blood draws involved patient discomfort in the ICU setting at a time when they can 5 nursece4less.com nursece4less.com nursece4less.com nursece4less.com often least endure more discomfort. Frequent blood draws can disrupt needed sleep and cause additional stress to patients. There is also an increased risk of false positive or false negative laboratory test results that can increase the risk of clinically inappropriate treatments. Test sensitivity is the ability of any test to correctly identify the presence of a disease or condition (true positives) while specificity is the ability of any test to correctly identify the absence of a disease or condition (true negatives). Clinicians should only order those tests that have a reasonable probability of providing useful information, either for ruling in or for ruling out a particular diagnosis. Ruling out a diagnosis with laboratory testing has the highest power for diagnoses with a low probability. Wellness Testing Wellness testing is obviously not an aspect of lab testing in the ICU setting. Lipid panels or blood glucose screening tests have a definite place in populations at risk for hyperlipidemia or diabetes. Genetic screening may make sense for newborns, but it has little application for patients in the ICU. The general recommendation in the ICU is to order tests for which, if the results indicate a problem, there is a medically appropriate solution. Nyquist-Shannon Theorem The Nyquist-Shannon Theorem posits that there is an appropriate relationship between the number of samplings and the likelihood that the sample values will be properly determined; in other words, there is 6 nursece4less.com nursece4less.com nursece4less.com nursece4less.com a relationship between how often one should sample a varying laboratory test.3 For example, blood glucose values will vary based on meal frequency or if the patient is receiving total parenteral nutrition. Oversampling (for example) every 30 minutes will not reveal any more information as compared to sampling 2 hours after a meal. With oversampling, while sensitivity may be increased, specificity will necessarily be decreased, which will reduce the accuracy of the test. Undersampling, on the other hand, can be just as problematic. Reflexive testing algorithms as well as reflective testing have significant clinical utility. Using an algorithmic approach, clinicians are able to order sequential laboratory tests or a laboratory specialist will get straight to the point of a diagnostic concern through further testing. There are a number of tools in the laboratory toolbox that can be effectively utilized in the ICU setting.4 These include the following strong tools adapted for the ICU setting. Laboratory Utilization Toolbox TOOL TARGET STRENGTHS WEAKNESSES Laboratory Test All tests, but Provides a Requires a buy-in Formulary particularly