Contemporary Practice in Clinical Chemistry

William Clarke,Mark Marzinke

• Éditeur: Academic Press
• Année: 2020
• ISBN:
  9780128158333
• Édition: 4
• Sujet: Sciences biologiques
• Sous-sujet: Biochimie

Contemporary Practice in Clinical Chemistry, Fourth Edition, provides a clear and concise overview of important topics in the field. This new edition is useful for students, residents and fellows in clinical chemistry and pathology, presenting an introduction and overview of the field to assist readers as they in review and prepare for board certification examinations. For new medical technologists, the book provides context for understanding the clinical utility of tests that they perform or use in other areas in the clinical laboratory. For experienced laboratorians, this revision continues to provide an opportunity for exposure to more recent trends and developments in clinical chemistry.

• Includes enhanced illustration and new and revised color figures
• Provides improved self-assessment questions and end-of-chapter assessment questions

Chapter 1

Preanalytical variation

Zahra Shajani-Yi and James H. Nichols, Department of Pathology, Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, TN, United States

Abstract

Laboratory errors can occur in the preanalytical phase and include issues with sample collection (hemolysis, incorrect tube type, or order of draw), interfering substances (lipemia, bilirubin, and biotin), and sample processing, storage, and transport. An understanding of the causes of preanalytical errors and ongoing, proactive monitoring allows the laboratory to develop preventive measures to mitigate the risk of releasing inaccurate results. This chapter focuses on the common sources of preanalytical variation and discusses the quality processes for reducing the potential for preanalytical errors.

Keywords

Sample collection; tube type or tube additives; specimen collection and processing; hemolysis; lipemia; icterus; preanalytic variation or errors

Learning objectives

After reviewing this chapter, the reader will be able to:

• • Understand why preanalytical variation is a significant contributor to laboratory errors.
• • Identify the common sources of preanalytical variation.
• • Discuss the potential effects of phlebotomy, tube additives, and order of draw.
• • Discuss ways to detect and reduce preanalytical errors.

Laboratory testing comprises the majority of information in the electronic medical record [1,2]. Laboratory services accounted for 2.3% of health care expenditures in the United States with over 6.8 billion laboratory tests performed, with clinical pathology, anatomic pathology/cytology, and molecular/esoteric tests accounting for 66%, 23%, and 8% of performed tests respectively [3]. Hospital test volumes also grew by an average of 6% annually [3]. As the number of laboratory tests increases, the opportunity for errors that adversely affect patient care also increases. These errors can occur in any of the three phases of the total testing process: the preanalytic, analytic, or postanalytic phase (Fig. 1.1). An understanding of the sequence of events required for laboratory testing provides a foundation for assessing the likelihood of errors occurring at each step of the testing process.

Figure 1.1 Steps in the testing process.

This process begins as the clinician examines a patient and determines the need for a laboratory test. The correct test must be ordered, the patient must be prepared, and an appropriate sample must be collected. The sample is then transported to a laboratory, received, and processed for analysis. During analysis, the sample may be aliquoted, diluted, or subjected to subsequent testing before the final result can be verified for release. The clinician must then receive and interpret the result and decide on the appropriate treatment or follow-up and place the follow-up orders and instructions, and staff must schedule and carry out these orders for the patient.

Historically, quality initiatives have focused on the analytical phase of testing, and over the years, the number of errors attributed to this phase has decreased [4]. Interestingly, the majority of laboratory-related errors occur outside of the actual laboratory, either in the preanalytical or postanalytical phase. Recent studies report that approximately 46%–68% of all laboratory errors occur in the preanalytical phase [5,6].

Errors can occur during: (a) the ordering process, either through the clinician laboratory test order entry or when the order is manually transcribed; and (b) sample collection if a patient is not properly prepared or the sample is incorrectly labeled. Additional errors include: (c) specimen collection where specimens are either collected in the wrong type of tube with potentially interfering additives or if the tubes are collected in the wrong order; and (d) delays and/or inappropriate storage or handling during delivery of specimens to the laboratory. Finally, upon reaching the laboratory, testing accuracy is compromised if (e) samples are not adequately processed and stored for analysis.

Accurate laboratory test results demand high-quality specimens. Unfortunately, in most systems, the resources allocated for the pre- and postanalytical processes are not sufficient, as the importance of preanalytics is often overlooked. Many of the mistakes that are referred to as “laboratory errors” arise due to poor communication and action by others involved in the testing process or poorly designed processes that are outside of the laboratory’s control. This chapter will focus on the most common sources of preanalytical variation and discuss some quality system processes for reducing the preanalytical errors. Understanding the causes of preanalytical errors coupled with proactive ongoing monitoring allows the laboratory to develop preventive measures to mitigate the risk of releasing inaccurate results.

Order entry

Errors in laboratory orders commonly occur due to the similarity of test names, improper use of synonyms, failure to enter orders correctly into the hospital electronic computer system, lack of knowledge about tests, and transcription errors (Table 1.1). Tests that are commonly misordered due to similar names are: (1) C-reactive protein for inflammation versus high-sensitivity C-reactive protein for cardiovascular risk assessment; (2) lipoprotein versus lipoprotein panel; (3) calculated versus direct low-density lipoprotein; and (4) 1,25-vitamin D (calcitriol) versus 25-vitamin D (calcidiol). Tests that also require supplementary clinical information often have high rates of errors. At our institution, in order to calculate a second trimester prenatal quad screen report, information such as the patient’s date of birth, estimated due date, ethnicity, weight, diabetics, and smoking status must be provided by the clinician. Inaccurate reporting of such clinical data can lead to improper risk factors being calculated and subsequently reported.

Table 1.1

Sources of preanalytical variation.

Source of variation	Potential solution
Order entry
Similar test names Duplicate orders Transcription entry errors	Set up computer order entry screens with explanatory notes or pop-up screens Construct expert systems and rules to detect duplicate orders Verify computer entry against written orders
Patient preparation
Diet/supplements Time of collection	Fast or restrict diet if necessary before testing Ask patients about supplements (e.g., biotin) Proper collection for TDM and hormones Document drug administration accurately with respect to specimen collection
Specimen collection
Patient identification Needle size Tube selection/order of draw Prolonged use of tourniquet Fist clenching during phlebotomy Inadequate tube filling Specimen clotting Urine stability	Verify the use of two identifiers Prevent hemolysis by routine smaller gauge needles Sign posted and smart laboratory labels Limit tourniquet use to 1 min Encourage patients to rest arm during phlebotomy Use vacuum collection tubes Ensure tubes are more than 3/4 full during collection Mix tubes by gentle inversion immediately Provide preservatives in collection container
Processing, transportation, and storage
Outpatient clinic delayed processing Exposure of tubes to environment Add-on testing	Provide equipment to process specimens on site Protect and insulate specimens during transportation Validate and optimize storage stability for each analyte

Differences in methodology can also have implications for clinicians when they are trying to order a test. For example, testosterone can be measured accurately for most men by immunoassay, whereas women, children, and men with hypogonadism have lower testosterone concentrations and should therefore have testosterone measured by mass spectrometry. Ideally, a test name and description should be able to convey to the ordering provider if the test is appropriate for their patient. Further adding to these issues are the cases where orders are manually transcribed from written notes or requisitions, such as outpatient locations. These transcriptions are often performed in the specimen receiving section, where staff try to decode and/o...