Clinical Biochemistry

Peter Rae, Mike Crane, Rebecca Pattenden

• Publisher: Wiley-Blackwell
• Year: 2017
• Print ISBN: 9781119248682
• eBook ISBN: 9781119248637
• Edition: 10
• Topic: Medicine
• Subtopic: Biochemistry in Medicine

Clinical Biochemistry Lecture Notes presents the fundamental science behind common biochemical investigations used in clinical practice. Taking a system-based approach, it explores the underlying physiological rationale for tests, with each test explained within the context of disruption by disease. It also explores the value and limitations of biochemical investigations, while helping readers to quickly develop the knowledge and skills required to select the appropriate investigations for diagnosis and management, and to correctly interpret test results. Case studies throughout chapters place the information within a clinical context to further assist readers in the development of test-selection and interpretation skills.

Key features include:

• A comprehensive, yet concise overview of the science behind common biochemical investigations
• Helps readers rapidly acquire a fully integrated, practical understanding of biochemical diagnostics
• Full-colour flowcharts and algorithms detailing the rationale for tests, the biochemical processes involved, and test procedures, for quick comprehension and reference
• More clinical cases demonstrating application to practice

Now in its tenth edition, this classic introductory, reference, and revision text is indispensable to medical students, and all those who want to quickly acquire a practical understanding of the scientific principles underpinning biochemical tests and a working knowledge of test selection, test procedures, and the interpretation of results within a clinical context. 

1
Requesting and interpreting tests

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Learning objectives

To understand:

• how sample handling, analytical and biological factors can affect test results in health and disease and how these relate to the concept of a test reference range;
• the concepts of accuracy, precision, test sensitivity, test specificity in the quantitative assessment of test performance.

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Introduction

Biochemical tests are crucial to modern medicine. Most biochemical tests are carried out on blood using plasma or serum, but urine, cerebrospinal fluid (CSF), faeces, kidney stones, pleural fluid, etc. are sometimes required. Plasma is obtained by collecting blood into an anticoagulant and separating the fluid, plasma phase from the blood cells by centrifugation. Serum is the corresponding fluid phase when blood is allowed to clot. For many (but not all) biochemical tests on blood, it makes little difference whether plasma or serum is used.

There are many hundreds of tests available in clinical biochemistry but a core of common tests makes up the majority of tests requested. These core tests are typically available from most clinical laboratories throughout the 24‐h period. Tests are sometimes brought together in profiles, especially when a group of tests provides better understanding of a problem than a single test (e.g. the liver function test profile). More specialist tests may be restricted to larger laboratories or specialist centres offering a national or regional service.

In dealing with the large number of routine test requests, the modern clinical biochemistry laboratory depends heavily on automated instrumentation linked to a laboratory computing system. Test results are assigned to electronic patient files that allow maintenance of a cumulative patient record. Increasingly, test requests can be electronically booked at the ward, clinic or in General Practice via a terminal linked to the main laboratory computer. Equally, the test results can be displayed on computer screens at distant locations, removing the need to issue printed reports.

In this first chapter, we set out some of the principles of requesting tests and of the interpretation of results. The effects of analytical errors and of physiological factors, as well as of disease, on test results are stressed. Biochemical testing in differential diagnosis and in screening is discussed.

Collection of specimens

Test requests require unambiguous identification of the patient (patient’s name, sex, date of birth and, increasingly, a unique patient identification number), together with the location, the name of the requesting doctor and the date and time of sampling. Each test request must specify the analyses requested and provide details of the nature of the specimen itself and relevant clinical diagnostic information. This may be through a traditional request form and labelled specimen or be provided electronically in which case only the sample itself need be sent to the laboratory with its own unique identifier (typically a bar code which links it to the electronic request).

Clinical laboratories have multiple procedures at every step of sample processing to avoid errors. Regrettably, errors do occur and these arise at different stages between the sample being taken and the result being received:

• Pre‐analytical. These arise prior to the actual test measurement and can happen at the clinical or laboratory end. Most errors fall into this category (see Table 1.1).
• Analytical. Laboratory based analytical errors are rare but may occur, e.g. reagent contamination, pipetting errors related to small sample volumes, computing errors.
• Post‐analytical. These are increasingly rare because of electronic download of results from the analyser but include, for example, transcription errors when entering results from another laboratory into the computer manually; results misheard when these are telephoned to the clinician.

Table 1.1Some more common causes of pre‐analytical errors arising from use of the laboratory.

Error	Consequence
Crossover of addressograph labels between patients	This can lead to two patients each with the other’s set of results. Where the patient is assigned a completely wrong set of results, it is important to ...

Table of contents

• Cover
• Title Page
• Table of Contents
• Preface
• List of abbreviations
• About the companion website
• 1 Requesting and interpreting tests
• 2 Disturbances of water, sodium and potassium balance
• 3 Acid–base balance and oxygen transport
• 4 Renal disease
• 5 Disorders of calcium, phosphate and magnesium metabolism
• 6 Diabetes mellitus and hypoglycaemia
• 7 Disorders of the hypothalamus and pituitary
• 8 Abnormalities of thyroid function
• 9 Disorders of the adrenal cortex and medulla
• 10 Investigation of gonadal function infertility, menstrual irregularities and hirsutism
• 11 Pregnancy and antenatal screening
• 12 Cardiovascular disorders
• 13 Liver disease
• 14 Gastrointestinal tract disease
• 15 Nutrition
• 16 Inflammation, immunity and paraproteinaemia
• 17 Malignancy and tumour markers
• 18 Disorders of iron and porphyrin metabolism
• 19 Uric acid, gout and purine metabolism
• 20 Central nervous system and cerebrospinal fluid
• 21 Therapeutic drug monitoring and chemical toxicology
• 22 Clinical biochemistry in paediatrics and the elderly
• Index
• End User License Agreement