Blood Results in Clinical Practice: A practical guide to interpreting blood test results

2nd Edition

Graham Basten

• Publisher: M&K Update
• Year: 2019
• ISBN:
  9781910451663
• Topic: Medicine
• Subtopic: Hematology

This book was originally written after feedback suggested that storytelling was very helpful to students and practitioners wanting to remember blood tests and their implications. Each section, where appropriate, therefore contains a 'story', as well as an overview of the relevant anatomy, physiology and biochemistry. This revised, updated edition continues to use storytelling to aid understanding, and introduces a unique 10-point system to help explain blood results. The use of storytelling has also been significantly improved and refined, following several years of feedback on the first edition. Less formal than a biochemistry textbook and containing more narrative than an online protocol, Blood Results in Clinical Practice provides an excellent, accessible introduction to blood tests and what they mean. It also enables advanced practitioners to reflect on and improve their practice; and includes new and updated sections of relevance to physiotherapists, paramedics, pharmacists and advanced nurse practitioners. Finally, it provides a resource for patients and their relatives who may be keen to know more about the meaning and function of particular blood tests.

1

Blood results made easy

This book will enable you to:

•Understand how blood is split into chemicals (biochemistry) and cells (haematology)

•Look for patterns using family groups

•Consider how blood tests can change cellular content, waste products, production and interaction

•Be more confident when identifying and managing ‘out of range’ and ‘in range’ blood tests in a symptomatic patient

•Consider four questions when interpreting the blood result:

•How far out of range is it?

•Do we have a clinical decision limit or protocol?

•Does the result make sense?

•Does the family group support the result?

•Determine the importance of what is being measured, understand why and when it was requested, and know what to do next with the result?

‘Storytelling’

I’d like you to imagine that you are not a healthcare professional, student, client or patient. Instead, imagine that you are a famous detective. (Any will do – you decide.) You have arrived at a crime scene and you will look at various pieces of evidence (symptoms) and will hear several witness statements. Each witness statement represents a blood test result. With each statement, you need to ask:

•How reliable is the witness?

•When was the statement taken?

•Does it make sense?

•How close was the witness to the crime scene?

•Most importantly do their ‘mates’, friends or associates back up the story?

(If we get corroborated statements all saying the same thing, we can usually place greater confidence in them.)

We will return to this approach throughout the book.

Key themes

In this section we will explore key themes to help interpret blood test results. As we interpret the blood test results, we can consider some initial questions.

What are we measuring?

If we know what the blood test is actually measuring, that should help us understand the ‘so what’ question. Is it a cell or a chemical? We can split blood tests into two types – biochemistry and haematology. The former measure all the chemicals in the blood, while the latter measure all the cells in the blood. The biochemistry tests measure liver function, kidney function, inflammation, thyroid, autoimmune and are generally more closely associated with urgent ‘red flag’ conditions like hyperkalaemia – raised potassium (K). The haematology tests measure cells and report on the types of cells, how many there are and how big they are. This is very useful when we are looking at patterns of anaemia and infection, and ‘red flag’ conditions like myeloma and leukaemia. (This is all covered in more detail in Chapter 5.)

To learn more about how to separate the blood into these two components, see the section on ‘Blood collection’ (p. 5) and check local phlebotomy protocols.

Why did we measure it?

Some thoughts under this theme:

•Was the patient symptomatic and did we specifically request the blood test to confirm our thinking?

•Is the result incidental? For example, if the patient is asymptomatic, did they have a routine health screen or pre-operative assessment which highlighted an out-of-range result?

•Are we requesting the blood test as part of a triage exclusion service?

•Is this part of normal pathology management such as drug or disease monitoring?

When did we measure it?

Some thoughts under this theme:

•Did we measure this blood test on a hospital ward 10 minutes ago? Or was it measured in primary care three months ago? (There may be good reasons for both these scenarios.)

•Have the patient’s results always been raised or decreased? Despite being out of the normal range, is your patient ‘normal’ for their cohort?

What do we do next with the result?

Think about the following:

•Do we have a protocol or clinical decision flow chart for results which are out of range?

•What is my remit – to treat or to refer?

•When do I file as ‘normal’?

•When do I escalate or de-escalate?

We can summarise these as four key questions.

Question 1 – How far out of range is it?

Consider:

•What is normal in your setting?

•What’s the biggest or smallest result you’ve seen in your setting?

•Do you have clinical limits (see later chapters)?

•Is it always slightly out of range?

•Is it within a range or group that could contain false positive results (see later chapters)?

Question 2 – Does the result make sense?

Consider:

•Has the patient just had an operation?

•Has the patient been started on medication?

•Do they have symptoms?

•In short, do the results match the person in front of you?

Question 3 – What do the family groups tell us? Do they all agree?

See Chapter 3 for more detail on family groups.

Question 4 – Is this an important blood test?

Consider:

•Which are the ‘go to’ blood tests in your setting, the ones that people get worried about?

•Some tests are more important than others. Ask yourself what would be the consequences of me filing this one, versus taking action?

•For some tests (such as potassium), we would usually follow up; but for haematocrit we probably wouldn’t. One is very important and dangerous, the other less so.

Reading the result

All blood test results will have a similar layout and should contain:

•The patient or client identification code or number

•The person who requested the blood

•The test or investigation (take care with this one, as abb...