Blood Results in Clinical Practice

• Publisher: M&K Publishing
• Year: 2013
• ISBN:
  9781907830730
• Topic: Medicine
• Subtopic: Internal Medicine & Diagnosis

This book was written after feedback suggested that stories and analogies were very helpful to students wanting to remember blood tests and their implications. For this reason each section, where appropriate, contains an analogy, in addition to an overview of the relevant anatomy, physiology and biochemistry. The book links tests and conditions, and gives strategies for clinical practice using simple language.It will be useful as a supplementary text for those studying nursing, healthcare and medicine. It will also provide a quick-reference handbook for working healthcare professionals. Finally, it will provide a resource for patients and their relatives who may be keen to know more about the meaning and function of a particular blood test.

1

Understanding blood tests

This book will enable you to:

• Appreciate the importance of blood tests in diagnosis and patient management

• Augment your current knowledge by defining what each test is, and explaining what it shows from a physiological and biochemical viewpoint

• Understand the many abbreviations used in blood tests (see Table 1)

• Work through the case study presented in Chapter 2, and then seek additional relevant case studies from the Further Reading section and local sources

• Determine the clinical significance of values outside the reference range, or indeed of an ill person with normal results

• Develop linking of tests and using tests for exclusion

• Try out the strategy example in Chapter 2, adapting it to your own clinical setting

• Explore how tests form a natural hierarchy, with full blood count (FBC), urea and electrolytes (U&Es) and liver function tests (LFTs) being common first-line tests, which may then justify more specific (and often more expensive) tests.

Quick reference glossary

The following table shows common terms, abbreviations and some typical observations relating to the various blood tests. Some examples also have metaphors, shown in quotation marks, to aid memory and understanding. These will be explained further in the corresponding chapters.

Table 1.1: Glossary of terms used in blood tests

Full blood count (FBC)
Platelet	• Cell that causes the blood to clot • Also a marker of bone marrow function • Decreased in some leukaemia and myelomas • Additional test is mean platelet volume (MPV)
White blood cell count (WBC)	• The total number of white cells in the blood
Neutrophil	• A type of white blood cell • Responds to tissue damage via C-reactive protein (or CRP) • Raised in bacterial infections, autoimmune conditions • ‘The fire engine’
Lymphocyte	• A type of white blood cell • Makes antibodies • Raised in viral infections and some myelomas • ‘The police’
Monocyte	• A type of white blood cell • Infiltrates the tissue in systemic bacterial infections • Linked to cardiovascular disease and high low-density lipoprotein (LDL) cholesterol • ‘The miner’
Basophil	• A type of white blood cell • Important in allergic responses and hypersensitivity
Eosinophil	• A type of white blood cell • Important in allergic responses and hypersensitivity
Blast/Atypical	• A type of dysfunctional white cell • Raised in leukaemia and myelomas
Haematocrit (Hct)	• Percentage of red blood cells in the whole blood • Decreased in anaemia • Elevated in polycythaemia
Haemoglobin (Hb)	• The oxygen-carrying protein in the red blood cell • Decreased in anaemia • Elevated in polycythaemia
Red blood cell count (RBC)	• The total number of red blood cells in the blood as a count • Decreased in anaemia • Elevated in polycythaemia
Mean cell volume (MCV)	• The average size of the red blood cells • Low in iron deficient anaemia • Normal in blood loss anaemia • High in folate and B12 deficient anaemia
Inflammatory markers
Plasma viscosity (PV)	• A measure of more ‘stuff’ in the blood • Thus, a surrogate, non-specific marker of • inflammation • Increased in autoimmune conditions, infection, cell damage, cancer, myelomas • ‘The traffic jam due to fire engines and police (white cells)’ • Could remain raised for two weeks post-injury, as increased white cells have around two-week lifespan
Erythrocyte sedimentation rate (ESR)	• How quickly red blood cells fall in a tube, in a lab • A surrogate, non-specific, marker of inflammation that has elicited a fibrinogen response • Fibrinogen ‘sticks’ red blood cells together so they become heavier and fall more quickly • Could be normal in low damage inflammation as seen in some autoimmune conditions • ‘The scaffolding and building-supporting structure following a large fire’ • If raised, could remain raised for a significant time post-event
C-reactive protein (CRP)	• A chemo-attractant protein released in response to tissue damage • ‘The fire alarm’ • Possible to miss the CRP response post-injury whilst still having raised PV and ESR • Increasingly being used as a sensitive marker for atherosclerotic vascular damage to indicate cardiovascular risk
Urea and electrolytes (U&Es), Kidney function
Sodium (Na)	• Extracellular electrolyte that controls water balance and blood pressure • Raised in dehydration, urea
Potassium (K)	• Intracellular electrolyte, controls cellular pumps and receptors via electric potential • Therefore a red flag if in high concentrations in the blood
Urea	• A marker of acute renal dysfunction, such as distress, although this could be something like dehydration, so to Na levels
Creatinine	• A marker of chronic renal function, such as a renal stone
Estimated glomerular filtration rate (eGFR)	• A general marker of kidney function • Used to diagnose chronic kidney disease staging • Used to confirm renal dysfunction as cause of other conditions such as renal anaemia
Liver function tests (LFTs)
Alanine aminotransferase (ALT)	• A liver enzyme • Often raised in trauma, drug toxicity, and viral hepatitis
Aspartate aminotransferase (AST)	• A liver enzyme • Often raised in trauma, acute alcohol hepatitis and liver failure • Also found in the heart so to cardiac markers/chest pain
Gamma-glutamyl transferase (GGT)	• A liver enzyme • Often raised following alcohol intake • to RBC, MCV and folate to differentiate between alcohol, B12 and diabetes neuropathies
Alkaline phosphatase	• A liver enzyme • Often increased in biliary tree damage such as gallstones Also found in the bone (check Ca), kidney (check • U&Es) and placenta (check age and gender)
Amylase	• A liver enzyme • Often increased in pancreatitis and pancreatic tumours
Bilirubin	• A marker of the ‘plumbing’ of the liver • Increased in jaundice, usually caused by pre-, actual or post-hepatic blockage
Urobilinogen	• A bilirubin breakdown product, usually absent in post-hepa...