1. An Introduction to blood tests
Nick Leaver
5th year medical student

2. Learning outcomes Learn the components of various blood tests
Learn basic interpretation
Learn how they can aid formulation of a diagnosis and be used to guide further management
Clinical cases (previous UoL exam questions)

3. Blood tests FBC VBG U&E ABG LFT Blood glucose CRP INR ESR Cholesterol
TFT
Blood film
Cross match
Group & Save
Cancer blood tests
Rheumatological markers
VBG
ABG
Blood glucose
INR
Cholesterol
Coagulation screen
Blood culture
Thrombophilia screen
Genetic testing
Hepatitis serology
CD4 count - HIV

4. FBC Full blood count: White cell count Red cell count Haemoglobin
Haematocrit
Mean Cell Volume
MCH
MCHC
Red cell distribution width
Platelets
Differential white cell count
Neutrophils, lymphocytes, monocytes, basophils, eosinophils

5. Hb & MCV Haemoglobin Mean Corpuscular (Cell) volume
Oxygen carrying molecule
Mean Corpuscular (Cell) volume
The average diameter of the red blood cells
Becomes important when classifying anaemias

6. Anaemia
Definition: low haemoglobin concentration and may be due to a low red cell mass or increased plasma volume
Classified by low Hb (<135g/L men, <115g/L women)
Microcytic
-MCV low
Causes
Iron deficiency
Thalassaemia
Sideroblastic
Normocytic
-MCV normal
Causes
Anaemia of chronic disease
Renal failure
Pregnancy
Macrocytic
-MCV high
Causes
B12 or folate deficiency
Alcohol excess
Cytotoxic drugs
Bone marrow infiltration
Hypothyroidism
Haemolysis

7. WCC White cell count Differential white cell count
High WCC – Infection, inflammation, cancer
Low WCC – chronic infection, decompensation after fulminant infection, bone marrow failure, chemotherapy, HIV
Differential white cell count
Neutophils – bacterial infection
Lymphocytes – viral infection
Eosinophils – raised in allergy (e.g. asthma)
Monocytes
Basophils

8. Platelets ‘Thrombocytes’ Involved in clotting
Low platelets – Thrombocytopenia
Infections, inflammation
Idiopathic thrombocytopenic purpura (ITP)
Drug induced – including heparin (HIT)
Blood malignancies
Raised platelets – Thrombocytosis
Reactive – (infection, inflammation, malignancy, acute blood loss)

9. U&E
Urea and Electrolytes
Sodium
Potassium
Urea
Creatinine
eGFR

10. eGFR estimated Glomerular Filtration Rate
Gives an ESTIMATE of kidney function based on GENERIC factors

11. Urea and Creatinine Urea Creatinine
Important for the metabolism of nitrogen containing compounds
Freely filtered at the glomerulus but is reabsorbed
Creatinine
Levels remain constant if renal function is stable
Freely filtered at the glomerulus and not reabsorbed
Raised creatinine is a marker of renal injury

12. Electrolytes Sodium Potassium Low (hyponatraemia)
Dilutional
Vomiting and diarrhoea
Diuretics (especially thiazide)
High (hypernatraemia)
Hypovolaemia
Diabetes insipidus
Potassium
Low (hypokalaemia)
Diuretics
Alkalosis
High (Hyperkalaemia)
AKI/CKD
Spironalactone, ACEi, NSAIDs, heparin
Acidosis
The main risk of deranged potassium is arrythmias

13. AKI Acute Kidney Injury Defined as
Rapid reduction in kidney function
Defined as
Increase in Creatinine by >26.5 μmol/l within 48h
Increase in Creatinine to >1.5 times baseline, within 7 days
Urine volume < 0.5 ml/kg/h for 6 hours
Most common causes are hypovolaemia, sepsis, drugs

14. CKD Chronic Kidney Disease GFR <60 for 3 months with symptoms/signs
5 stages
Stage 1 GFR >90
Stage 2 GFR 60-89
Stage 3 GFR 30-59
Stage 4 GFR 15-29
Stage 5 GFR <15
Causes include hypertension, diabetes, glomerulonephritis, urological obstruction, autoimmune

15. LFT Liver function tests Gamma-Glutamyl Transferase (GGT)
Alanine aminotransferase (ALT)
Aspartate aminotransferase (AST)
Alkaline Phosphatase (ALP)
Bilirubin
Albumin

16. ALP & GGT
ALP
An enzyme found predominantly in the bile ducts and bones
Raised in bone disease or biliary tract obstruction
GGT
An enzyme involved in the conversion of glutathione to an amino acid
Raised in acute alcohol intake
Predominantly used as a marker for disease of the biliary tract

17. ALT and AST Found in the hepatocellular cells of the liver
The most sensitive marker of hepatocellular injury
Can work out the ratio to determine pathology of the hepatocellular injury

18. Bilirubin Breakdown product of heme Excreted in bile and urine
Conjugated with glucuronic acid in the liver
Raised in biliary obstruction and hepatocyte damage

19. Biliary tract disease made easy
4 biliary tract diseases can be easily identified and differentiated on routine blood tests for exams (it doesn’t always work in real life)
Use the test which is most raised (“-” doesn’t mean negative)
AST/ALT
ALP
GGT
Bilirubin
CRP
Signs of infection
Biliary colic -
Cholecystitis +
Choledocholithiasis
-/+ ++
Ascending cholangitis

20. Case 1
A 10 year old boy presents to the ED with a 6 month progressive history of SOB.
Differential diagnoses
Asthma, sinusitis, tonsillitis, anaemia, pneumonia, pneumothorax, pulmonary fibrosis, cardiac failure, allergy, medication, vasculitis, anxiety, acid reflux, sleep apnoea, obesity, genetic diseases, cancer
Full blood count:
White cell count 8.0 ( )
Haemoglobin 145 ( )
Mean Cell Volume 92.5 ( )
Platelets 227 ( )
Neutrophils 3.5 ( )
Lymphocytes 3.7 ( )
Monocytes 0.7 ( )
Basophils 0.1 ( )
Eosinophils 3.5 ( )
Diagnosis
Asthma

21. Case 2
A 28 year old female presents with a 3 month history of feeling tired all the time. She has no past medical history.
Full blood count:
White cell count 8.0 ( )
Haemoglobin 100 ( )
Mean Cell Volume 72.5 ( )
Platelets 227 ( )
Neutrophils 3.5 ( )
Lymphocytes 3.7 ( )
Monocytes 0.7 ( )
Basophils 0.1 ( )
Eosinophils 0.1 ( )
Further blood tests:
U&Es (Normal), TFT (Normal), HbA1c (Normal)
Diagnosis:
Iron deficiency anaemia
Most commonly due to menstruation

22. Case 3
A 57 year old male was found confused on the floor outside the doorway of a shopping centre. You are unable to elicit a history.
Full blood count:
White cell count 8.0 ( )
Haemoglobin 100 ( )
Mean Cell Volume 120 ( )
Platelets 227 ( )
Neutrophils 3.5 ( )
Lymphocytes 3.7 ( )
Monocytes 0.7 ( )
Basophils 0.1 ( )
Eosinophils 0.1 ( )
Liver function tests
ALT 210 (0-49)
ALP 120 (30-130)
GGT 2440 (0-59)
Bilirubin 12 (0-20)
Albumin 36 (35-50)
Diagnosis
Acute alcohol intoxication

23. Case 4
An 82 year old female is admitted to hospital on Friday for a routine operation due to happen on Tuesday. Her routine blood tests are performed on Monday.
Urea and Electrolytes
Friday Monday
Sodium ( )
Potassium ( )
Urea ( )
Creatinine (53-97)
eGFR (<90)
What has happened
Developed Acute Kidney Injury
Why
Lack of fluid prescribing? Patient not drinking? New drugs? Sepsis?

24. Case 5
A 40 year old female presents to the GP with jaundice for 3 days and RUQ pain. She has spasms of pain which are worse after eating. She has no symptoms of fever.
Clinical diagnosis
Choledocholithiasis
Liver function tests
ALT 479 (0-49)
ALP 620 (30-130)
GGT 699 (0-59)
Bilirubin 68 (0-20)
Albumin 38 (35-50)
CRP 4 (0-4)
Diagnosis

25. References Davidsons Principles and Practice of Medicine
Oxford handbook of clinical haematology
Traynor J et al. How to measure renal function in clinical practice. BMJ 333 (7571):

26. Any Questions?