Download An Introduction to blood tests

An Introduction to blood tests
Nick Leaver
5th year medical student
www.peermedics.com
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)
Blood tests
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FBC
U&E
LFT
CRP
ESR
TFT
Blood film
Cross match
Group & Save
Cancer blood tests
Rheumatological markers
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VBG
ABG
Blood glucose
INR
Cholesterol
Coagulation screen
Blood culture
Thrombophilia screen
Genetic testing
Hepatitis serology
CD4 count - HIV
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
Hb & MCV
• Haemoglobin
– Oxygen carrying molecule
• Mean Corpuscular (Cell) volume
– The average diameter of the red blood cells
– Becomes important when classifying anaemias
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
Macrocytic
-MCV high
• Causes
Normocytic
-MCV normal
• Causes
– Anaemia of
chronic disease
– Renal failure
– Pregnancy
– B12 or folate
deficiency
– Alcohol excess
– Cytotoxic drugs
– Bone marrow
infiltration
– Hypothyroidism
– Haemolysis
WCC
• 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
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–
–
–
–
Neutophils – bacterial infection
Lymphocytes – viral infection
Eosinophils – raised in allergy (e.g. asthma)
Monocytes
Basophils
Platelets
• ‘Thrombocytes’
• Involved in clotting
– Low platelets – Thrombocytopenia
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•
•
•
Infections, inflammation
Idiopathic thrombocytopenic purpura (ITP)
Drug induced – including heparin (HIT)
Blood malignancies
– Raised platelets – Thrombocytosis
• Reactive – (infection, inflammation, malignancy, acute
blood loss)
U&E
• Urea and Electrolytes
– Sodium
– Potassium
– Urea
– Creatinine
– eGFR
eGFR
• estimated Glomerular Filtration Rate
– Gives an ESTIMATE of kidney function based on
GENERIC factors
Urea and Creatinine
• Urea
– 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
Electrolytes
•
Sodium
– Low (hyponatraemia)
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Dilutional
Vomiting and diarrhoea
Diuretics (especially thiazide)
– High (hypernatraemia)
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Hypovolaemia
Diabetes insipidus
Potassium
– Low (hypokalaemia)
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Diuretics
Alkalosis
– High (Hyperkalaemia)
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AKI/CKD
Spironalactone, ACEi, NSAIDs, heparin
Acidosis
– The main risk of deranged potassium is arrythmias
AKI
• Acute Kidney Injury
• 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
CKD
• Chronic Kidney Disease
– GFR <60 for 3 months with symptoms/signs
– 5 stages
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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
LFT
• Liver function tests
– Gamma-Glutamyl Transferase (GGT)
– Alanine aminotransferase (ALT)
– Aspartate aminotransferase (AST)
– Alkaline Phosphatase (ALP)
– Bilirubin
– Albumin
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
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
Bilirubin
• Breakdown product of heme
• Excreted in bile and urine
• Conjugated with glucuronic acid in the liver
• Raised in biliary obstruction and hepatocyte
damage
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
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-
-
-
-
-
Cholecystitis
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-
-
-
+
+
Choledocholithiasis
-/+
++
+
++
-
-
Ascending
cholangitis
+
++
+
++
++
++
Case 1
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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:
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White cell count
Haemoglobin
Mean Cell Volume
Platelets
Neutrophils
Lymphocytes
Monocytes
Basophils
Eosinophils
Diagnosis
– Asthma
8.0
145
92.5
227
3.5
3.7
0.7
0.1
3.5
(3.9-11.1)
(115-165)
(78.2-101.0)
(150-450)
(1.8-7.5)
(1.0-4.0)
(0.0-1.0)
(0.0-0.2)
(0.0-0.4)
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:
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–
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White cell count
Haemoglobin
Mean Cell Volume
Platelets
Neutrophils
Lymphocytes
Monocytes
Basophils
Eosinophils
8.0
100
72.5
227
3.5
3.7
0.7
0.1
0.1
(3.9-11.1)
(115-165)
(78.2-101.0)
(150-450)
(1.8-7.5)
(1.0-4.0)
(0.0-1.0)
(0.0-0.2)
(0.0-0.4)
• Further blood tests:
– U&Es (Normal), TFT (Normal), HbA1c (Normal)
• Diagnosis:
– Iron deficiency anaemia
• Most commonly due to menstruation
Case 3
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•
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:
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•
8.0
100
120
227
3.5
3.7
0.7
0.1
0.1
(3.9-11.1)
(115-165)
(78.2-101.0)
(150-450)
(1.8-7.5)
(1.0-4.0)
(0.0-1.0)
(0.0-0.2)
(0.0-0.4)
210
120
2440
12
36
(0-49)
(30-130)
(0-59)
(0-20)
(35-50)
Liver function tests
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White cell count
Haemoglobin
Mean Cell Volume
Platelets
Neutrophils
Lymphocytes
Monocytes
Basophils
Eosinophils
ALT
ALP
GGT
Bilirubin
Albumin
Diagnosis
–
Acute alcohol intoxication
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
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Sodium
Potassium
Urea
Creatinine
eGFR
Friday
Monday
139
5.1
6.5
88
71
142
5.6
13.2
150
31
(133-146)
(3.5-5.3)
(2.8-7.8)
(53-97)
(<90)
• What has happened
– Developed Acute Kidney Injury
• Why
– Lack of fluid prescribing? Patient not drinking? New drugs? Sepsis?
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
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–
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ALT
ALP
GGT
Bilirubin
Albumin
– CRP
479
620
699
68
38
(0-49)
(30-130)
(0-59)
(0-20)
(35-50)
4
(0-4)
• Diagnosis
– Choledocholithiasis
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): 733-737
Any Questions?
www.peermedics.com