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Using tests to help with diagnosis
Preparation for Clinical Skills 1
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Tests that you might hear discussed during clinical skills 1
• 3 patients • Each one illustrates how a clinician can use tests
to help them manage a patient• Some simple questions• Use the information we have already covered• Think about what is going on• Think about how can the test help you as a
doctor to manage a patient • Discussed in greater detail during CS1
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From patient to diagnosis
• 44% Referring GP diagnosis unchanged• 41% Diagnosis changed after history• 7% Diagnosis changed after
examination• 8% Diagnosis changed after
investigation
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Cost of Tests
• Chest X-ray £16.00
• CT chest £56.00
• Full blood count £5.00
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Cost to the patient Equivalent Dose (Sv)
Dose required to sterilise medical products 25 000
Typical total radiotherapy dose to cancer tumour 60
50% survival probability, whole body dose 4
Legal worker dose limit (whole body) 0.02
Average annual dose from all sources in Cornwall 0.008
Average annual dose from natural radiation 0.002
Typical chest X-ray dose 0.00002
Average dose from a flight from UK to Spain 0.00001
Ct scan to abdomen or pelvis delivers about 500 x radiation as a single CXR
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Blood tests
Why do we do them?
1. Screen asymptomatic patients for a disease2. To confirm or refute a diagnosis3. As marker of disease progression / response
to therapy
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What do you get?
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Blood tests
• Blood count• Us and Es• Glucose• HbA1c• Liver function• Cholesterol• Subtypes of cholesterolSpecial blood tests• PSA• Hormones• Thyroid • Virus screens• Cultures for infection
Simple blood tests Also available to GPs
RadiologyECG24 hour ECGEchocardiogram
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Full blood count
Blood count• Hb • Red cell size• White blood cells• Different types of white
blood cells• Platelets
• counts the number of red cells, white cells, and platelets per ml of blood.
• measures the size of the red blood cells and calculates their average (mean) size.
• calculates the proportion of blood made up from red blood cells (the haematocrit).
• measures the amount of haemoglobin in the red blood cells.
• http://www.patient.co.uk/health/Blood-Test-Blood-Count-and-Smear.htm
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Erythrocyte sedimentation rate (ESR)
• Indirect measure of acute phase response• Measures rate of fall of erythrocytes through plasma• Depends on how red cells aggregate• May be disparity between ESR and CRP in certain
conditions
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Blood biochemistry
• Urea• Creatinine
• eGFR• Sodium• Pottasium
• Glucose
• Protein waste• Muscle breakdown
indicates kidney function• Estimated Glomerular
filtration• Blood electrolytes vital for
life and cardiac function• Transportable energy
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Factors affecting urea and creatinine
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C-reactive protein (CRP)
• Acute phase protein• Increases within 6 hours inflammatory
stimulus• Half life 19 hours
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Some examples
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A patient coming for a check up
• Mr Smith • Aged 55 • Visits his GP for
routine check up • What can the GP
offer• Why does he do
this?
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Cholesterol
• The total circulating cholesterol
• Low density ( bad)• High density
(“good”)• Circulating fats
• Total cholesterol – made up of:
• LDL• HDL• Triglycerides
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Other tests
• Liver function
• HbA1c• PSA• Thyroid function• Hormones
• Tests liver function and when it is not working
• Glycosylated Hb – • Released from prostate• Thyroid hormones• Test endocrine function
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Prevention
• What is Primary prevention and what is secondary prevention?
• Can you suggest any examples?
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Reducing risk factors
• What are the risk factors for people with vascular disease?
• How can these be changed and what will the effect be?
• How does a doctor decide what to do and how does this get explained to a patient?
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Mr White – Aged 62 with a history of chest tightness and shortness of
breath
• Which symptoms suggest that a patient has Angina?
• What is happening in an anginal attack?• What can be done to prevent it ?• How do we investigate it?
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Initial tests
• Blood tests
• X ray of chest
• Plain ECG
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Chest x ray
• Aortic knuckle
• Left ventricle
• Pulmonary arteries
• Diaphragm• Air in stomach
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Resting ECG
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Uses of ECG
• Looking at rhythm of the heart
• Information about conduction of electrical impulse
• Information about damage to heart muscle
• Specific patterns of appearance used to help find out about heart, electrolyte changes
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Hyperkalaemia
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The patient is referred to the cardiac clinic
• What can a hospital doctor do?• Exercise ECG• 24 hour ECG for heart rythm• Isotope scans looking at perfusion of heart
muscle• Angiogram to look at blood flow• Echocardiogram
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Exercise ECG – Stress test
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24 hour ECG
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Isotope scans
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Angiography
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Therapeutic intervention
Balloon angioplasty Coronary stent
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Echocardiogram
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Mr Green 63 SUDDEN ACUTE CHEST PAIN
• Which factors on a history suggest that the pain is coming from his heart?
• What is the cause of the pain and what is the process called?
• What are the risks to the patient without prompt treatment?
• What actions can the GP or paramedic at the scene do to reduce the extent of heart muscle damage?
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Cardiac chest pain?
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Acute coronary syndrome ( ACS)
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Pathology in a heart attack
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The patient is seen in the emergency department
• What tests will help to confirm the diagnosis of a heart attack?
• What actions are used to limit the damage to the patients heart
• How are tests used to monitor the patient after the initial event?
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Blood tests
• Troponins – proteins released by damaged muscle into the blood stream
• Levels elevated after 12 hours • May remain elevated for up to 2 weeks
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Chemical markers in Acute coronary syndromes
Blood markers• Troponins – breakdown
products of cardiac muscle cells – suggest cellular damage
• Enzymes – some specific for Cardiac muscle
• CK MB fraction• Some non specific
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ECG in MI
• There are characteristic changes • ECG can record these• Site of changes suggests location of the damage• The shape of the changes may suggest severity of the damage
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Complications of MI.......
• Changes to heart rhythm – slow, fast, very fast.......
• Loss of pump function• Leaking of valves• Blood clots• Drop in blood pressure• Failure of heart pump
ECG monitoring.......
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A medical emergency
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Thrombolysis and primary angioplasty
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