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Interpreting blood tests and the ECG: practical risk assessment
Dr T S Dhanjal PhD MRCP
Cardiovascular courses29th October 2008
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Aims of the talk
• Understand why we do blood tests.
• What to the blood tests mean?
• The importance of risk stratification.
• The Electrocardiograph (ECG).
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Why investigate ?
• To detect the secondary causes of hypertension.
• Assess for the consequences of hypertension.
• Risk stratification to determine overall cardiovascular risk.
• Monitoring of treatment.
• Detection of disease association.
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Detection of secondary hypertension
Serum Potassium
Low Lowish Normal High
Hyperaldosteronism
Renal FailurePrimary (Conn’s) Secondary (RAS)
3.7 – 5.2 mEq/l3.7 – 4.0
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Biochemical Conn’s
Secondary hyperaldosteronism(RAS, renin secreting tumours)
Liquorice(11 DHD inhibitor)
Liddle’s syndrome
Potassium Sodium Renin Aldosterone
Conn’s syndrome
Serum measurements
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Hyperkalaemia
• May develop in Renal Failure.
• Drugs– ACE I– ARBs– Potassium sparing
diuretics
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Serum Sodium
• High / highish– Primary hyperaldosteronism
• Low / lowish– Secondary hyperaldosteronism (Malignant
Hypertension or renal disease)– Diuretic overuse
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Urea & Creatinine
• Creatinine– breakdown product of creatine phosphate in muscle.– usually produced at a fairly constant rate by the body.– Filtered by the kidney and not re-absorbed.– If the filtering of the kidney is impaired then blood levels
will rise.– Used to determine Creatinine Clearance which
estimates the Glomerular Filtration Rate (GFR).
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Monitoring Creatinine levels
• Isolated essential hypertension rarely results in renal impairment.
• But concomitant disease (diabetes) or treatment (ACE I / ARB) can exacerbate.
• Intrinsic renal disease can cause hypertension.
• Serum creatinine only rises with marked damage to nephrons so not a good test to detect early stage kidney disease.
• Problem with measuring creatinine clearance is a 24 hour urine collection is required.
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Is eGFR the answer ?
• NSF for renal sevices requires laboratories to estimate GFR using the MDRD formula.
• Fundamentally based on serum creatinine measurments so why should it be any better?
• Just as sensitive as measuring serum creatinine over time.
• BUT variability of eGFR increases as actual GFR improves.
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Poggio et al 2005
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Reciprocal creatinine chart
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Blood Glucose
• Type 2 DM increases risk of cardiovascular, renal, retinal and neuropathic complications.
• Screen in hypertensive patients:– Random glucose > 11.1 mmol/l.– OGTT.
• Is it more important to aggressively control hypertension ?– UKPDS trials
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Other serum biochemical tests
• Uric acid– 40% of patients with hypertension.– Increased with alcohol, thiazide diuretics.
• Liver function tests– Excess alcohol intake.– Steatohepatitis – diabetes, metabolic syndrome.
• Serum calcium– Hypocalcaemia secondary to CRF.– Hypertension associated with 1˚ Hyperparathyroidism.– Hypercalcaemia also associated with thiazide
diuretics.
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24 hour urine collection
• Young, thin patients with paroxysmal symptoms.
• Urinary metanephrines.– Metabolite of epinephrine created by action of
catechol-O-methyl transferase on epinephrine.
• Creatinine Clearance using the Cockroft & Galt formula.
• Sodium excretion to quantify salt intake.
• Degree of proteinuria - renal biopsy ?
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Pheochromocytoma
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Haematology
• Detection of polycythaemia– Raised RBC, Hb & RBC volume.– Primary (PCV) or secondary (hypoxia).– Gaisbok’s syndrome.
• Mean Cell Volume– Increased by alcohol and hypothyroidism.
• Connective tissue disease– Platelets, ESR, autoimmune antibodies etc.
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Lipid profile
• For assessment of cardiovascular risk.
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Cardiovascular risk assessment
• JBS 2: Joint British Societies' guidelines on prevention of cardiovascular disease in clinical practice, Heart, 2005.
• Prepared by: British Cardiac Society, British Hypertension Society, Diabetes UK, HEART UK, Primary Care Cardiovascular Society, The Stroke Association.
• The specific objective to reduce the risk of CVD and its complications in high risk patients.
• 3 categories:– Any form of established atherosclerotic CVD.– Diabetes mellitus (type 1 or 2).– Asymptomatic people without established CVD but who have a
combination of risk factors which puts them at high total risk (estimated multifactorial CVD risk 20% over 10 years) of developing atherosclerotic CVD for the first time.
Measure total cholesterol AND HDL
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Prepared by: British Cardiac Society, British Hypertension Society, Diabetes UK, HEART UK, Primary Care Cardiovascular Society, The Stroke Association, Heart 2005;91:v1-v52
Joint British Societies' cardiovascular disease (CVD) risk prediction chart: non-diabetic men.
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Assessment of end-organ damage
• Kidneys– Urinalysis.
• Microvasculature– Retinopathy.
• Heart– ECG.– Echocardiography.
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Left Ventricular Hypertrophy
• LVH is one of the earliest manifestations of hypertensive heart disease.
• Leads to diastolic dysfunction and heart failure secondary to systolic dysfunction.
• Other cardiac complications:– Myocardial Infarction.– Atrial Fibrillation
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Electrocardiographic assessment of LVH (1)
Sokolow-Lyon index:There are two criteria with these widely used indices:* Sum of S wave in V1 and R wave in V5 or V6 >/= 3.5 mV (35 mm)and/or* R wave in aVL >/= 1.1 mV (11 mm)
Cornell voltage criteria – These more recent criteria are based upon echocardiographic correlative studies designed to detect a left ventricular mass index >132 g/m2 in men and >109 g/m2 in women.For men: S in V3 plus R in aVL >2.8 mV (28 mm) For women: S in V3 + R in aVL >2.0 mV (20 mm)
Cornell voltage-duration measurementQRS duration×Cornell Voltage > 2440 ms × mV
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Electrocardiographic assessment of LVH (2)
Sensitivity and specificity for selected ECG criteria of LVH
CriterionSensitivity
(%)Specificity
(%)
Sokolow Lyon Voltage 22 100
Cornell Voltage Criteria 42 96
Cornell Voltage Duration Criteria
51 95
RaVL > 11 mm 11 100
Romhilt-Estes > 4 points 54 85
Romhilt-Estes > 5 points 33 94
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Summary
Potassium Diuretics, renal disease, Conn’s.
Sodium Primary hyperaldosteronism.
Creatinine Monitor renal function.
Glucose Screen for diabetes mellitus.
Urate Diuretics, alcohol.
LFTs Alcohol.
Calcium Primary hyperparathyroidism
Total Cholesterol / HDL
Calculate cardiovascular risk.
Haemoglobin Polycythaemia, CRF.
Mean cell volume Alcohol.
Platelets Connective tissue disease.
Urinalysis Proteinuria, Haematuria, Glycosuria.
ECG Left ventricular hypertrophy.