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Hypertension


THE INVESTIGATION OF HYPERTENSION
THE INVESTIGATION OF HYPERTENSION
Definition
Hypertension is defined by the WHO criteria as a systolic BP of = 160 mm Hg, or a diastolic BP = 95 mm Hg.
The majority (70-90%) of hypertensive patients have essential (primary) hypertension.
Renal disease (renal vascular disease and chronic renal failure) is the major cause of secondary hypertension.
Hypertension of any aetiology may induce or aggravate renal insufficiency.
Endocrine disease is a minor, but important cause of secondary hypertension in relatively young people
Renal disease
A diagnosis of essential hypertension cannot be made before clinical, laboratory and radiological examination have excluded secondary causes. The costs of initial laboratory investigations should be seen in the light of the lifelong need for antihypertensive therapy and/or for long-term supervision of blood pressure. The aim of initial laboratory investigation of hypertensive patients is:
  • To detect associated risk factors
    1. Hyperlipidaemia
    2. Diabetes mellitus
    3. Hyperuricaemia
  • To provide a baseline level for serum components which may be adversely affected by antihypertensive therapy (e.g. glucose, potassium, urate)
  • To detect evidence of target organ damage (e.g. kidneys)
  • To exclude secondary causes of hypertension
Hence BASIC studies should be performed in all patients with sustained hypertension. These include:
  1. FBC
  2. U & E, creatinine
  3. Blood glucose
  4. Cholesterol and triglycerides
  5. Calcium, phosphate
  6. Uric acid
  7. GammaGT
  8. Urine microscopy and chemistry
CAUSES
SPECIFIC LABORATORY TESTS
RENAL DISEASES
ENDOCRINE DISEASE
Mineralocorticoid excess syndrome
Cushing's syndrome
Phaeochromocytoma
SECONDARY STUDIES should be performed if:
  • from the initial evaluation a secondary form of hypertension is suggested:
    1. Abrupt onset of severe hypertension
    2. Onset of hypertension of any severity in patients < 25 years or > 50 years of age
    3. Examination reveals abdominal bruit or bilateral upper abdominal masses
    4. Basic laboratory tests reveal:
      1. Evidence of renal disease
      2. Hypokalaemia
      3. Hyperglycaemia
      4. Hypercalcaemia
and / or
  • hypertension is not controlled after initial therapy.

SECONDARY STUDIES should include:
Blood (erect sample, afternoon sample) for:
  • Cortisol
  • Creatinine
  • Sodium and potassium
  • Urine (24 hour urine for all the below tests):
    • Catecholamines/metanephrines
    • Cortisol
    • Creatinine clearance
    • Sodium and potassium (if hypokalaemia)
Investigation for SPECIFIC secondary causes - if the results obtained from the SECONDARY STUDIES suggest a particular pathology then further investigation is suggested.
SPECIFIC SECONDARY CAUSES LABORATORY INVESTIGATIONS
RENOVASCULAR HYPERTENSION
24 hour urine for aldosterone

08h00 supine renin and aldosterone
10h00 erect renin and aldosterone
PHAECHROMOCYTOMA
24 hour urine for catecholamines

(3 studies are advocated before phaeochromocytoma can be confidently excluded).
CUSHING'S SYNDROME
24 hour urine for cortisol

Afternoon (pm) cortisol
Overnight dexamethasome suppression test.
(administer 1 mg of dexamethasone per os at 23h00, and measure cortisol between 07h00 and 09h00 the following morning)
PRIMARY HYPERALDOSTERONISM
24 hour urine for aldosterone
08h00 supine renin and aldosterone
10h00 erect renin and aldosterone
Initial laboratory investigations
A diagnosis of essential hypertension cannot be made before clinical, laboratory and radiological examination have excluded secondary causes. The costs of initial laboratory investigations should be seen in the light of the lifelong need for antihypertensive therapy and/or for long-term supervision of blood pressure.
The aim of initial laboratory investigation of hypertensive patients is:
  • To detect associated risk factors
    1. Hyperlipidaemia
    2. Diabetes mellitus
    3. Hyperuricaemia
  • To provide a baseline level for serum components which may be adversely affected by antihypertensive therapy (e.g. glucose, potassium, urate)
  • To detect evidence of target organ damage (e.g. kidneys)
  • To exclude secondary causes of hypertension
Hence BASIC studies should be performed in all patients with sustained hypertension. These include:
1. FBC
2. U & E, creatinine
3. Blood glucose
4. Cholesterol and triglycerides
5. Calcium, phosphate
6. Uric acid
7. GammaGT
8. Urine microscopy and chemistry
References
 
Harrison 's Principles of Internal Medicine. 12 th Edition. 1001 - 1015
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