Investigating the Endocrine System Flashcards
Types of hormone
Peptide (e.g PTH, ACTH, TSH)
Steroid (e.g. Testosterone, Oestradiol, Cortisol)
Tyrosine-based (e.g. T3, T4)
TBG
Carries thyroid hormone but only unbound forms are physiologically active
If level of TBG changes, this results in a change in the level of the free hormones
Therefore measurement of total hormone levels can be misleading
Causes of increased TBG
Genetics
Pregnancy
Oestrogens
Causes of decreased TBG
Genetics Protein-losing status Malnutrition Malabsorption Acromegaly Cushing's High dose corticosteroids Severe illness Androgens
Low TSH, low thyroxine
Pituitary failure
Low TSH, high thyroxine
Thyroid gland overproduction (e.g. Graves’)
High TSH, low thyroxine
Unresponsive thyroid
High TSH, high thyroxine
Pituitary gland overproduction or feedback fails (rare)
“Sick euthyroid disease”
No point in measuring thyroid hormones in critically unwell patients - will be all over the place and difficult to interpret
Repetition of TFTs (guidelines)
Repeat every 3 years in healthy patients (unlikely)
Graves’ - 1-2 months after radioactive iodine, then 4-6 week intervals if remain thyrotoxic, or 6-8 weeks following thyroidectomy
Hypothyroidism - 2 months, but not before this due to lag period of thyroxine, if stabilised, then annually
Immunoassays
Use of monoclonal antibodies
Alternative labelling for H&S reasons
Widely used due to antibody specificity, sensitivity and that it is amenable to automation
Interference in immunoassay
Cross-linking antibody causing positive interference
Blocking antibody causing negative intereference
Usually a different test done if the test results do not match the patient
Clinical features of phaeochromocytomas
Excessive and episodic release of catecholamines may results in paroxysmal features: Hypertension Sweating, pallow Panic attacks Headaches Abdo pain Can also be asymptomatic
Testing for phaeochromocytomas
Using epinephrines due to the fact that it is more stable in the blood than catecholamines
Whipple’s Triad
Signs and symptoms of hypoglycaemia
Low plasma glucose
Resolution of symptoms once glucose level rises
Symptoms of hypoglycaemia
Hunger, sweating, anxiety parenthesis, palpitations, tremulousness, weakness, fatigue, dizziness, headache, confusion, behavioural changes, cognitive dysfunction, blurred vision, diplopia
Signs of hypoglycaemia
Pallor, tachycardia, widened pulse pressure, cortical blindness, hypothermia, seizures, coma
Common endogenous causes of hypoglycaemia
Insulinomas Insulin antibodies Critical organ failure Sepsis Hormone deficiency
Common exogenous causes of hypoglycaemia
Overuse of insulin
Drug interactions
Alcohol or other toxins
Insulinoma
Most common tumours from islets of Langerhans
Highest incidence 40-60 years
More females than males
Diagnosis of insulinoma
Fasting blood test
Low blood sugar (less than 2.2 mol/l)
High insulin (6 microunits/ml or higher)
High levels of C peptide (0.2 mol/l or higher)
Features of Cushing’s syndrome
Obesity - moon face, central obesity, shoulders Skin - thin, purple striae, bruising Hypertension Glucose intolerance Menstural disturbances/impotence Thin limbs/muscle weakness Back pain from osteoporosis Psychiatric disturbances - depression, psychoses
Difference between Cushing’s syndrome and disease
Cushing’s syndrome is any high cortisol condition
Cushing’s disease is specifically pituitary ACTH secreting tumour
Causes of Cushing’s syndrome
Pituitary ACTH secreting tumour (Cushing’s disease)
Cortisol producing tumour in the adrenal gland
Ectopic ACTH producing tumour
Iatrogenic
