What tests should be done when a patient has a lab finding of hypernatraemia?
- Repeat U&Es
- Blood glucose
- Urine and simultaneous serum osmolality
What are the main differential diagnoses of hypernatraemia?
- Hypertonic plasma
- Diabetes insipidus with hypovolaemia
- Primary aldosteronism
Does hypernatraemia due to hypertonic plasma occur with hypervolaemia or hypovolaemia?
Can be either
Give an example of when hypernatraemia due to hypertonic plasma with hypervolaemia may occur?
Excess IV saline
Give an example of when hypernatraemia caused by hypertonic plasma with hypovolaemia may occur?
Diabetic polyuria, or diabetes insipidus
What suggests hypertonic plasma as the cause of hypernatraemia?
- Little hypotonic fluid orally or intravenously
- Thirsty
- High volume of urine with low sodium content
How is it confirmed that hypertonic plasma is the cause of hypernatraemia?
High plasma and urine osmolality
How is hypernatraemia caused by hypertonic plasma managed?
- Replace fluids, but avoid rapid changes. Give water orally, or IV in the form of 5% glucose
- Monitor serum electrolytes regularly
What suggests diabetes insipidus with hypovolaemia as the cause of hypernatraemia?
- Drinking excessively
- Passing large volume of urine
How is it confirmed that diabetes insipidus with hypovolaemia is the cause of hypernatraemia?
Increased plasma osmolality and decreased urine osmolality
How is hypernatraemia caused by diabetes insipidus with hypovolaemia managed?
- Replace fluid, avoid rapid changes. The aim is to reduce sodium at a rate of <10mmol/L per day
- Desmopressin 100-200mg tds orally IM
Give two causes of primary aldosteronism
- Adrenal hyperplasia
- Conn’s syndrome with adrenal tumour
What suggests primary aldosteronism as the cause of hypernatraemia?
- Normal fluid intake
- Increased BP
- Decreased serum potassium
- Metabolic alkalosis
How is it confirmed that primary aldosteronism is the cause of hypernatraemia?
- Decreased plasma renin activity
- Increased aldosterone levels
- CT or MRI scan
How is bilateral adrenal hyperplasia treated?
Spironolactone, amiloride, or eplerenone
How is an aldosterone-producing adenoma managed?
Adrenalectomy
