Abnormal Blood Tests Flashcards
Define hyponatraemia.
- Normal range of sodium in serum 135-145 mmol/L
- Hyponatraemia = Na < 135 mmol/L
- Mild = 130-135 mmol/L
- Moderate = 125-129 mmol/L
- Severe <124 mmol/L
- Acute < 48 hours
- Chronic > 48 hours
What are the clinical features of hyponatraemia?
- Can be an incidental finding with no symptoms.
- Symptoms correlate with severity of hyponatraemia but also due to the speed at which hyponatraemia develops.
- When plasma osmolality falls quickly, water rapidly flows into cerebral cells causing swelling.
- Gradual development allows cerebral cells to reduce intracellular osmolality, so the osmotic gradient forcing is reduced.
What are the causes of hyponatraemia?
Describe the pathophysiology of these causes.
What is SIADH?
- ADH works to promote water retention in the distal tubule.
- Released in response to increasing plasma osmolality.
- In SIADH, ADH causes excessive water retention without a physiological cause, resulting in hyponatraemia.
Describe the management of hyponatraemia.
- Treatment depends on severity, acuity and underlying cause.
- Acute onset with signs of cerebral oedema - prompt correction with hypertonic saline.
- In chronic hyponatraemia, rapid overcorrection can be very dangerous, so slow correction is key (< 10mmol/L/24h).
- Correct hypovolaemia.
- Euvolaemic / hypervolaemic - fluid restriction.
Define hypernatraemia.
- Normal range of sodium in serum 135-145 mmol/L.
- Na >145 mmol/L = hypernatraemia.
- Severe hypernatraemia > 160mmol/L.
- Hypernatraemia represents a defecit of water relative to sodium.
Describe the pathophysiology of hypernatraemia.
Give examples of causes.
What are the appropriate investigations of a patient with hypernatraemia?
- Electrolyte, glucose, renal biochemistry.
- Urine osmolality / serum osmolality.
- Urine electrolytes.
- Desmopressin challenge tests.
- MRI or CT brain.
How is hypernatraemia managed?
- Depends on the cause.
- Oral fluids.
- IV fluids with caution.
- Treatment of Diabetes Insipidus.
Define hyperkalaemia.
- Potassium is the major intracellular cation.
- Crucial to normal functioning of nerves, muscles and the heart.
- Normal range of potassium in serum = 3.5-5.5 mmol/L.
- Hyperkalaemia = >5.5mmol/L.
- Mild = 5.5-5.9 mmol/L
- Moderate = 6.0-6.4 mmol/L
- Severe = >6.5 mmol/L
What are the clinical features of hyperkalaemia?
- Mild - moderate high K is asymptomatic.
- Severe high K can cause muscle weakness, but sometimes even severe hyperkalaemia can be relatively asymptomatic untill collapse / arrest.
Describe the investigation of hyperkalaemia?
- Blood tests
- Creatinine / eGFR
- Sodium
- Bicarbonate
- ECG
Describe the pathophysiology of hyperkalaemia.
Give examples of causes.
Describe the management of hyperkalaemia.
Emergency Management!
Define hypokalaemia.
- Normal range for potassium = 3.5-5.5 mmol/L.
- Hypokalaemia = <3.5 mmol/L.
What are the clinical features of hypokalaemia?
- Asymptomatic 3.0-3.3 mmol/L.
- Severe hypokalaemia causes:
- Muscle weakness
- Tiredness
- Paralytic ileus
Describe the pathophysiology of hypokalaemia.
Give examples of causes.
What are the investigations for hypokalaemia?
- Blood tests
- Bicarbonate
- Magnesium
- Calcium
- ?Renin
- Urinary potassium
Describe the management of hypokalaemia.
- Treat the underlying cause.
- Replacement
- KCl orally
- IV - higher concentrations should be given centrally
Define hypercalcaemia.
- Normal calcium level 2.1-2.6 mmol/L.
- Hypercalcaemia = > 2.6 mmol/L.
- Bound to albumin, so level needs to be corrected for hypoalbuminaemia.
- Adjusted calcium = Total calcium - 0.02 (40 - Albumin)
- Common biochemical abnormality.
What are the clinical features of hypercalcaemia?
- Can present acutely with severe hypercalcaemia and dehydration.
What are the causes of hypercalcaemia?
* Commonest cause of primary hyperparathyroidism is single adenoma.
Describe the appropriate investigation of hypercalcaemia.
- PTH is the key test
- Phosphate also helpful
- Renal function (tertiary hyperparatyroidism)
- Screen for malignancy - CXR, myeloma screen, CT imaging
Describe the management of hypercalcaemia.
- Treat the underlying cause.
- Urgent management.
Define hypocalcaemia.
- Normal range for calcium = 2.1-2.6 mmol/L.
- Hypocalcaemia = <2.1 mmol/L.
- Bound to albumin, so level needs to be corrected for hypoalbuminaemia.
- Less common than hypercalcaemia.
What are the clinical features of hypocalcaemia?
- Mild hypocalcaemia is usually asymptomatic.
- Severe hypocalcaemia - muscle spasm and tetany.
- Signs:
- Trousseau’s sign (‘main d’accoucheur)
- Chvostek’s sign
Describe the pathophysiology of hypocalcaemia?
Give examples of causes.
Describe the management of hypocalcaemia.
- Depends on the cause.
- Emergency management of severe hypocalcaemia = IV calcium gluconate.
Define hypomagnesaemia.
Serum magnesium <0.75 mmol/L.
What are the clinical features of hypomagnesaemia?
- Mild - asymptomatic.
- Severe - tetany.
Describe the pathophysiology of hypomagnesaemia.
Give examples of causes.
- Inadequate intake - EtOH excess, malnutrition.
- Excessive loss - urinary / GI.
- Other - PPI, pancreatitis.
What is the most important investigation in a patient with hypomagnesaemia?
ECG
Describe the management of hypomagnesaemia.
- Treat the underlying cause.
- IV magnesium. Oral Mg has limited use.
Define hypermagnesaemia.
Serum magnesium >1.0 mmol/L.
What are the clinical features of hypermagnesaemia?
- Bradycardia
- Hypotension
What is the main cause of hypermagnesaemia?
Magnesium-containing medications.
How do you manage hypermagnesaemia?
Promote renal excretion
Define hypophosphataemia.
Serum phosphate <0.8 mmol/L.
What are the causes of hypophosphataemia?
- Redistribution into cells - refeeding syndrome.
- Inadequate intake - malnutrition. phosphate binders.
- Increased excretion - primary hyperparathyroidism.
How should hypophosphataemia be managed?
- Oral supplementation.
- IV in critical care.
Define hyperphosphataemia.
Serum phosphate >1.4 mmol/L.
What are the clinical features of hyperphosphataemia?
- Pruritis
- Long term calcium phosphate deposition
What are the causes of hyperphosphataemia?
- AKI
- CKD
Describe the management of hyperphosphataemia.
- Dietary restriction
- Phosphate binding drugs
