Hypocalcaemia Investigation

Glasgow in the Sun

No more Part 1 revision - found out this week that I passed! Part 2 next sitting isn't until December so a chance to take to foot off the gas a bit for a couple of months before CMT starts up.

It's June, the sun is shining and summer is here. Lots of good things going on right now. Finalising my poster presentation at the moment for the British Association of Dermatologists' annual meeting in Liverpool and putting together an audit presentation for the West of Scotland Dermatology regional audit meeting later this month

Investigating Hypocalcaemia: This topic of discussion occurs in an educational article in this week's BMJ and covers an area which often causes me confusion as calcium metabolism is a complex process. It is not uncommon for a patient admitted acutely to hospital to be calcium depleted and a 'bone profile' investigation is a useful blood investigation to carry out on any unwell acute medical admission. Adjusted calcium levels (that is, serum albumin adjusted calcium concentrations) are the most informative. Common causes of hypocalcaemia include drug related causes, chronic kidney disease and post-operative hypoparathyroidism. In a patient with a low serum adjusted calcium level, a serum parathyroid hormone level is informative. Low serum calcium frequently occurs alongside low phosphate and magnesium levels and these should be checked. A cause of hypocalcaemia which seems to be coming increasingly frequent is due to inadequate sunlight exposure leading to lack of vitamin D. Vitamin D levels can be checked in patients believed to be at risk, although Vitamin D deficiency would not cause acute hypocalcaemia. 

Here is an example of how the serum phosphate and PTH levels can help in investigating the cause of hypocalcaemia:

Low phosphate + High PTH: ?Acute pancreatitis or drug induced eg. secondary to bisphosphonates

High phosphate + Low PTH: ?Hypomagnesaemia, hypoparathyroidism

High phosphate + High PTH: ?CKD or rhabdomyolysis

Patients with severe hypocalcaemia may become symptomatic with neuromuscular irritability and paraesthesia (think Chovstek & Trousseau's signs!). There may also be prolonging of the QT interval and therefore an ECG is indicated. Treatment may involve oral calcium supplementation if hypocalcaemia is mild, or IV calcium gluconate in the treatment of severe hypocalcaemia.