Treatment of Hypocalcaemia

Treatment of Hypocalcaemia

Calcium in serum is bound to proteins, principally albumin. As a result, total serum calcium concentrations in patients with low or high serum albumin levels may not accurately reflect the physiologically important ionized (or free) calcium concentration. As a result, ionized calcium remains the gold standard for assessing calcium status, particularly if the diagnosis of hypocalcemia is in doubt, due to hypoalbuminemia, atypical or absent symptoms, or a minimally reduced serum calcium concentration.¹

If a laboratory known to measure ionized calcium reliably is not available, the total calcium should be corrected for any abnormalities in serum albumin, using a calcium correction formula.¹

Calcium correction formula commonly used:

Corrected Serum Ca (in mmol/L) =

Measured Serum Ca (in mmol/L) + 0.8 – 0.02 x (Measured Albumin in g/L)

Bolus^1,2

Dilute 1-2 vials (10-20 mL) Calcium Gluconate 10% in (qs to) 50 mL NS or D5, infused over 10-20 mins (prefer 20 mins).

·      The calcium should not be given more rapidly, because of the risk of serious cardiac dysfunction, including systolic arrest

·      This dose of calcium gluconate will raise the serum calcium concentration for only two or three hours; as a result, it should be followed by a slow infusion of calcium in patients with persistent hypocalcemia.

IVI Calcium Gluconate^1,2

Dilute 5 vials (50 mL) Calcium Gluconate 10% in (qs to) 500 mL with NS or D5 to produce ~ 1 mg/mL elemental Ca solution¹

Start infusion with 50 mL/hr

The dose can be adjusted to maintain the serum calcium concentration at the lower end of the normal range, i.e. 2-2.25 mmol/L, with run rate of 0.5-2 mg/kg/hr (0.5-2 mL/kg/hr)²

·         Hypomagnesaemia must be corrected if present

·         Cardiac monitoring is indicated during Ca infusion. Stop Ca infusion if bradycardia ensues.

·         The IV solution should not contain bicarbonate or phosphate, which can form insoluble calcium salts. If these anions are needed, another IV line (in another limb) should be used.

·         Ca infusion should be given through a central line.³

Long Term Management²

1.    Oral Calcium Supplements:

·         Typical dosage is 800-2000 mg elemental calcium / day in divided doses

·         Calcium carbonate – should be taken WITH FOOD as the acidic environment in the stomach helps absorption.

·         Calcium citrate can be taken with or without food, and is useful in patients on proton pump inhibitors or conditions causing achlorhydria.

·         Elemental Ca content:

o   Calcium Lactate = 13% ; 1 tab of 300 mg = 39 mg

o   Calcium Carbonate = 40% ; 1 tab of 500 mg = 200 mg

o   Calcium Citrate = 20% ; 1 tab of 1 g = 200 mg

 

2.    Vitamin D:

·         In addition to calcium, patients with vitamin D deficiency or hypoparathyroidism require vitamin D supplementation, which often permits a lower dose of calcium supplementation.¹

·         Should be started as soon as oral calcium is begun.

·         If patient has severe hypophosphataemia, serum phosphorus should be lowered to < 2.1 mmol/L with oral phosphate binders before Vitamin D is started.

	Vitamin D Receptor Analogues (VDRA)
	Calcitriol	Alfacalcidol
Form	Active natural form of Vtamin D	Requires hepatic 25-hydroxylation to become active
Maintenance Dose	Usually initially 0.25 mcg OD, the usual maintenance dose is 0.5-2 mcg daily (in 2 divided doses) 2   OR   0.005-0.05 mcg/kg 3 times per week (Total of 2-3 mcg/day maximum dose)3	The usual maintenance dose is 0.5-1 mcg daily 2   OR   0.005-0.05 mcg/kg 3 times per week (Total of 2-3 mcg/day maximum dose)3
Time to Onset of Action	1-2 days	1-2 days
Time to Offset of Action	2-3 days	5-7 days (more prolonged)
Remarks		ü Similar efficacy as calcitriol, provided liver function is normal3 ü Longer offset time – to be considered e.g. when weaning patients off alfacalcidol post neck surgery.

 

3.    Phosphate binder (for hyperphosphataemia):

·      Usual Tab Calcium Carbonate dose range as phosphate binder is 1.5-2 g/day (elemental Ca).

·      May consider non-calcium based phosphate binder if Ca level is high.

Remarks:

For dialysis patient, may consider dialysate of higher Ca content if persistent hypocalcaemia.

References

1.       UptoDate: Treatment of hypocalcemia [Accessed 7 Dec 2020]

2.       Sarawak Handbook of Medical Emergencies (4^th Edition, 2019)

3.       Malaysian CKD-MBD and parathyroidectomy Guidelines and SOP (July 2018)