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E40 Endocrinology
Calcium Homeostasis
Toronto Notes 2019
Acute Management of Hypercalcemia/ Hypercalcemic Crisis
• Volume expansion (e.g. NS IV 300-500
cc/h): initial therapy
• Calcitonin: transient, partial response
• Bisphosphonate: treatment of choice
• Corticosteroid: most useful in vitamin D
toxicity, granulomatous disease, some
malignancies
• Saline diuresis + loop diuretic (for volume
overload): temporary measure
Differential Diagnosis of Tetany
• Hypocalcemia
• Metabolic alkalosis (with hyperventilation) • Hypokalemia
• Hypomagnesemia
Approach to Hypocalcemia
1. Is the patient hypocalcemic?
2. Is the PTH high or low?
3. If PTH is high, is phosphate low or normal? 4. Is the Mg2+ level low?
Approach to Treatment
• correctunderlyingdisorder
• treatconcurrenthypomagnesemia
• mild and symptomatic (ionized Ca2+ >0.8 mmol/L)
■ calcium supplementation - 1500-2000mg of elemental calcium per day
■ calcitriol 0.25 μg/d (especially in renal failure or hypoparathyroidism) • note:thisdoseistypicallyhigherinhypoparathyroidism
• acute or symptomatic hypocalcemia (ionized Ca2+ <0.7 mmol/L)
■ immediate treatment required
■ IVcalciumgluconate1-2gover10-20minfollowedbyslowinfusion
■ if underlying cause is hypoparathyroidism, the goal is to raise Ca2+ to low normal range (2.0-2.1
mmol/L) to prevent symptoms but allow maximum stimulation of PTH secretion • ifPTHrecoverynotexpected,requireslong-termtherapywithcalcitriolandcalcium • startoralcalciumandcalcitriolconcurrentlywithIVcalciuminfusion
• donotcorrecthypocalcemiaifasymptomaticandsuspectedtobetransient
Low Ca2+
Initial investigations: PTH, PO43-, Mg2+, Urine Ca2+, creatinine
􏰀PTH Normal PO43-
Pseudohypoparathyroidism:
PTH resistance secondary to G-protein deficiency
Acute Pancreatitis: Release of pancreatic caldecrin decreases bone resorption
Drugs: Calcitonin, loop diuretics 􏰁 Calcidiol
(25-OH Vit D)
􏰁 Intake and/or Malabsorption: e.g. celiac disease, IBD, gastric bypass, CF
Nephrotic Syndrome:
Lose Vit D binding protein
Drugs: Phenobarbital, phenytoin, carbamazepine, rifampin, isoniazid
􏰁PO43- Vit D related
􏰁 Calcitriol (1,25-(OH)2 Vit D)
Chronic Renal Failure
Vit D Dependent Rickets Type I: Renal 1-α-hydroxylase deficiency
Low Mg2+
Normal or􏰁PTH Liver
Dysfunction Hemochromatosis
Parathyroid Gland Destruction
Drugs:
Antineoplastic agents
􏰀 Calcitriol (1,25-(OH)2 Vit D)
Alcoholism
Iatrogenic Hypoparathyroidism: Post-thyroidectomy 131I ablation Post-surgical correction of primary hyperparathyroidism
Primary Hypoparathyroidism: Idiopathic/autoimmune hypoparathyroidism Infiltrative disease of parathyroid gland HIV
Figure 18. Etiology and clinical approach to hypocalcemia
Transient hypoparathyroidism (resulting in hypocalcemia) common after subtotal thyroidectomy (permanent in <3% of surgeries)
Online Clinical Tools
CAROC www.osteoporosis.ca/multimedia/pdf/ CAROC.pdf
FRAX
www.shef.ac.uk/FRAX/tool.aspx
Hereditary Vit D Resistant Rickets Type II: Receptor defect
Secondary Hyperparathyroidism: Appropriate PT gland response to low serum Ca2+