Electrolyes -- Calcium
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þ Calcium Metabolism
 - fractional excretion of Ca++ liess than 1%
 - about 50% of calcium is bound to plasma proteins
 - 1.0 mmol = 4 mg% (4 mg/dL)
 - PTH causes:
  + increased Ca++ and PO4-- via effects on bone and intestine
  + increased Ca++ and DEcreased PO4-- via effects on kidney
  + increased 1,25 DHCC (vitamin D) in the kidney, that then causes increased
    absorption in the gut.
 - Calcitonin (after a large calcium load in the gut) causes
  + decreased Ca++ and PO4-- via effects on bone.
 - Vitamin D causes:
  + increased Ca++ and PO4-- via effects on both intestine and bone
  + vitamin D metabolism:
   - cholesterol absorbed in gut
   - in skin, changed to the 7-dehydro form
   - in liver, converted to 25-dehydro form
   - in kidney, converted to the most active 1,25 dehydrocholecalciferol
     (1,25 DHCC)

þ Calcium Levels
 - with normal albumin and globulin concentrations:
   Ionized calcium = Total calcium - (0.8 x Total protein).
   Protein is in g/dL and calcium is in mg/dL
 - with abnormal albumin and globulin concentrations:
   Ionized calcium = Total calcium - (1.1 x albumin) - (0.2 x
   globulin) where albumin is in g/dL and calcium is in mg/dL.
   --Tintinalli, 3rd ed. p74

þ Hypocalcemia
 - Cimetidine lowers serum calcium levels, either by decreasing the synthesis
   or the secretion of parathyroid hormone. Therefore, it should not be used
   in patients with hypocalcemia.
   Reference:  Tintinalli 3rd ed. p 75
 - Hypocalcemia in rhabdomyolysis
   <Rhabdo.TXT -calcium>

þ Hypercalcemia
 - factitious hypercalcemia can be caused by a tourniquet on the arm for a
   long time for blood draws.