Calcium and Vitamin D Disorders Flashcards
(27 cards)
45% of serum calcium is bound to…
protein, primarily albumin. Albumin levels will alter serum calcium levels
If the pH were in a state of alkalosis what would happen to the binding of albumin?
increased binding to albumin
If the pH were in a state of Acidosis what would happen to the binding of albumin?
decreased binding to albumin
What is Calcium regulated by?
PTH, vit D via effects on bone , kidney and GI tract
Negative inhibition by acting on Ca Sensing receptor (CaSR)
At level of PTH gland-inhibits release of PTH
Kidney: inc excretion of calcium, dec calcium reabsorption
Primary hyperparathyroidism is most commonly cause by what?
85% single adenoma
Where does most of the loss of BMD in PHPTH occur?
lumbar spine
What are the guidelines for surgical management of Asymptomatic HPTH?
Plasma calcium >1.0 mg/dL of the ULN
Calculated Cr C <50 years
Monitoring:
Yearly serum Ca++
Yearly Plasma Cr
BMD every 1-2 years
Preoperative localization for PHTPH
Done once a diagnosis is made and pt to have surgery
Sestamibi scan
US neck
CT neck
What are the treatment guidelines for hypercalcemia?
Ca< 12-14 mg/dL: may be tolerated chronically and may not require immediate therapy
Calcium >14 mg/dL requires therapy, regardless of symptoms
How do we treat hypercalcemia?
IV hydration:
Saline 200-300 ml/hr
Adjust to keep urine output 100-150mL/h
Diuresis with lasix only if signs of fluid overload
Calcitonin/Bisphosphonates
Use of Calcimimetics (inhibit PTH release)
Dialysis in some cases
Glucocorticoids when indicated
Identify/Treat underlying cause
Calcitonin
Osteoclast inhibitor/inc renal excretion
4IU/kg, IV or SC, Q12 hours
can be increased to 6-8 IU/kg Q6 hr
Nasal form not efficacious
Rapid reduction in calcium (within 4-6 hours)
Short lived effect-limited to initial 48 hrs
tachyphylaxis (poss receptor down-regulation)
Bisphosphonates
Pamidronate
Zolendronate
Osteoclast inhibitors
IV route
Expect reduction in serum calcium 24-36 hours
Duration of effects is variable
Cinacalcet
Calcimimetic- inc the sensitivity of the CaSR to extracellular calcium
Inhibits PTH release
Indications:
parathyroid cancer
secondary HPTH
non surgical primary HPTH with severe hypercalcemia
Pseudohypoparathyroidism
Resistance to PTH action
2/2 to defective signaling of PTH action via cell membrane receptor (G- protein)
Elevated PTH level, elevated phosphorus and low calcium
Also affects TSH, LH, FSH, GH signaling
Autosomal Dominant gene mutation of GNAS1 ( alpha subunit of G protein):
G protein is unable to activate downstream signaling and end organ response to PTH
GNAS1 is imprinted in humans so what is expressed depends on how an allele was transmitted:
Maternal transmission (type 1 A):
-biochemical abnormalities + phenotypic features
paternal transmission (pseudo-pseudo): -phenotypic features only
Albright’s hereditary osteodystrophy
Most common type of pseudo-hypoparathyroidism (type 1 A)
Labs: Inc PTH, Inc phos and low Calcium and resistance to other G protein coupled hormones Constellation of symptoms: Short stature Obesity Round face Developmental delay Short metacarpals 4 and 5, dimples instead of knuckle
Clinical features of hypocalcemia
Neuromuscular irritability Paresthesias Chvosteks’ sign Trousseau’s sign Prolonged QT interval Broncho, carpal or laryngeal spasm Seizures
Management of hypocalcemia
Indications for acute treatment
Symptoms present
Asymptomatic with:
Serum calcium <7.5 mg/dL
Hx of seizure
Abnormal EKG
Emergency management of hypocalcemia
IV calcium gluconate ( less likely to cause tissue necrosis)
Cardiac monitoring
For immediate relief of symptoms:
-20 ml of 10% calcium gluconate diluted in 100-200 ml of NS or D5 infused over 10 min
- (10 ml=2.25mmol elemental calcium)
-transient effect, lasting 2-3 hrs
- need slow gtt to follow (40 ml of 10% calcium gluc in 1 L saline or D5 over 24 hrs )
Management of chronic hypocalcemia
Manage underlying etiology
Oral calcium
- 1.0-1.5 g elemental calcium/day - 1 gram oral calcium, (calcium carbonate) = 400 mg of elemental calcium
Oral vitamin D
-calcitriol preferred 0.25-0.5 mcg 1- 2x/day
Manage underlying etiology
Goal of therapy: calcium at or below the normal limit
Higher levels result in hypercalciuria
Oral calcium
- 1.0-1.5 g elemental calcium/day - 1 gram oral calcium, (calcium carbonate) = 400 mg of elemental calcium
Oral vitamin D
-calcitriol preferred 0.25-0.5 mcg 1-2x/day
Osteomalacia risks
Results from inadequate mineralization of bone
Decreased bone strength and increased risk for fracture
Osteomalacia- adult bone
Impaired mineralization of the bone matrix
Rickets – occurs in children at the epiphysis of the growing skeleton
Un-mineralized osteoid at the growth plate
?
Rickets and osteomalcia occur together when growth plates are open
Only osteomalcia occurs after growth plate has closed
Results from inadequate calcium, phosphate or vitamin D
Clinical features of osteomalacia
Bone pain Deformity Fracture Proximal myopathy Hypocalcemia (vit D def)
clinical features of rickets
Growth retardation Bone pain, fractures in unusual locals (scapula, pubic rami) Skeletal deformity Bowing of long bones Widening of the growth plates
Vitamin D deficiency
Decreased skin production Elderly, housebound Pigmented skin sunscreen Obese Poor nutrition Malabsorption
Secondary hyperparathyroidism
Malabsorption
Gastric bypass
Drugs –phenytoin (inc metab of vit D)
