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53 Cards in this Set

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What does 1,25-dihydroxyvitamin D do?
increases absorption of calcium from the intestine and mobilizes calcium and phosphorus from bone
What is the current RDA of vitamin D?
200 IU/d
How much vitamin D is in 1L of infant formula?
400 IU vitamin D
What are the 3 type of rickets caused by vitamin D abnormalities?
Vitamin D Deficiency rickets, Vitamin D-resistant rickets, Vitamin D-dependent rickets
What does PTH do?
PTH increases the activity of enzyme 25-hydroxyvitamin D 1-alpha-hydroxylase
clinical presentation of vitamin D deficiency rickets: skeletal findings
craniotabes, enlargement of the costochondral junctions, scoliosis and kyphosis, enlargement at the wrists and ankles, coxa vara, and weak muscle tone; frontal bossing and rachitic rosaries (knobs along the anterior costochondral ridge)
clinical presentation of vitamin D deficiency rickets: non skeletal findings
Respiratory infections and pulmonary atelectasis that are related to severe chest deformities frequently are associated with rickets; convulsions, developmental delay, multiple fractures, decreased linear growth and bowing of the legs, short stature and poor weight gain
Vit D2
Ergocalciferol
Vit D3
Cholecalciferol
Which form of vitamin D is used to fortify dairy products?
Ergocalciferol (Vit D2)
How does cholecalciferol (vit D3) become vitamin D?
UV radiation causes cholecalciferol in skin to become vitamin D
Which position is hydroxylated first in Vitamin D?
25, then 1
Where is Vitamin D hydroxylated first?
in liver
Where does 25-hydroxyvitamin D become hydroxylated into 1,25-dihydroxyvitamin D?
in the kidney
What happens to PTH when 25-hydroxyvitamin D decreases?
As 25-hydroxyvitamin D levels decrease, parathyroid hormone (PTH) levels increase
At what point in the disease do rachitic changes become florid?
eventually both serum calcium and phosphorus concentrations decline as mineral absorption becomes inadequate to support normal serum calcium despite elevated PTH concentrations
What happens to PTH and phosphorus when serum calcium falls?
As serum calcium levels decrease, PTH increases. PTH restores calcium level in serum but leads to phosphaturia and decreased serum phosphate
How do you screen for vitamin D deficiency?
alkaline phosphatase and hemoglobin (level of 25-OH vitamin D is most sensitive but expensive)
Work up for suspected vitamin D deficiency rickets
Serum calcium, phosphorus, PTH, alkaline phosphatase, renal function tests, hydroxyvitamin D and dihydroxyvitamin D levels
+/- radiographs of long bones (ulna, radius, femur)
What causes congenital rickets?
low maternal intake of vitamin D and calcium
How do infants with congenital rickets present?
Affected newborns have very low calcium levels and may present with seizures or tetany in early infancy
Osteogenesis imperfecta is caused by what?
a defect in type II collagen which results in the formation of brittle bones that are fractured easily
How is diagnosis of OI made?
fibroblast biopsy
What is renal osteodystrophy?
Renal calcium loss causes increased PTH and may result in renal osteodystrophy
How does Renal tubular acidosis lead to bone disease?
hypophosphatemia and phosphaturia
What is Hyperphosphatasia?
excessively elevated serum levels of the bone isozyme of alkaline phosphatase.
How does hyperphosphatasia present?
Significant growth failure, bowing and thickening of the diaphysis and osteopenia
How does Primary chondrodystrophy present?
bowing of the legs, short stature, and a waddling gait in the absence of abnormalities in serum calcium, phosphorus, alkaline phosphatase, or vitamin D
What are the most sensitive/specific tests for vitamin D deficiency?
assays for 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D may be most sensitive and specific in diagnosing vitamin D deficiency
hypophosphatemic rickets
vitamin D-resistant rickets
What causes vitamin-D resistant rickets?
Defect in tubular reabsorption of phosphate
What causes Vitamin D-dependent rickets?
Reduced activity of 25(OH) 1-alpha-hydroxylase
What are the levels of 25-OH vitamin D in Vitamin D deficiency?
decreased
What are the levels of 25-OH vitamin D in Vitamin D resistant rickets?
normal
What are the levels of 25-OH vitamin D in Vitamin D dependent rickets?
normal
What are the levels of 1,25 (OH)2 vitamin D in Vitamin D deficiency?
Normal or increased
What are the levels of 1,25 (OH)2 vitamin D in Vitamin D resistant rickets?
Normal or decreased
What are the levels of 1,25 (OH)2 vitamin D in Vitamin D dependent rickets?
decreased
Treatment of vitamin D deficiency rickets:
supplemental calcium and initiate vitamin D therapy after diagnosis of vitamin D deficiency is confirmed
How much calcium?
1,000 mg supplemental calcium daily; also, increased dietary calcium
How much Vitamin D?
800 to 1,000 IU/d
How much calcium in 1 cup of milk?
300 mg
How much calcium in calcium fortified OJ?
160 mg
How much calcium in 1 cup yogurt?
300 mg
What is the level of calcium in Vitamin D deficiency rickets?
Decreased
What is the level of calcium in Vitamin D-resistant rickets?
Normal
What is the level of calcium in Vitamin D-dependent rickets?
Normal or decreased
What is the level of phosphorus in Vitamin D deficiency rickets?
Decreased
What is the level of phosphorus in Vitamin D-resistant rickets?
Decreased
What is the level of phosphorus in Vitamin D-dependent rickets?
Decreased
What is the level of PTH in Vitamin D deficiency rickets?
Increased
What is the level of PTH in Vitamin D-resistant rickets?
Normal or Increased
What is the level of PTH in Vitamin D-dependent rickets?
Normal or Increased