PTH/Minerals/Vitamin D

Question 1

What electrolyte abnormalities do you see with primary hyperparathyroidism?

Answer 1

hypercalcemia
hypophosphatemia maybe (only seen in 50%

Question 2

What is the most common cause of primary hyperthyroidism?

Answer 2

benign parthyroid neoplasm or adenoma

Question 3

What are the other two main causes of primary hyperparathyroidism?

Answer 3

parathyroid hyperplasia

parathyroid carcinoma

Question 4

Patients with primary hyperparathyroidism are usually asymptomatic, but if they do have symptoms what would you expect?

Answer 4

bones, stones, groans, psychiatric overtones

Question 5

After diagnosing primary hyperparathyroidism, would you order any other lab tests?

Answer 5

urine calcium (24 hr is better than random)

Question 6

If you find that the 24 hr urine calcium is low, what is the diagnosis?

Answer 6

familial hypocalcuric hypercalcemia

Question 7

What are the three different forms of calcium in blood?

Answer 7

protein-bound (40-45%)

free (ionized) (45-50%)

complexed (PO4, HCO3, Lactate), 5-10%

Question 8

How does pH affect the free calcium levels?

Answer 8

Alkalemia DECREASES free calcium (more bound to albumin)

Acidemia INCREASES free Ca

so Ca binding is directly correlated to pH; lower pH = less binding = more free Ca

for each 0.1 change in pH, free Ca changes by 5%

Question 9

What is the main purpose of free ionized calcium?

Answer 9

maintenance of hemodynamic function: cardiac contractility, vasoactive tone, etc.

Question 10

Why do you need to correct the total calcium to account for protein?

Answer 10

Because higher protein levels will lead to more calcium bound and increase the total calcium even though that bound calcium isnt doing anything and we don’t care about it.

Question 11

What is the equation for the corrected total calcium?

Answer 11

measured total Ca + 0.8*[4-Albumin]

Question 12

What do we need to correct the free ionized calcium level for?

Answer 12

pH level

Question 13

What is the iCa pH correction formula?

Answer 13

Measured iCa[1-0.53(7.4-measured pH)]

Question 14

When do we test the ionized calcium?

Answer 14

Really only used as a reflex test if the total calcium is less than 8 or more than 10.2

Question 15

What are the three circulating forms of PTH?

Answer 15

First, PTH starts as a peptide with an N and C terminal, which are variable cleaved.

So:

1. Intact, bioactive OTH
2. N-truncated PTH
3. C-terminal fragments

Question 16

Parathyroidectomies may be guided by serum PTH concentrations. A decrease in PTH of what in 10 minutes post-resection signals success in removing the abnormally secreting parathyroid tissue.

Answer 16

over 50%

Question 17

What are some renal causes of hypomagnesemia?

Answer 17

meds (diuretics, cisplatin, aminoglycosides, cyclosporin)

infection (pyelo, glomerulo)

Osmotic diuresis

Question 18

What are some GI causes of hypomagnesemia?

Answer 18

diarrhea, vomiting
laxative abuse
lack of intake/absorption
malabsorption
malnutrition
alcoholism
TPN

Question 19

How does hypomagnesemia lead to secondary hypoparathyroidism?

Answer 19

…

Question 20

How do you exclude renal loss of Mg?

Answer 20

check urine Mg

Question 21

How long does someone need to be on PPIs before they develop hypomagnesemia?

Answer 21

median # of years before onset is 5.5

Question 22

In an infant with elevated PTH and normal calcium, what lab should you check?

Answer 22

vitamin D level!

Question 23

What vitamin D level should you test to get the most accurate idea of a patient’s true vit D status?

Answer 23

25-OH

Question 24

Can your body still form vitamin D if you wear sunscreen?

Answer 24

Not nearly as much. Whole body SPF 8 reduces the capacity to produce Vit D3 by 95%

Question 25

What biochemical changes do you see in late stage Vit D deficiency?

Answer 25

Low calcium
low phos
way low urinary Ca
increased PTH

Question 26

What is the disease state with vit D def in kids?

Answer 26

Rickets

Question 27

What are the signs of rickets?

Answer 27

skeletal deformities (delayed fontanelle closure, bowed legs, breastbone projection)

weakness
unable to stand/walk
slow growth
bone pain/tenderness
seizures (hypocalcemia)
dental deformities

Question 28

Vitamin D def is associated with what other deficiency?

Answer 28

iron

and interestingly, treatment with iron can increase vitamin D levels!

Question 29

What group of patients definitely need Vit D supplementation without question?

Answer 29

breastfed infants