Calcium and Phosphate Disorders (Rahhal)

Question 1

What are the 2 main effects of vitamin D?

Answer 1

enhances calcium and phosphorus absorption from the gut and mobilizes calcium stores from the bones

Question 2

What are the main functions of parathyroid hormone?

Answer 2

1. mobilizes Ca and P from bone by activating osteoclasts
2. promotes Ca reabsorption and P excretion by the kidneys
3. activates Vit D

Question 3

primary hyperparathyroidism is characterized by (high or low) Ca2+ and (high or low) PTH.

Answer 3

high; high

Question 4

Which of the following regarding calcium homeostasis is FALSE?
A. 99% of total body calcium is stored in the bone
B. Most of the 1% extracelluar calcium is ionized and biologically active
C. Acidosis leads to a decrease in the amount of bound calcium and an increase in the free fraction
D. Alkalosis increases calcium binding and decreases the ionized fraction
E. Most bound extracellular calcium is bound to albumin

Answer 4

B. Most of the extracellular calcium (~55%) is in the bound form.

Question 5

Which of the following statements regarding PTH is FALSE?
A. PTH production is regulated by ionized calcium through the calcium sensing receptor CaSR
B. PTH Binds to the PTH receptor in the kidneys and bone
C. The main defense against hypercalcemia is PTH suppression
D. All forms of hereditary hyperparathyroidism are autosomal dominant
E. Hypercalcemia in the presence of a normal PTH suggests secondary hyperparathyroidism

Answer 5

E. High calcium with a normal PTH still points toward relative overproduction of PTH and suggests primary hyperparathyroidism. A normal PTH in face of hypercalcemia is ABNORMAL (the PTH should be low when the calcium is high if the parathyroid glands are functioning properly).

Question 6

this risk of hyperparathyroidism is caused by deposition of calcium in the kidney, leading to decreased kidney function

Answer 6

nephrocalcinosis

Question 7

how does hyperparathyroidism cause kidney stones, when overactive parathyroid leads to reabsorption of calcium from the urine?

Answer 7

Although PTH itself increases tubular calcium reabsorption, the high serum calcium can overcome the reabsorption threshold and lead to hypercalciuria

Question 8

what are the 3 risks of hyperparathyroidism?

Answer 8

nephrocalcinosis, kidney stones, and osteoporosis

Question 9

What treatment is recommended for a person who has very high serum calcium but does not want surgery?

Answer 9

treat with the drug cinacalcet, which is a calcimimetic that feeds back to the parathyroid, leading to a decreased secretion of PTH

Question 10

what treatment is recommended for a person who has osteoporosis but does not want surgery?

Answer 10

if serum Ca+ is not too high, can treat with bisphosphonate - decreases bone resorption

Question 11

this condition is easily confused with primary hyperparathyroidism, and is caused by an autosomal dominant inactivating mutation in the gene for the calcium-sensing receptor CaSR

Answer 11

FHH: familial hypocalciuric hypocalcemia

Question 12

How is FHH (familial hypocalciuric hypocalcemia) distinguished from primary hyperparathyroidism?

Answer 12

in FHH, urine concentration of calcium is very low, whereas in primary hyperPT it is high

Question 13

Which of the following regarding hypercalcemia of malignancy is FALSE?
A. Hypercalcemia of malignancy is the most common cause of hypercalcemia in hospitalized patients
B. Hypercalcemia of malignancy is characterized by a high serum calcium level and a high PTH
C. Lung and renal cell malignancies produce a parathyroid hormone related protein called PTHrP
D. Lymphoma, myeloma and leukemia produce osteoclast activating factors as well as 1,25(OH)2 vit D

Answer 13

B. With hypercalcemia of malignancy, serum calcium is high and PTH is low in an attempt to correct the problem.

Question 14

Vitamin A/D toxicity, immobilization, and milk alkali syndrome are all forms of PTH-_____ hyperparathyroidism and are characterized by (high or low) PTH

Answer 14

independent; low

Question 15

what acute therapy is used to correct serum hypercalcemia?

Answer 15

induce natruiresis - give saline, and this drives excretion of sodium (calcium follows) in the proximal tubules

Question 16

what are maintenance treatments for hypercalcemia more long term?

Answer 16

bisphosphontaes - reduce bone resorption

glucocorticoids - for granulomatous disease

Question 17

how do bisphosphonates work?

Answer 17

they attach to bone surfaces where they are internalized by osteoclasts - this impairs the osteoclasts ruffled borders, impairs their adherence to the bone, and impairs their H+ production. It also decreases osteoclast differentiation and increases apoptosis

Question 18

carpopedal spasm and chostek’s sign are associated with (hypo or hyper) calcemia?

Answer 18

hypocalcemia

Question 19

in hypoparathyroidism, would the following lab values be increased or decrease?
Ca:____
PO4:_____
PTH:_____

Answer 19

Ca: low
PO4: high
PTH: low

remember that parathyroid hormone makes you dump PO4 in the urine. so if you don’t have PTH, your PO4 concentration will be elevated in the serum.

Question 20

in vitamin D deficiency, would the following lab values be increased or decrease?
Ca:____
PO4:_____
PTH:_____

Answer 20

Ca: low
PO4: low
PTH: high

Question 21

Predict the following lab values for pseudohypoparathyroidism (resistance to PTH):

Calcium:____
Phosphorus:_____
PTH:____
1,25 (OH)2 vitamin D:____

Answer 21

Calcium: low
Phosphorus: high
PTH: high
1,25 (OH)2 vitamin D: low

Question 22

Predict the following lab values for vitamin D resistant rickets:

Calcium:____
Phosphorus:_____
PTH:____
1,25 (OH)2 vitamin D:____

Answer 22

Calcium: low
Phosphorus: low
PTH: high
1,25 (OH)2 vitamin D: high

Question 23

What is the treatment for hypocalcemia?

Answer 23

it depends on the reason:

If patient has vitamin D deficiency, they just need plain old, inactive over the counter vitamin D supplements to help them absorb the calcium.

If patient has hypoparathyroidism, they don’t make PTH and can’t convert inactive vitamin D –> active, so they need the activated form of vitamin D.

Question 24

OP is a 57 year old woman who returns for her yearly check-up. She has been feeling well except for some fatigue that she attributes to her busy schedule. Her physical examination is normal and routine blood tests show normal kidney function, normal electrolytes, a normal fasting glucose and a normal CBC. You notice an elevated serum calcium of 11.2 mg/dl (normal is 8.5-10.5) with a normal albumin. In trying to diagnose the cause of her hypercalcemia, what test should be done next?

A. 25 hydroxyvitamin D
B. 1,25 dihydroxyvitamin D
C. Parathyroid hormone (PTH)
D. Parathyroid hormone-related (PTH-rp)
E. Anionized calcium since the total calcium is falsely elevated

Answer 24

C.