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9 Cards in this Set
- Front
- Back
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PTH
-physiologic function and location of action (3) -overall affect |
1. Acts on the kidneys to increase calcium reabsorption and inhibig phosphate reabsorption
2. Activates 1-alpha hydroxylase, which converts hydroxyvitamin D to calcitriol - promoting increase in serum calcium 3. Acts in the bone to promote osteoclast activity - increase in serum calcium Net effect: Increase in serum calcium and decrease in serum phosphate |
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How do you correctly measure serum calcium?
-two methods |
1. Measue the ionized calcium, but this poorly done in most labs and it must be done immediately and anaerobically
2. Measure the total calcium with serum albumin or total serum protein and adjust for the bound calcium: Measured Ca + 0.8 x (4.2 - albumin) Measured Ca + 0.5 x (7.2 - total protein) |
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What is the best test to measure vitamin D deficiency?
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Measure the 25(OH)D3 level - this is the storage form of vit D
Measuring 1,25(OH) D3 (calcitrol) is useless because it is always maintained in a narrow range regardless of Vit D stores |
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Hypercalcemia
-common symptoms (5) |
1. Fatiuge, subjective muscle weakness, musculoskeletal aches and pains
2. Depression 3. Increased thirst and polyuria 4. Consipation 5. No symptoms (most common) |
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Hypercalcemia
-high PTH level (3) |
1. Primary hyperparathyroidism
2. Renal failure leading to tertiary hyperparathyroidism 3. Familial hypocalciuric hypercalcemia - very rare, higher intrinsic set point for calcium modulation |
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Hypercalcemia
-Low PTH level (5) |
1. PTHrP mediated malignancy - most common
2. Bone destruction by metastases and hematologic malingnancies 3. High bone turnover 4. Excessive calcium absorption from the gut - Vit D intoxication 5. Excessive calcium intake |
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Hypocalcemia
-differential diagnosis with associated PTH level for the condition -which is the most common |
1. Vit D deficiency from nutritional deficiency or lack of sunlight - high PTH
2. Hypoparathyroidism - idiopathic, autoimmune, surgical or genetic - low PTH 3. Malabsorption syndrome - high PTH 4. Psuedohypoparathyroidism (PTH resistance) - high PTH 5. Chronic renal failure - loss of 1-alpha-hydroxylase - high PTH - most common |
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Hypocalcemia
-symptoms -clinical signs |
Symptoms depend on severity and rate of fall in serum calcium - paresthesia, tetany
Positive Chvostek's (lip twitch) and Truosseau's (BP cuff) sign |
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FGF23
-physiological effects -consequences of elevation |
-secreted by osteocytes, regulated by phosphate levels
-inhibits renal phosphate reabsorption and supresses 1-alpha-hydroxylase production (decreases vit D production) - excess causes hypophosphatemia with normal calcium and PTH, but low vit D -can lead to tumor-induced osteomalacia |
