Hypocalcemia Flashcards
1
Q
Causes of hypoCa
A
- Low serum albumin (most common)
- Chronic renal failure
- Mg deficiency
- Hypoparathyroidism
- Pseudohypopara (PHP)
- Osteomalacia due to vit D def
- Hungry bone syndrome
- Acute hemorrhagic pancreatitis
- Hyperphosphatemia
2
Q
HypoCa due to low albumin
A
- Can be from malnutrition, liver cirrhosis, nephrotic syndrome
- Always correct the Ca to albumin: TrueCa = MeasuredCa + (4-alb)x.8
- Thus if the albumin is low it will make the Ca look lower than it is (may not actually be hypoCa)
3
Q
HypoCa due to chronic renal failure
A
- Multifactorial: decreased 1,25OHD leads to inability to absorb Ca
- Hyperphosphatemia (inability to excrete PO4) can lower Ca
- There can be skeletal resistance to PTH
- The BUN and creatinine will be high
4
Q
Causes of Mg deficiency
A
- Mg deficiency arises when there is Mg loss either from GI tract or kidneys
- GI reasons for Mg def: low dietary intake, malabsorption (think pts after bariatric surgery, celiac disease), diarrhea, intestinal/biliary fistulas, acute hemorrhagic pancreatitis, primary intestinal Mg malabsorption (mutation in Mg channel), H+ pump inhibitors
- Renal causes: osmotic diuresis (diabetes), chronic IV fluids, ETOH, diuretics, metabolic acidosis, drugs (aminoglycosides, cisplatin, amphotericin), immunosuppression (cyclosporin)
5
Q
HypoCa due to Mg deficiency 1
A
- HypoCa secondary to Mg deficiency should be considered when there is hypoCa w/ inappropriately low or nl PTH (PTH should be high) and one of the conditions that causes Mg def is met
- Giving Mg to nl pts suppresses PTH release (binds to the CaSR), but giving Mg to Mg deficient pts increases PTH release
- This is b/c Mg is required both for PTH release and its action at its receptors
- PTH will only work when Mg levels are nl
- Thus if Mg is replenished in a pt that was Mg deficient and hypoCa, the Ca will return to normal levels after 3-4 days (PTH will correct in mins/hours)
6
Q
HypoCa due to Mg deficiency 2
A
- PTH receptor requires Mg for second messenger systems to be activated
- The CaSR requires Mg to function, and w/o Mg the receptor cannot sense the fall in Ca and the body won’t release PTH
- Mg deficiency causing hypoCa is multifactorial: impaired PTH secretion, renal and skeletal resistance to PTH, impaired formation of 1,25OHD, resistance to 1,25OHD
- These are all corrected when Mg is replenished
7
Q
HypoCa from hypopara
A
- 90% is post-surgical (parathyroids were removed), 10% is idiopathic (autoimmune)
- Other causes: congenital, infiltrative diseases, radiation Rx, activating mutations in CaSR (decreasing setpoint, increasing sensitivity: no PTH release even at low Ca levels)
8
Q
Pseudohypopara (PHP)
A
- There is biochemical hypoparathyroidism: hypocalcemia and hyperphosphatemia
- However the PTH level is high
- The causes of the low Ca and high PO4 is due to end-organ resistance to PTH (mutations in GPCRs, may affect other hormones)
- In order for it to be PHP the PTH level MUST be high
9
Q
PHP type Ia
A
- Inactivating mutations of GPCR alpha subunit in numerous hormone receptors
- Causes renal and skeletal PTH resistance
- May see other hormone resistance (TSH, LH, FSH, glucagon)
- There is blunted renal cAMP and phosphaturic response to PTH
- Manifestations: short stature, mild mental retardation, early epiphyseal closure of metacarpals/metatarsals (unique finding: shortened 4th metacarpal)
- AKA Albrights hereditary osteodystrophy (AHO)
10
Q
Other types of PHP
A
- Type Ib: hormone resistance to PTH only, normal alpha subunit activity, no AHO
- Type Ic: resistance to multiple hormones, no alpha subunit inactivity
- Type II: no phosphaturic response to PTH, but normal urine cAMP response
11
Q
Osteomalacia and rickets
A
- Only vitamin D deficiency
- Must be moderate to severe deficiency
- Leads to decreased intestinal Ca absorption, skeletal PTH resistance
- Eventually secondary hyperparathyroidism
12
Q
Hungry bone syndrome
A
- Occurs when there is rapid remineralization of bone, which depletes serum Ca
- Part of the healing phase of hyperpara, hyperthyroidism, bone marrow neoplasia
- Can also occur after Rxing vit D deficiency
- Think of hungry bone syndrome if there are bone mets (prostate, breast, lung) and hypoCa
13
Q
Acute hemorrhagic pancreatitis
A
- Is NOT due to soponification of Ca in pancreas
- Due to multiple factors: pancreatic lipases liberate FFAs which chelate Ca, excessive Ca secretion secondary to high glucagon levels, protease release inhibits PTH release and breaks down PTH
- Can also cause Mg deficiency
- Low Ca secondary to acute hemorrhage pancreatitis is bad prognostic sign
14
Q
Hyperphosphatemia
A
- High levels of PO4 will complex w/ Ca and pull it out of solution
- High PO4 levels also inhibit 1,25OHD production and reduce Ca absorption
- Usually due to excessive PO4 administration, renal failure, cell lysis, hypopara, or PHP
- Rx is to lower serum PO4 levels
15
Q
Signs and Sx of hypoCa
A
- Neuromuscular hyperexcitability: paresthesia (numbness and tingling) of face and extremities, tetany
- Get trousseau’s sign (carpopedal spasm from inflating BP cuff over systolic pressure) and chvostek’s sign (twitching of lip and cheek w/ tapping over facial nerve)
- Neuro: seizures, depression, anxiety, irritability, papilledema, increased ICP
- Derm: dry scaly skin, brittle nails
- Opthalmologic: cataracts
- Calcification of basal ganglia on head Xray
- ALWAYS do ECG if suspicious of hypoCa b/c can cause fatal arrhythmias (longer QT = higher risk)
