PTH, Minerals, Vit D Flashcards
Pt has c/o mild fatigue and an elevated serum Ca of 11.5. What is the most likely cause of this patient’s hypercalcemia? Would you order any other lab tests?
Hyperparathyrdoidism?
PTH
PO4
A PTH of 165 is?
HIGH!
normal 15-75
A PO4 of 2.8 is?
low
normal 2.5-4.5
What is the MCC of hypercalcemia in an outpatient setting?
primary hyperparathyroidism
What are the top three causes of primary elevation of PTH?
– 85% benign parathyroid neoplasm or adenoma – 10% parathyroid hyperplasia (3% MEN)
– 2% parathyroid carcinoma
**Usually doesn’t cause serum Ca >12 mg
What percentage of patient’s with primary hyperparathyroidism have bones, stones, groans and moans?
<20%! Most people are asymptomatic
Usually in F in pts >45 yrs, otherwise similar sex diffs
In addition to PTH and PO4 what other lab tests hsould you order?
urine Ca (24 hr preferred)
How do you evaluate hypercalcemia?
Total Ca >10.5 or ionized Ca >5.6 > causative diseases vs meds > measure intact PTH level > normal/high > 24 hr urine Ca level
If 24 hr urine Ca is low….
familial hypocalciuric hypercalcemia
If 24 hr urine Ca is normal/high…
primary/tertiary hyperparathyroidism
Describe Ca equilibria in blood
High pH: Ca is bound to PROTEIN (albumin, globulins) 40-45%
Lower pH: Free (ionized)
Complexed: PO4, HCO3, Lactate (5-10%)
*All are pH dependent
What happens to free Ca in alkalemia?
HIGHER pH –> free Ca decreases, increase in Pr-bound Ca
What happens to free Ca in acidemia?
LOWER pH –> free Ca increases, Pr-bound Ca decreases
For each .1 change in pH, free Ca changes by ….
Does total Ca change?
5%
NO!
What is the major clinical utility of ionized Ca?
- Ensure maintenance of hemodyanmic fxn
- monitor pts in critical care
- higher mortality in septi pts with hypocalcemia
- neonates
- pts w/ pancreatitis/renal disease - diagnose/treat hypercalcemic/hypocalcemic conditions
What reflects TRUE Ca status, is unaffected by protein concentration and requies stringent collection/handling because its pH sensitive?
Free (ionized Ca)
What reflects (free + protein-bound + anion bound), depends on protein concentration and is not affected by pH?
Total Ca
What formula is often use to correct Ca to account for protein?
Corrected Ca (mg/dL) = Measured Total Ca (mg/dL) + 0.8*[4-Albumin (g/dL)] • Correction fails to accurately predict calcium status in individual patients
How do you correct iCa for pH changes?
Corrected iCa = Measured iCa [1-0.53(7.4-measured pH)]
- Limited range of correction (pH 7.2-7.6)
- Assumptions: patient has pH of 7.4, no variation in albumin, no additional iCa binding proteins or anions
- Preferable to avoid pre-analytical issues entirely
When should iCa be tested?
total Ca is <8 or >10.2
How can parathyroidectomies be guided by serum PTH concentrations?
• Decrease in PTH of > 50% 10 minutes post-resection signals success in removing the abnormally secreting parathyroid tissue
• Rapid turnaround time is essential
– Shorter incubation
– Compromised sensitivity