Calcium Flashcards
What is calcium for?
Muscle contraction, neural transmission, blood coagulation, enzymatic reactions, structure and blood pressure.
Where is it stored/where does it come from?
99% stored in bone, 1%in blood and ECF
All comes from diet.
What forms is it in in the body?
- Free/ ionized calcium 45%
- Bound to proteins (mostly albumin) 40%
- Complexed to anions (citrate, phos, bicarb, lactate) 15%
Why is ionized calcium best for determining Ca disorders?
It is a more sensitive and specific marker for Ca disorders than total calcium.
Decreased ICA?
Myocardial function is impaired
Neuromuscular irritability - tetany (muscle spasms)
Name 3 hormones involved in calcium regulation.
Parathyroid hormone (PTH) Vitamin D3 (sunlight, diet) Calcitonin (thyroid)
What organs are involved in calcium regulation?
Skeleton, kidneys (hydroxylation of vit D, reabsorption in tubules), Small intestine (absorbs Ca from diet, affected by vit D metabolism)
What affect does PTH have when ICA is decreased?
Bone: activates resorption via osteoclasts.
Kidney: Increases tubular reabsoprtion of Ca in kidney, and excretion of phosphate.
Small intestine: absorption of Ca and vit D(1,25).
Negative feedback; stopped by increased Ca.
What is 1,25-dihydroxy Vitamin D?
Active for of vitamin D3; enhances absoprtion.
Calcitonin
- Sercreted by “C” cells of thyroid.
- Stimulated by increase in blood Ca.
- “Tones” down calcium (inhibits actions of PTH and vit D)
Primary hyoparathyroidism
Lack of PTH, PT gland destruction or removal, vit D metabolism affected.
Hypomagnesemia
Inhibits PTH secrection, impairs PTH action at receptor sites on the bone, causes vit D resistance.
More common in hospitalized patients.
Hypoalbuminemia
Only result reported from total Ca.
Causes: chronic liver disease, nephrotic syndrome and malnutrition.
Acute pancreatitis cause
Hypocalcemia; increase intestinal binding of Ca due to increase in lipase.
Chronic renal disease
Hyperphosphatemia (binds with Ca), due to defective vit D metabolism.
Pseudohypoparathyroidism
PTH reacts normal but target tissues response is impaired.
What patients are at risk for hypocalcemia?
Surgical and the critically ill (due to acid-base imbalances)
Hypocalcemia in neonates
High levels at birth with rapid decline by day 3, adult levels by day 7.
Reduced bone growth and rickets if prolonged.
Hypercalcemia
Hyperparathyroidism, malignancies, hyperthyroidism, increased vit D, thiazide diuretics, prolonged immobilization, multiple myeloma, benign familial hypocalcuria, chronic renal failure.
Conditions increasing risk of osteoporosis
Poor nutrition, vit D disorder, inadequte exercise during growth, endocrine disorders, immobilization, multiple myeloma, heparin therapy, rheumatoid arthritis.
Symptoms of hypercalcemia
Serum Ca >3mmol/L:
- Neurological, GI, renal, increased blood pressure
Treatment of hypercalcemia
Estrogen replacement, parathyroidectomy, increased salt and water intake (increases excretion), bisphosphonates (prevents bone resorption)
What type of specimen is required for total Ca?
Serum or lithium heparin plasma
What type of specimen is required for ICA?
Collect anaerobically, heparinized whole blood preferred, serum from sealed collection tubes if clotted and spun w/in 30 min (tested asap)
Requirements for a urine Ca
Timed and acidified, random for Ca/creat ratios
Methods for total Ca measurement
Reference method: AAS - atomic absorption spectro
Colorimetric: CPC (ortho-cresolphthalein complexone); arsenazo III dye
What interferes with Ca testing?
Hemolysis > 2g/L
Reference ranges for Ca
0-10dys: 1.75-3.0
10dys-12yrs: 2.2-2.7
Adult: 2.15-2.5
24hr urine: 2.5-7.5
Critical: <1.70 or >3.00
ICA reference range
Adult: 1.16 - 1.32
Critical <0.80
