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Flashcards in Quiz 3: Calcium Deck (14)
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Locations of Ca in the body

- 99%: Bones and teeth as hydroxyapatite
- <1%: Extracellular fluids neuron and muscle firing maintain intracellular levels


Ca states in blood

- 45%: Free unbound (Ionized)*
- 45%: Bound to proteins (albumin)
- 10%: Bound to anions *(bicarbonate, citrate, lactate, phosphate etc) that pass through glomerulus
Most measuring methods find total Ca, including protein-bound Ca


Sources of Error in Ca measurement

- Drawing blood in tube with EDTA, citrate, oxalate anticoagulant which binds Ca.
- Use of tourniquet and venous occlusion will increase total calcium levels.
- Heparin must be lyophilized, liquid heparin can dilute.


Ca measurement: atomic absorption

Photometric with specific calcium binding dyes
1.CPC (o-cresolphthalein complexone) red dye at 570 -580 nm (Hydroquiniline is added to remove Mg++)
2. Arsenazo III blue dye at 650 nm


Free Ca Function and Control

Is the biologically active form of calcium whose levels are controlled by hormones.


Ca Binding to Protein

Binding of calcium to proteins in plasma is pH dependent.
- Alkalosis increases binding=free Ca++ down
- Acidosis decreases binding=free Ca++ up
Can be affected by:
- Alb/Globulin ratio
- Abnormal proteins
- pH (acidosis/alkalosis)
- Bilirubin (displacement from albumin)
- Drugs


Measuring Free Ca

- Ion Selective Electrode (ISE): electrode with a calcium selective membrane, a reference electrode (Ag/AgCl), and a reference solution (Calcium chloride) are used
+ Change in potential due to Ca++ at the membrane is measured and converted to concentration with an activity coefficient.
- pH dependent
- Not stable
- Colormetric: Ca reacts with o-cresolphthalein


Ca Reference Values

Calcium, Total: 8.6 - 10.0 mg/dL, 2.15 – 2.50 mmol/L
Calcium, Ionized: 4.6 - 5.3 mg/dL, 1.16 - 1.32 mmol/L
CSF: 4.2 - 5.4 mg/dL
Urine: 100 - 300 mg/d (avg diet)


Hypercalcemia/uria (Critical) Values

Total > 11.0 mg/dL
- Critical > 13.5 mg/dL
Ionized > 1.33 mmol/L
- Critical > 1.50 mmol/L
Uria > 300 mg/day


Causes of Hypercalcemia

Primary hyperparathyroidism -55%
Malignancy (cancer with bone metastasis ie multiple myeloma) – 35%
Other – 10 %
- Hyperthyroidism
- Medications: thiazide, lithium
- Vitamin D: excess
- Acute or Chronic Renal Failure - excretion impaired
- Burnett’s syndrome -Milk-alkali syndrome
*Use PTH to help differentiate between these causes


Primary Hyperparathyroidism

Most common cause of increased CA
Defect in Parathyroid glands
Usually due to adenoma(s) in glands


Malignancy Related Hypercalcemia

Parathyroid hormone-related protein (PTHrP) has similar structure to PTH, produced by benign and malignant tumors, acts like PTH and increases Calcium
- Can be assayed if humoral hypercalcemia is suspected


Hypocalcemia Causes and Critical Values

Causes tetany (uncontrolled muscle spasms), possible seizures
Hypoparathyroidism— decreased PTH
Pseudohypoparathyroidism—impaired response of target organ to PTH
Magnesium deficiency-leads to low PTH
Vitamin D deficiency or malabsorption
Renal disease: Low Albumin (Total Calcium)
- (For every 1 g/dL Albumin, the CA will decrease by approx. 0.8 mg/dL) ( 1g for 1 mg)
Total < 8.6
Panic < 6.5 mg/dL


Calcium regulation

Controlled by PTH (increases CA), Vitamin D (increases absorption in intestines, and Calcitonin (decreases bone reabsorption)