Quiz 3: Calcium

Question 1

Locations of Ca in the body

Answer 1

• 99%: Bones and teeth as hydroxyapatite

- <1%: Extracellular fluids neuron and muscle firing maintain intracellular levels

Question 2

Ca states in blood

Answer 2

• 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

Question 3

Sources of Error in Ca measurement

Answer 3

• 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.

Question 4

Ca measurement: atomic absorption

Answer 4

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

Question 5

Free Ca Function and Control

Answer 5

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

Question 6

Ca Binding to Protein

Answer 6

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

Question 7

Measuring Free Ca

Answer 7

• 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

Question 8

Ca Reference Values

Answer 8

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)

Question 9

Hypercalcemia/uria (Critical) Values

Answer 9

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

Question 10

Causes of Hypercalcemia

Answer 10

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

Question 11

Primary Hyperparathyroidism

Answer 11

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

Question 12

Malignancy Related Hypercalcemia

Answer 12

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

Question 13

Hypocalcemia Causes and Critical Values

Answer 13

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

Question 14

Calcium regulation

Answer 14

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