Calcium

Question 1

Calcium plays an essential role in many cell functions:

Answer 1

1. Intracellular in muscle contraction and glycogen metabolism
2. Extracellular in bone mineralization
3. In blood coagulation and in transmission of nerve pulses.

Question 2

Calcium is present in plasma in three forms:

Answer 2

free, bound to proteins or complexed with anions as phosphate, citrate
and bicarbonate.

Question 3

Decreased total calcium levels can be associated with

Answer 3

diseases of the bone apparatus (especially osteoporosis),
kidney diseases (especially under dialysis),
defective intestinal absorption and hypoparathyroidism

Question 4

Increased total calcium can be measured in

Answer 4

hyperparathyroidism, malignant diseases with metastases and sarcoidosis.

Question 5

Method

Answer 5

Photometric test using arsenazo III

Question 6

Reagent:

Answer 6

Phosphate buffer
8-Hydroxyquinoline-5-sulfonic acid
Arsenazo III

Question 7

Specimen

Answer 7

Serum, heparin plasma or urine

Question 8

Wavelength

Answer 8

650 nm, Hg 623 nm

Question 9

Conversion factor

Answer 9

Calcium [mg/dL] x 0.2495 = Calcium [mmol/L]
Calcium/U [mg/24 h] x 0.025 = Calcium/U [mmol/24 h]

Question 10

Reference Range

Answer 10

Plasma or serum:
8.6 – 10.3 mg/dL (2.15 – 2.57 mmol/L)

Urine [1]:
Women < 250 mg/24 h (6.24 mmol/24 h)
Men < 300 mg/24 h (7.49 mmol/24 h)

Question 11

Principle

Answer 11

Calcium with arsenazo III at neutral pH yields a blue colored complex, whose intensity is proportional to the calcium concentration. Interference by magnesium is eliminated by addition of 8-hydroxyquinoline-5-sulfonic acid.