Calcium is essential for bone mineralization and plays an important role in many physiological processes; it is tightly regulated by parathyroid hormone and vitamin D. Hypocalcemia can result from hypoalbuminemia, chronic kidney disease, hypoparathyroidism, or hypomagnesemia, while hypercalcemia is usually caused by primary hyperparathyroidism or certain cancers. Both total and ionized calcium levels should be measured and interpreted carefully due to various pre-analytical factors that can affect results.

1. CALCIUM
Ola H. Elgaddar
MBChB, MSc, MD, CPHQ,
LSSGB
Lecturer of Chemical
Pathology
Medical Research Institute
Alexandria University
Ola.elgaddar@alexu.edu.eg

2. ILOs
After this lecture you should be able to
 Describe bone components
 Understand the biochemistry and
physiology of Calcium
 Differentiate between hypo and
hypercalcemia;
causes,
clinical
picture and lab diagnosis
 Illustrate
pre-analytical
and
analytical aspects of serum and
urinary calcium measurement

3. BONE
35 %
65 %

5. Most prevalent body cation

6. M.W ≈ 40 gm
2.5 mmol / L = ?? mg / dL
Mg / dL= 2.5 X 40 / 10 = 10 mg / dL

8. Biochemistry & Physiology
 Exists in the 3 mentioned
states.
 The free portion is the active
form.
 Tightly regulated by PTH and
Vit D.
 Effect of pH??

9. Plasma calcium regulation

10. Physiologically:
Intracellular Ca:
- 1/10000 of extracellular
- Physiological functions:
Muscle contraction, glycogen
metabolism & cell division
Extracellular Ca:
- Provides calcium ion for the
maintenance of intracellular calcium
- Bone mineralization, blood
coagulation & plasma membrane
potential.

11. Clinical Significance:
HYPOCALCEMIA

12. Clinical Significance:
HYPOCALCEMIA
Causes:
Hypoalbuminemia:…….Causes??
(Why?)
Pseudohypocalcemia???
- Decreased total and normal free
calcium??
1 g / dL of albumin binds
approximately 0.8 mg / dL of
calcium

13. Adjusted Calcium for
Hypoalbuminemia
Corrected Total Calcium (mg / dL) =
Total Calcium (mg / dL) + 0.8 (4 - Albumin [g / dL])

14. Clinical Significance:
HYPOCALCEMIA
Causes:
CRF: (Why?)
Hypoproteinemia
Hyperphosphatemia
Low serum 1,25(OH) Vit D
Skeletal resistance to PTH
Hypomagnesemia: (Why?)
Impairs PTH secretion
PTH end-organ resistance

15. Hypoparathyroidism
&
Pseudohypoparathyroidism
???

16. Clinical Picture

17. Clinical Significance:
HYPOCALCEMIA
Lab:
- Serum Calcium (Total and ionized)
- Renal functions
- Albumin
- Magnesium
- PTH
- Vitamin D deficiency

18. Clinical Significance:
HYPERCALCEMIA
Causes:
 Hyperparathyroidism:
- Most common cause in out patients
- Due to adenoma, hyperplasia or
cancer.
- Mechanism?
 Malignancy:
- Most common cause in hospitalized
patients
- Due to excessive bone resorption

19. Clinical Picture

20. Clinical Significance:
HYPERCALCEMIA
Lab:
- Serum Calcium (Total and ionized)
- PTH
- Vitamin D
- PTHrP
• Parathyroid H. related peptide
• Secreted from solid tissue malignancies
• Binds to PTH receptors stimulating
bone resorption

21. Measuring Plasma Calcium:
Ionized Calcium
Vs
Free Calcium
???

22. Measuring Plasma Calcium:
Pre-analytical considerations:
Tourniquet: venous occlusion, water
efflux & increase protein-bound Ca
Fist Clenching:
Exercise,
Increases
Lactate &
Lowers pH
??

23. Measuring Plasma Calcium:
Pre-analytical considerations:
Posture:
- Main problem in hospitalized
patients (Hypoalbuminemia)
- Standing decreases intravascular
water and increases protein-bound
Albumin

24. Measuring Plasma Calcium:
Pre-analytical considerations:
Prolonged immobilization:
- Increase bone resorption
- Which form of calcium increases?
 Hyperventilation:
- Increases pH and so……??
 Diurnal variation:
- Both free calcium concentration and
excretion decreases by night

25. Measuring Plasma Calcium:
Pre-analytical considerations:
 Specimen

26. Measuring Plasma Calcium:
Analytical Methods:
Total Calcium:
 Photometric:
- Cresolphthalein method
(Interference???)
- Arsenazo III Method
 Atomic absorption Spectrometry:
Reference method according to CLSI
 Ion Selective Electrode

27. Measuring Plasma Calcium:
Total Calcium:
Interference:
Lipemia: Ultracentrifugation
Icterus: + or – interference
(Spectro)
Heamolysis:
+ or – interference (Spectro)
 - due to dilution effect??
Magnesium

28. Measuring Plasma Calcium:
Analytical Methods:
Free Calcium:

29. Measuring Plasma Calcium:
Free Calcium:
Increasing the pH of a specimen in
vitro increases the ionization and
negative charge on albumin and
other proteins, leading to an increase
in protein-bound calcium and a
decrease in free calcium, and the
reverse is true.

30. Measuring Plasma Calcium:
Free Calcium:
- Free calcium changes by about 5%
for each 0.1 unit change in pH
- Specimens must be analyzed at the
patient's pH in vivo, requiring that all
specimens be handled to prevent
alterations in pH.

31. Measuring Plasma Calcium:
Reference intervals:
Total Calcium:
8.5 - 10.5 mg / dL
(???? Mmol / L)
Free Calcium:
1.15 – 1.33 mmol / L
(???? Mg / dL)

32. Assignment:
Which is better, to measure Total
or free calcium? Why?
Clinical significance and
reference range for urinary
Calcium