A basic lecture for Chemical Pathology MSc candidates

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