calcium, ola elgaddar, 25 11- 2013
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CALCIUM
Ola H. Elgaddar
MBChB, MSc, MD, CPHQ,
LSSGB
Lecturer of Chemical
Pathology
Medical Research Institute
Alexandria University
Ola.elgaddar@alexu.edu.eg
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
35 % 65 %
BONE
Most prevalent body cation
M.W ≈ 40 gm
2.5 mmol / L = ?? mg / dL
Mg / dL= 2.5 X 40 / 10 = 10 mg / dL
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??
Plasma calcium regulation
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.
Clinical Significance:
HYPOCALCEMIA
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
Adjusted Calcium for
Hypoalbuminemia
Corrected Total Calcium (mg / dL) =
Total Calcium (mg / dL) + 0.8 (4 - Albumin [g / dL])
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
Hypoparathyroidism
&
Pseudohypoparathyroidism
???
Clinical Picture
Clinical Significance:
HYPOCALCEMIA
Lab:
- Serum Calcium (Total and ionized)
- Renal functions
- Albumin
- Magnesium
- PTH
- Vitamin D deficiency
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
Clinical Picture
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
Measuring Plasma Calcium:
Ionized Calcium
Vs
Free Calcium
???
Measuring Plasma Calcium: Pre-analytical considerations:
Tourniquet: venous occlusion, water
efflux & increase protein-bound Ca
Fist Clenching:
Exercise,
Increases
Lactate &
Lowers pH
??
Measuring Plasma Calcium: Pre-analytical considerations:
Posture:
- Main problem in hospitalized
patients (Hypoalbuminemia)
- Standing decreases intravascular
water and increases protein-bound
Albumin
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
Measuring Plasma Calcium: Pre-analytical considerations:
Specimen
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
Measuring Plasma Calcium: Total Calcium:
Interference:
Lipemia: Ultracentrifugation
Icterus: + or – interference
(Spectro)
Heamolysis:
+ or – interference (Spectro)
- due to dilution effect??
Magnesium
Measuring Plasma Calcium: Analytical Methods:
Free Calcium:
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.
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.
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)
Assignment:
Which is better, to measure Total
or free calcium? Why?
Clinical significance and
reference range for urinary
Calcium
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