Calcium, Ola Elgaddar, 25 11- 2013

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A basic lecture for Chemical Pathology MSc candidates

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Calcium, Ola Elgaddar, 25 11- 2013

  1. 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. 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. 3. BONE 35 % 65 %
  4. 4. Most prevalent body cation
  5. 5. M.W ≈ 40 gm 2.5 mmol / L = ?? mg / dL Mg / dL= 2.5 X 40 / 10 = 10 mg / dL
  6. 6. 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??
  7. 7. Plasma calcium regulation
  8. 8. 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.
  9. 9. Clinical Significance: HYPOCALCEMIA
  10. 10. 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
  11. 11. Adjusted Calcium for Hypoalbuminemia Corrected Total Calcium (mg / dL) = Total Calcium (mg / dL) + 0.8 (4 - Albumin [g / dL])
  12. 12. 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
  13. 13. Hypoparathyroidism & Pseudohypoparathyroidism ???
  14. 14. Clinical Picture
  15. 15. Clinical Significance: HYPOCALCEMIA Lab: - Serum Calcium (Total and ionized) - Renal functions - Albumin - Magnesium - PTH - Vitamin D deficiency
  16. 16. 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
  17. 17. Clinical Picture
  18. 18. 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
  19. 19. Measuring Plasma Calcium: Ionized Calcium Vs Free Calcium ???
  20. 20. Measuring Plasma Calcium: Pre-analytical considerations: Tourniquet: venous occlusion, water efflux & increase protein-bound Ca Fist Clenching: Exercise, Increases Lactate & Lowers pH ??
  21. 21. Measuring Plasma Calcium: Pre-analytical considerations: Posture: - Main problem in hospitalized patients (Hypoalbuminemia) - Standing decreases intravascular water and increases protein-bound Albumin
  22. 22. 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
  23. 23. Measuring Plasma Calcium: Pre-analytical considerations:  Specimen
  24. 24. 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
  25. 25. Measuring Plasma Calcium: Total Calcium: Interference: Lipemia: Ultracentrifugation Icterus: + or – interference (Spectro) Heamolysis: + or – interference (Spectro)  - due to dilution effect?? Magnesium
  26. 26. Measuring Plasma Calcium: Analytical Methods: Free Calcium:
  27. 27. 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.
  28. 28. 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.
  29. 29. 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)
  30. 30. Assignment: Which is better, to measure Total or free calcium? Why? Clinical significance and reference range for urinary Calcium

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