Serum calcium

serum calcium -
moderator Dr.Sahar iqbal consultant chemical pathologist dow university Karachi

1. Serum calcium Dr.Ghulam Murtaza Resident Chemical Pathology DIMC 1

2. Serum calcium CALCIUM is 5 th most common element in the body & most prevalent cation Average human body (70kg ) contain about 1KG or 25 mol, of calcium the skeleton contain 99% of body calcium ( extracellular crystals ) while 1 % is present in soft tissues ,& extra cellular fluid . 2

3. Biochemistry & physiology In blood all calcium is found in plasma with mean concentration of 9.5mg/dl Exits in three physiochemical states in plasma 50 % is free ( ionized ), 40 % is bound to plasma protein & 10 % is complexed with small diffusible inorganic including bicarbonate ,phosphate, lactate ,& citrate 3

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5. The free calcium is biologically active , Its concentration in plasma is regulated by 5

6. Clinical significance Hypocalcemia (< 8.8 mg/dl ) Low total plasma calcium or free ionized calcium or both Hypoalbuminemia is the most apparent of hypocalcemia in hospitalized patient ( Rule of thumb: 0.8 mg/dl Ca change for each 1 gm/dl change in albumin ) 6

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8. Hyper calcemia Two commonest cause of hypercalcemia Malignancy ; in hospitalized patient primary hyperparathyroidism : in out patient Hypercalcemia of malignancy : three types Humoral Hypercalcemia of Malignancy . Tumor secretion of parathyroid related protein Localized osteolytic Hypercalcemia. Metastases with local release of cytokines Increased activated vitamin D . tumor produce 1-alpha hydroxylase which in turn increase activated vit: D 8

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12. Calcium measurement Measurement of Total Calcium : At present two methods are in use 1- Photometric 2- Ion Selective Electrode ISE method has been introduced recently than photometric The specimen is acidified to convert protein bound & complexed calcium to free calcium before calcium is measured by ISE 12

13. In alkaline solution ,the Metal complex dye CPC forms a red chromophore complex with Calcium The color is usually measured at a wave length between 570-580nm The sample is diluted with acid to release complex & protein bound calcium 13

14. Interference by Magnesium is reduced by adding 8-hydroxyquinolone Calcium forms both 1;1 & 2;1 complexes with CPC with former predominately with lower concentration Reaction is temperature sensitive . 14

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16. Total Calcium adjusted for Albumin Corrected total albumin ; (mg/dl ) Total calcium + 0.8 (4 – Albumin (g/dl) ) . Adjusted total mmol/dl Total calcium(mmol) + 0.02 (40-Albumin g/L 16

17. Free Calcium Ionized Ca has been shown to be a more sensitive test for the diagnosis of various calcium disorders 4 . The results are instant as test is done on ISE based systems e.g. electrolyte or ABG analyzers. Composite ABG analyzers should be preferred to give simultaneous estimation of Ca ++ and pH. Reference method for Total Ca is Atomic Absorption photometry but for Ca ++ an ISE based method been developed and approved by IFCC 2 . 17

18. Free Calcium Precautions for Ca ++ are same as for ABG analysis It must be emphasized that factors like tourniquet and patient posture only minimally effect free calcium estimation. Lyophilized Lithium Heparin Syringes or tubes should be used in anaerobic conditions and estimation should be done within 30 min (maximum 1 h). If delayed should be stored at 4 C but then K + estimation is effected. Lyophilized Lithium Heparin Syringes are available in Pakistan and may be used for ABGs and electrolytes 18

19. Effect of pH There is inverse relation between free calcium & pH Free calcium changes by about 5% for each 0.1 unit in change pH Albumin has 30 binding site for calcium binding & account for 80% of the protein bound calcium . Increase in pH increase negative charge on albumin & other proteins leading to increase in protein bound calcium & decrease free calcium 19

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21. Preanalytical factors These factors affect serum total or free Calcium 21 Torniquet & venous occlusion (0.5 to 1mg ) Specimen handling Change in posture 10 -20% increase in total calcium , 5 to 6 % in free calcium binding Alteration in pH (free calcium) Inappropriate anticoagulant Exercise , Spectrometric interference Fist clenching,(dec pH ) Hyperventilation Hemolysis ,Icterus Lipemia

22. Urinary Calcium The rate Urinary calcium excretion reflects Calcium intake ,Intestinal absorption ,skeletal resorption & renal tubular filtration & absorption Healthy men & women excrete up to 300mg of calcium per day on unrestricted diet & up to 200mg p/Day on calcium restricted diet   22

23. Reference intervals 23 Total calcium : Upper limit 10.1 – 10.5 mg /dl Lower limit 8.5 – 8.8 md /dl Free Calcium 4.6 to 5.3 mg/dl (pH 7.4) Urinary Calcium 100mg- 300mg/dl

24. Q : A 46 years male has headaches, fatigue, anorexia, nausea, paraesthesia's, muscular weakness and pain in the extremities. His biochemical profile revealed: Serum Calcium: 2.72 mmol/L (2.10-2.65) Serum Urea: 6.9 mmol/L (3.6-6.6) Blood PTH: 86 pmol/L (15-62) The treating physician wanted to be pretty sure before reaching a diagnosis and advised a repeat profile after one week which showed: Serum Calcium: 2.56 mmol/L (2.10-2.65) Serum Urea: 4.2 mmol/L (3.6-6.6) Blood PTH: 80 pmol/L (15-62) 24

25. Q : Quite puzzled with these lab results, he refers the patient for your expert opinion. What is the most probable diagnosis? Give TWO reasons to support your opinion. What is commonest pathological cause of this disorder? 25

26. Ans : Primary Hyperparathyroidism (1) Fluctuating Calcium levels are typical of Primary Hyperthyroidism. Hypercalcaemia does not follow any ascending pattern with increasing severity of the disease . (2) A higher calcium level should be accompanied by a low PTH. A high PTH with higher or upper normal Calcium levels and normal renal function points towards Primary Hyperthyroidism. Adenoma of Parathyroid gland (85%) 26

27. Hyperparathyroidism (Summary) Primary hyperparathyroidism : most cases (85%) of hyperparathyroidism are the result of a single parathyroid gland malfunctioning and developing into an adenoma. In 15% of cases, multiple adenomas or hyperplasia are involved. Secondary hyperparathyroidism: vitamin D deficiency and chronic kidney disease are the most common causes. Not a parathyroid disease. Tertiary hyperparathyroidism : autonomous production of parathyroid hormone, usually the result of longstanding secondary hyperparathyroidism 27

28. Thank you 28

29. References Tietz text book of clinical chemistry & molecular diagnosis 6 th edition vol; 03 Chemical Pathology for beginners Dr.Aamir Ijaz 29