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BICARBONATE (HCO₃⁻)
Q: What is the second most abundant anion in the extracellular fluid (ECF)?
A: Bicarbonate (HCO₃⁻), second to chloride (Cl⁻).
Q: What percentage of total CO₂ does bicarbonate account for?
A: More than 80%.
Q: What is the major function of bicarbonate in the blood?
A: It is a major component of the buffering system.
Q: What happens to bicarbonate in the kidneys?
A: 85% is reabsorbed in the proximal convoluted tubule, and 15% in the distal convoluted tubule.
Q: What condition is associated with increased bicarbonate (↑ HCO₃⁻)?
A: Metabolic alkalosis.
Severe Vomiting, Hypokalemia, Hypoventilation, Excessive alkali intake
Q: What condition is associated with decreased bicarbonate (↓ HCO₃⁻)?
A: Metabolic acidosis.
Hyperventilation
Q: What specimen is used for bicarbonate determination?
A: Serum or plasma (heparinized).
Q: What causes a false decrease in bicarbonate levels?
A: Leaving the sample uncapped, which leads to CO₂ loss.
Magnesium (Mg²⁺)
Q: What is the second most abundant intracellular cation?
A: Magnesium (Mg²⁺), second to potassium (K⁺).
Q: What percentage of magnesium is found in bones, Muscle and other organs and soft tissues, serum and RBC?
A: Bones- 53%.
Muscle and other organs and soft tissues- 46%
Serum and RBC- 1% (33% : Protein bound, 61%: ree or Unionize, 5% : Complex with PO 4 and Citrate)
Q: What is the physiologically active form of magnesium?
A: Free or unionized magnesium (61% of serum Mg²⁺).
Q: What hormone promotes magnesium reabsorption in the kidneys?
A: Parathyroid hormone (PTH).
Q: What hormone increases renal excretion of magnesium?
A: Aldosterone and thyroxine(T4)
Q: What are some causes of hypomagnesemia (↓ Mg²⁺)?
A: Poor diet, chronic alcoholism, diarrhea, diuretics, and hyperaldosteronism.
Q: What are some causes of hypermagnesemia (↑ Mg²⁺)?
A: Renal failure, dehydration, and excessive magnesium intake.
Q: What is the reference method for magnesium determination?
A: Atomic Absorption Spectrophotometry (AAS).
Calcium (Ca²⁺)
Q: What percentage of calcium is found in bones and teeth?
A: 99%.
Q: What is the physiologically active form of calcium?
A: Ionized calcium (Ca²⁺), which makes up 45% of total calcium.
Q: What hormone promotes calcium release from bones into the blood?
A: Parathyroid hormone (PTH).
Q: What hormone inhibits calcium release from bones?
A: Calcitonin.
Q: What are common causes of hypercalcemia (↑ Ca²⁺)?
A: Hyperparathyroidism, malignancy, and vitamin D toxicity.
Q: What are common causes of hypocalcemia (↓ Ca²⁺)?
A: Hypoparathyroidism, vitamin D deficiency, and chronic kidney disease.
Q: What is the reference method for calcium determination?
A: Atomic Absorption Spectrophotometry (AAS).
Phosphate (PO₄³⁻)
Q: Where is most of the phosphate in the body found?
A: 85% in bones.
Q: What hormone decreases renal excretion of phosphate?
A: Growth hormone (GH).
Q: What is the inverse relationship between calcium and phosphate?
A: When calcium levels increase, phosphate levels decrease, and vice versa.
Q: What are some causes of hypophosphatemia (↓ PO₄³⁻)?
A: Hyperparathyroidism, vitamin D deficiency, and antacid use.
Q: What are some causes of hyperphosphatemia (↑ PO₄³⁻)?
A: Hypoparathyroidism, leukemia, and neoplastic disorders.
Lactate (C₃H₆O₃)
Q: What is lactate an indicator of?
A: Oxygen deprivation (hypoxia).
Q: What conditions cause increased lactate levels?
A: Shock, severe infections, metabolic acidosis, and diabetes mellitus.
Q: What specimen is used for lactate determination?
A: Plasma or serum.
Anion Gap (AG)
Q: What is the formula for anion gap calculation?
A: AG = Na⁺ - (Cl⁻ + HCO₃⁻) or AG = (Na⁺ + K⁺) - (Cl⁻ + HCO₃⁻)
Q: What is the normal reference range for anion gap?
A: 7 – 16 mmol/L (without K⁺) or 10 – 20 mmol/L (with K⁺).
Q: What conditions are associated with an increased anion gap (> 20 mEq/L)?
A: Uremia, lactic acidosis, toxin ingestion, and metabolic alkalosis.
Q: What conditions are associated with a decreased anion gap (< 10 mEq/L)?
A: Hypermagnesemia, hypercalcemia, and multiple myeloma.
Q: High Anion gap
A: Increased Organic acid
Q: Normal Anion gap
A: Bicarbonate loss
Q: Normal Anion gap is also referred to?
Hyperchloremic acidosis (Increased chloride reabsorption)
