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What may occur as a result of rapid remineralization of bone after surgery or primary hyperparathyroidism?
What may occur as a result of rapid remineralization of bone after surgery or primary hyperparathyroidism?
Which of the following is a cause of hypercalcemia?
Which of the following is a cause of hypercalcemia?
What is the best indicator of calcium status?
What is the best indicator of calcium status?
Which of the following methods is used to measure total serum calcium concentrations?
Which of the following methods is used to measure total serum calcium concentrations?
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What is the preferred specimen for the measurement of total calcium?
What is the preferred specimen for the measurement of total calcium?
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What is commonly used for the rapid measurement of free calcium?
What is commonly used for the rapid measurement of free calcium?
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What affects the binding of calcium by protein and small anions in vitro and in vivo?
What affects the binding of calcium by protein and small anions in vitro and in vivo?
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What is a consequence of vitamin D deficiency?
What is a consequence of vitamin D deficiency?
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What percentage of the body's calcium is stored in the skeleton?
What percentage of the body's calcium is stored in the skeleton?
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What percentage of calcium in plasma is bound to plasma proteins?
What percentage of calcium in plasma is bound to plasma proteins?
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What is the primary mechanism that regulates calcium concentration in plasma?
What is the primary mechanism that regulates calcium concentration in plasma?
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What is a key role of intracellular calcium?
What is a key role of intracellular calcium?
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What is a major function of extracellular calcium?
What is a major function of extracellular calcium?
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What is a cause of hypocalcemia?
What is a cause of hypocalcemia?
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What is a common clinical condition associated with low serum albumin?
What is a common clinical condition associated with low serum albumin?
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What is the term for the condition where total calcium is decreased, but free calcium is normal?
What is the term for the condition where total calcium is decreased, but free calcium is normal?
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What is the effect of increasing the pH of a specimen in vitro on protein-bound calcium?
What is the effect of increasing the pH of a specimen in vitro on protein-bound calcium?
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What is the effect of decreasing the pH of a specimen in vitro on free calcium?
What is the effect of decreasing the pH of a specimen in vitro on free calcium?
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How much does free calcium change for each 0.1 unit change in pH?
How much does free calcium change for each 0.1 unit change in pH?
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Why should specimens be analyzed at the patient's in vivo pH?
Why should specimens be analyzed at the patient's in vivo pH?
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What is the purpose of collecting and handling specimens anaerobically?
What is the purpose of collecting and handling specimens anaerobically?
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Why should syringes and evacuated tubes be filled completely and sealed?
Why should syringes and evacuated tubes be filled completely and sealed?
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How long is free calcium stable in whole blood specimens at room temperature?
How long is free calcium stable in whole blood specimens at room temperature?
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What should be reported on each specimen?
What should be reported on each specimen?
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What is a common source of preanalytical error in calcium measurement?
What is a common source of preanalytical error in calcium measurement?
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What is the effect of forearm exercise on pH and free calcium?
What is the effect of forearm exercise on pH and free calcium?
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What is the reference interval for total calcium in adults?
What is the reference interval for total calcium in adults?
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What is the primary location of organic phosphate in blood?
What is the primary location of organic phosphate in blood?
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What is the effect of hyperventilation on free calcium?
What is the effect of hyperventilation on free calcium?
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What is the form of phosphate measured in serum and plasma by clinical laboratories?
What is the form of phosphate measured in serum and plasma by clinical laboratories?
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What is a major component of hydroxyapatite in bone?
What is a major component of hydroxyapatite in bone?
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What is the effect of tourniquet use on total calcium?
What is the effect of tourniquet use on total calcium?
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Why are hemolyzed specimens unacceptable?
Why are hemolyzed specimens unacceptable?
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What is the effect of hemolysis on inorganic phosphate concentration in specimens?
What is the effect of hemolysis on inorganic phosphate concentration in specimens?
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What is the approximate percentage of total body magnesium found in the skeleton?
What is the approximate percentage of total body magnesium found in the skeleton?
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What is the role of magnesium in enzyme systems?
What is the role of magnesium in enzyme systems?
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What is the effect of reducing serum magnesium concentration on neuromuscular excitability?
What is the effect of reducing serum magnesium concentration on neuromuscular excitability?
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What is a common cause of magnesium deficiency?
What is a common cause of magnesium deficiency?
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What is a common association with magnesium deficiency?
What is a common association with magnesium deficiency?
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What is the normal reference interval for serum phosphate in adults?
What is the normal reference interval for serum phosphate in adults?
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Study Notes
Calcium
- Calcium is the fifth most common element in the body and the most prevalent cation.
- The skeleton contains 99% of the body's calcium.
- Calcium exists in three physicochemical states in plasma:
- 50% is free (ionized)
- 40% is bound to plasma proteins, primarily albumin
- 10% is complexed with small anions
- Calcium is redistributed among these three plasma pools, acutely or chronically, by:
- Alterations in the concentration of protein and small anions
- Changes in pH
- Changes in the quantities of free calcium and total calcium in the serum
Regulation of Calcium
- Calcium concentration in plasma is tightly regulated by hormones:
- Parathyroid hormone (PTH)
- 1,25(OH)2D
- Intracellular calcium has key roles in many important physiological functions, including:
- Muscle contraction
- Hormone secretion
- Glycogen metabolism
- Cell division
- Extracellular calcium is needed for:
- Bone mineralization
- Blood coagulation
- Stabilizing plasma membranes and influencing permeability and excitability
Hypocalcemia
- Hypocalcemia (low total serum calcium) may be due to:
- A reduction in the albumin-bound calcium
- A reduction in the free fraction of calcium, or both
- Common clinical conditions associated with low serum albumin include:
- Chronic liver disease
- Nephrotic syndrome
- Congestive heart failure
- Malnutrition
Measurement of Calcium
- Methods used to measure total serum concentrations of calcium include:
- Spectrophotometric methods
- Ion-specific electrode (ISE) methods
- Atomic absorption methods
- Samples should be collected and handled anaerobically to minimize alterations in pH and free calcium.
- Free calcium is measured in heparinized whole blood, and is reported in mmol/L.
Phosphate
- Phosphorus in the form of inorganic and organic phosphate is an important and widely distributed element in the human body.
- Inorganic phosphate is the fraction measured in serum and plasma by clinical laboratories.
- Phosphate in plasma exists as anions in the form of:
- Monovalent (H2PO4)
- Divalent (HPO4)
- Phosphate is a major component of hydroxyapatite in bone and is also found in soft tissue.
- Most of the phosphate in soft tissue is incorporated into nucleic acids, phospholipids, phosphoproteins, and high-energy compounds, such as adenosine triphosphate (ATP).
Interferences and Reference Intervals
- Hemolysis, icteric, and lipemic specimens can interfere with phosphate measurement.
- Reference interval for serum phosphate in adults is 0.81 to 1.45 mmol/L.
Magnesium
- Magnesium is the fourth most abundant cation in the body, with approximately 55% in the skeleton and 45% intracellular.
- Magnesium functions as a cofactor for more than 300 enzymes and is required for enzyme-substrate complex formation.
- Magnesium is an allosteric activator of many enzyme systems and competitively inhibits the entry of calcium into neurons.
- Reducing the serum magnesium concentration results in increased neuromuscular excitability.
Hypomagnesemia/Magnesium Deficiency
- Hypomagnesemia often reflects a shift of magnesium into cells without replacement.
- Moderate or severe magnesium deficiency is usually due to gastrointestinal (GI) tract or kidney losses.
- Magnesium deficiency is commonly associated with:
- Diarrhea
- Excessive urinary losses of magnesium from the kidneys in:
- Alcoholism
- Diabetes mellitus (osmotic diuresis)
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Description
This quiz covers the regulation of calcium levels in the body, including hypocalcaemia and hypercalcemia, and their causes and effects.
