Ionised Calcium Measurement Quiz

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Questions and Answers

What effect does an increase in pH have on ionised calcium measurements?

Alters the measurement accuracy without changing calcium levels

Has no effect on ionised calcium measurements

Increases ionised calcium measurements

Decreases ionised calcium measurements (correct)

What calculation is used to adjust calcium levels when albumin is low?

[Ca] + 0.02(40-albumin) (correct)

[Ca] + 0.1(40-albumin)

[Ca] - 0.1(40-albumin)

[Ca] - 0.02(40-albumin)

What is the primary reason for measuring ionised calcium?

Determining parathyroid function

Assessing bone density

Diagnosing symptoms of hypocalcaemia and hypercalcaemia (correct)

Evaluating kidney function

Which condition is likely to cause an increase in ionised calcium levels?

Acidosis Signup and view all the answers

How can laboratories improve accuracy in measuring ionised calcium?

By correcting ionised calcium for pH Signup and view all the answers

Which of the following conditions is NOT typically associated with calcium metabolism disorders?

Chronic bronchitis Signup and view all the answers

What is the primary action of parathyroid hormone (PTH) in relation to calcium homeostasis?

Increase calcium release from bones Signup and view all the answers

What is a crucial factor in collecting serum for ionized calcium analysis?

Maximally filling the serum separator tube Signup and view all the answers

Which statement correctly describes the calcium flux in a healthy adult?

The exchange in bone surfaces is not illustrated in the diagram Signup and view all the answers

Which element is NOT typically involved in calcium homeostasis regulation?

Cortisol Signup and view all the answers

What role does calcitriol play in the absence of parathyroid hormone (PTH)?

Increases plasma phosphate concentration Signup and view all the answers

Which of the following is a cause of hypercalcaemia associated with malignancy?

PTHrP production Signup and view all the answers

Which condition is least commonly associated with hypercalcaemia?

Chronic kidney disease Signup and view all the answers

What is the effect of hypophosphataemia on FGF23 release?

Decreases FGF23 release from bone Signup and view all the answers

What characterizes primary hyperparathyroidism?

Can be sporadic or familial Signup and view all the answers

What is the primary effect of PTH on plasma calcium levels?

Increases plasma calcium concentration Signup and view all the answers

How does PTH influence phosphate levels in the plasma?

Decreases plasma phosphate concentration Signup and view all the answers

Which organ is stimulated by PTH to enhance calcium reabsorption?

Kidney Signup and view all the answers

What is the net effect of PTH on the body's acid-base balance?

Results in mild acidosis Signup and view all the answers

What role does calcitonin play in calcium homeostasis?

Inhibits osteoclast activity Signup and view all the answers

What triggers the secretion of FGF23?

Increased phosphate and calcitriol levels Signup and view all the answers

Which of the following describes FGF23's primary effect?

Decreases serum phosphate Signup and view all the answers

What is the role of 1α-hydroxylation in relation to PTH?

Activates calcitriol for calcium and phosphate absorption Signup and view all the answers

What condition stimulates the release of PTH?

Hypocalcemia Signup and view all the answers

In which way does mild acidosis relate to the actions of PTH?

It results from the physiological responses to PTH Signup and view all the answers

What is the most common cause of primary hyperparathyroidism?

Parathyroid adenoma Signup and view all the answers

In which population is primary hyperparathyroidism most frequently observed?

Postmenopausal women Signup and view all the answers

What physiological response occurs in response to hypocalcaemia?

Increase in parathyroid hormone (PTH) Signup and view all the answers

What condition may lead to tertiary hyperparathyroidism?

Renal failure Signup and view all the answers

What is a significant effect of hyperphosphataemia on vitamin D metabolism?

Inhibits the 1α-hydroxylation of 25-hydroxycholecalciferol Signup and view all the answers

What would be an appropriate management approach for hyperphosphataemia?

Phosphate binders Signup and view all the answers

Which of the following conditions can potentially result from severe hypophosphataemia?

Cardiac arrest Signup and view all the answers

What is the definitive treatment for primary hyperparathyroidism?

Surgical removal Signup and view all the answers

Study Notes

Calcium, Magnesium, and Phosphate Homeostasis

Calcium, Magnesium, and Phosphate are critical for many bodily functions, including bone health, nerve and muscle function, and enzyme activity.
Their homeostasis (balance) is maintained by hormones and other processes to ensure proper levels in the body.
Imbalances can lead to various health conditions.

Measurement of Calcium in the Blood

Analytical measurement of calcium in the blood is crucial.
Factors like albumin concentration affect total calcium measurements.
Corrected/adjusted calcium levels account for these factors.
The formula used for adjusting calcium levels for low albumin is [Ca] + 0.02(40-albumin).

Functions of Calcium

Calcium plays a crucial structural role in bones and teeth.
It enables neuromuscular excitability, muscle contraction, and neurotransmitter release.
Calcium serves as a cofactor for various enzymes, including coagulation factors.
Calcium is an intracellular signaling molecule.

Calcium Fractions

Total calcium in plasma ranges from 2.25 to 2.60 mmol/L.
A proportion of calcium is in a diffusible form (54%) with a free (physiologically active) portion of 47%.
A portion of calcium is complexed (with citrate, phosphate) with 7% of it bound to other compounds
Non-diffusible calcium is protein-bound (46%).

pH and Ionized Calcium

pH affects calcium binding to proteins.
Increased pH (alkalosis) leads to greater calcium binding to proteins, decreasing free ionized calcium.
Decreased pH (acidosis) reduces calcium binding to proteins, increasing free ionized calcium levels.

Indications for Measuring Ionized Calcium

Chronic kidney disease and dialysis
Transplantation procedures
Extracorporeal (external) blood transfusing
Massive blood transfusions
Critical illnesses
Post-operative periods (following parathyroidectomy)
Severe pancreatitis
Hypercalcemia due to malignancy

Pre-analytical Variables for Ionized Calcium

Stasis-free collection method should be used for collecting blood samples.
Use of Serum separator tubes (SST) is necessary
Samples should be maximally filled.
Transport blood samples on ice.
Reaching the lab within 30 mins is optimal for separating red blood cells (RBCs) within an hour (centrifugation).
Tubes should be kept sealed to avoid changes in pH and ensure accurate measurements.

Ionized Calcium Measurement Methods

Most laboratories use a blood gas analyzer for measuring total calcium.
Ion-selective electrodes are often used for measuring ionized calcium.
Accurate measurement of ionized calcium requires excluding air from the sample and maintaining consistent pH levels.

Calcium Flux

Calcium fluxes are the continuous movement of Calcium throughout the body, including bone, intestine, kidney, and other tissues.
Multiple processes contribute to overall calcium balance.

Hormones Regulating Calcium Homeostasis

Parathyroid hormone (PTH) plays a key role.
Vitamin D, in its active form (calcitriol), regulates calcium absorption and mobilization.
Calcitonin has a less significant role.

PTH Precursors and Cleavage Products

PTH (parathyroid hormone) is produced through multiple stages: pre-pro-PTH and pro-PTH.
Intact PTH is an active form while other fragments of PTH are not actively regulating calcium homeostasis

Actions of PTH

PTH affects calcium homeostasis in bone, kidney, and gut.
These target organs are key in maintaining healthy calcium levels through either conservation or secretion.

Vitamin D Metabolism

Vitamin D plays a crucial role in calcium absorption from the gut.
Its synthesis and activation in the kidneys is essential.
PTH and FGF23 impact the activity of calcitriol in different parts of the body.

Circulating Concentrations of Vitamin D Metabolites

Circulating concentrations of Vitamin D metabolites, like calciferol and 25-hydroxyvitamin D, vary based on factors like season, pregnancy, and puberty.
The majority of vitamin D is bound to DBP, while a smaller amount is bound to albumin.

Calcitonin Action

Calcitonin inhibits osteoclast activity and decreases bone resorption.
It plays a lesser role compared to PTH and vitamin D in regulating calcium homeostasis.

Fibroblast Growth Factor 23 (FGF23)

FGF23 is secreted by osteocytes.
It reduces serum phosphate and calcitriol levels.
It affects kidney function in the way phosphate reabsorption is controlled.

Homeostatic Responses to Hypocalcemia/Hypophosphataemia

Processes responsible for maintaining calcium and phosphate are activated to respond to the shortage in calcium and phosphate in the blood
These hormones ensure that plasma levels are normalized.

Causes of Hypercalcemia

Primary hyperparathyroidism, malignancy, granulomatous diseases, vitamin D toxicity, and other factors can cause hypercalcemia.

Causes of Hypocalcemia

Hypoparathyroidism, vitamin D deficiency, hypomagnesemia, and other factors can lead to hypocalcemia.

Causes of Hyperphosphatemia

Renal insufficiency and elevated phosphate intake are common causes of hyperphosphatemia.

Causes of Hypophosphatemia

Various factors, including nutrient deficiencies and loss from the body, can lead to hypophosphatemia

Magnesium Physiology

Urinary excretion controls magnesium concentration in extracellular fluid
Hypomagnesemia can mimic hypocalcemia
Magnesium deficiency occurs often with prolonged diarrhea and malabsorption.

Investigation of Hyper/Hypocalcemia

A specific algorithm can be followed to identify the cause of a particular condition based on plasma calcium levels (high or low).

Regulation of Parathyroid Hormone

Parathyroid glands are activated as needed.
Normal calcium homeostasis is maintained by the parathyroid hormone's action.

Regulation of Vitamin D

Vitamin D is activated and synthesized as needed to control calcium absorption from food sources and/or stored in the body.
PTH and FGF23 impact the activation of calcitriol in different parts of the body.

Clinical Features of Hypercalcemia/Hypocalcemia/Hyper/Hypophosphatemia/Hypo/Hypermagnesemia

Various symptoms can accompany these imbalances, including neuromuscular issues, gastrointestinal problems, neurological impairments, etc.

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Description

Test your knowledge on ionised calcium measurements and their clinical implications. This quiz covers various factors affecting calcium levels, the role of parathyroid hormone, and common disorders associated with calcium metabolism. Perfect for healthcare professionals and students in the field of biochemistry.