Trace Elements and Bone Mineral Metabolism

Define trace elements

Characterized by their presence in the body at very low concentrations

State the units of measure used for trace elements and ultratrace elements

micrograms per deciliter (µg/dL).

Elements found at even lower concentrations, specifically in nanograms per deciliter (ng/dL), are referred to as ultratrace elements

List the two methods routinely used to measure trace elements

• atomic absorption spectroscopy

• inductively coupled mass spectrometry

Discuss the special pre-analytical and analytical considerations for measuring trace elements

Pre-analytical - Contamination control

Analytical - specialized methodology - AAS and MS

Compare and contrast essential, possibly essential, and non-essential trace elements

• a lack in the diet leads to specific signs and symptoms of deficiency - iron, zinc, copper, iodine, and selenium

• known to be essential in other animals, but their specific role or necessity in humans has not yet been clearly defined - arsenic, boron, and lithium

• A lack of these elements in the diet does not result in symptoms of deficiency - aluminum, mercury, and silver

For each of the following trace elements, state its biological role (if any), if it is essential, and two symptoms associated with deficiency and/or toxicity (as applicable)

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Aluminum

• Non-Essential

• no deficiency symptoms

• dementia, seizures, and motor dysfunction

Antimony

• Non-essential

• No deficiency symptoms

• ECG changes, chronic cardiac failure, pulmonary effects and local epithelium irritation

Arsenic

• Non-essential

• No deficiency symptoms

• gastrointestinal (nausea/vomiting), cardiovascular, renal (renal failure); dermatologic (alopecia), hepatic (cirrhosis), involve the central nervous system (tremors)

Beryllium

• Non-essential

• No deficiency symptoms

Cadmium

• Non-essential

• No deficiency symptoms

Chromium

Cobalt

Copper

Fluorine

Manganese

Mercury

• Non-essential

• No deficiency symptoms

Molybdenum

Nickel

• Non-essential

• Skin rash, eczema, dermatitis, and/or hair loss

Selenium

Thallium

• Non-essential

• No deficiency symptoms

Zinc

State the distribution of calcium, phosphorus, and magnesium within an adult

Calcium

• Bone 98%

• ECF 2%

• Plasma - 3 forms: Free or ionized 50%, complexed with anions, bound to plasma proteins

Phosphorus

• Bone 85%

• Other tissues 15%

Magnesium Distribution

• between bone and soft tissue

• The second most abundant intracellular cation

• plasma - ionized, protein-bound, complexed

Discuss the relationship between pH and calcium binding

• Inversely proportional

  • pH level changes, the amount of calcium bound to proteins and anions shifts in the opposite direction, which directly impacts the concentration of free (ionized) calcium

  • pH increase = calcium decrease

  • pH decrease = calcium increase

State the form of plasma calcium that is physiologically active

• Free or ionized - makes up 50% of total calcium in plasma

Recall the biological function and homeostatic regulation of calcium, phosphorus, magnesium and vitamin D

maintain skeletal integrity and cellular function

• Calcium

  • skeletal mineralization, blood coagulation, and nerve impulse transmission

    . It also acts as a cofactor for certain enzymes and preserves cell membrane integrity

  • Managed by parathyroid (stimulates bone resorption, increases calcium reabsorption in kidneys, triggering vitamin d3 synthesis) and calcitonin (inhibits bone reabsorption and tubular reabsorption in the kidneys), and vitamin D

• Phosphorus

  • structural component of bones and teeth, and an essential part of cell membranes, critical for the storage and transfer of energy (ATP), contributes to enzyme function, and serves as a building block for DNA and RNA

  • Levels are maintained through a balance of intestinal absorption, renal excretion, and exchange with the bone reservoir

• Magnesium

  • second most abundant intracellular cation and a vital cofactor in reactions involving ATP

  • exchange between gastrointestinal absorption, renal excretion, and the exchangeable magnesium pool in the bones

• Vitamin D

  • increases bone resorption by stimulating osteoclasts. It also plays a role in the synthesis of neurotransmitters

  • synthesized in the skin via sunlight, then processed by the liver and finally the kidneys into its most active form, 1,25-dihydroxy vitamin D3. This final activation step in the kidneys is stimulated by PTH

Describe how changes to PTH or calcitonin will impact calcium homeostasis

PTH

The overall effect of increased PTH is a rise in plasma calcium and a decrease in phosphorus

• increases blood calcium when levels are too low

Calcitonin

The overall effect of calcitonin secretion is a reduction in the concentration of ionized calcium in the plasma

• lowers blood calcium when levels are too high

Outline the physiological pathway of Vitamin D, starting with 7-Dehydrocholesterol and ending in 1,25-dihydroxy Vitamin D3

• Skin: The process begins in the skin, where 7-dehydrocholesterol is converted into Vitamin D3 (cholecalciferol) through exposure to sunlight.

• Liver: Vitamin D3 then travels to the liver, where it undergoes its first hydroxylation to become 25-hydroxy vitamin D3.

• Kidneys: This intermediate form is transported to the kidneys for the final conversion into 1,25-dihydroxy vitamin D3, which is the most active form of the vitamin.

  • This final activation step in the kidneys is specifically stimulated by Parathyroid Hormone (PTH).

Once synthesized, 1,25-dihydroxy vitamin D3 works to increase the intestinal absorption of calcium and phosphorus and stimulates osteoclasts to metabolize bone calcium, effectively enhancing the effects of PTH

Differentiate between D3 and D2 forms of vitamin D

Source Origin: Vitamin D3 is primarily found in animal-sourced foods (such as fatty fish or egg yolks) and is the version produced naturally by the human body.

In contrast, Vitamin D2 is derived from plant sources, such as mushrooms exposed to UV light, and is commonly used in fortified foods and supplements.

Lists three causes and symptoms of hypercalcemia

1. Malignancy: This includes osteolytic hypercalcemia, where a tumor directly breaks down bone, and humeral hypercalcemia, where chemicals from a tumor cause bone breakdown

2. Primary Hyperparathyroidism

3. Renal Failure

Symptoms

1. disorientation, lethargy, confusion, or depression

2. constipation, nausea, and vomiting

3. formation of kidney stones

Differentiate osteolytic and humeral forms of hypercalcemia seen in malignancies

how the tumor causes bone breakdown

• Osteolytic Hypercalcemia: In this form, the tumor directly breaks down the bone. This localized destruction releases calcium into the bloodstream.

• Humeral Hypercalcemia: In this form, a chemical substance secreted by the tumor (traveling through the blood like a hormone) causes the bone to break down

List three causes and symptoms of hypocalcemia

Causes

1. Hypoparathyroidism

2. Decreased Vitamin D

3. Inadequate Diet

Symptoms

1. Tetany

2. Muscle cramps

3. Seizures

State the appropriate sample types used for total calcium determinations

• Serum

• Lithium heparin plasma

• 24-hour urine collected with an HCl preservative

Discuss the impact EDTA anticoagulants has on total calcium determinations

This is because EDTA works by chelating (binding) calcium, which would interfere with the measurement and lead to inaccurate results.

Discuss the CPC and Arsenzo III dye methods of Total Calcium determinations

CPC

• calcium is placed in an alkaline solution where it reacts with the CPC reagent. This chemical reaction results in the formation of a red complex. The intensity of the color is then measured using a spectrophotometer at a wavelength between 570 and 580 nm

Arsenzo III dye method

• The Arsenzo III method involves the dye forming a complex directly with the calcium in the sample. Unlike the CPC method, the resulting complex is measured at a higher wavelength of 650 nm

State the specimen requirements for a free/ionized calcium

All samples must be kept anaerobic and analyzed immediately

• Plasma

• Serum

• Heparinized whole blood

Discuss the method used to measure free/ionized calcium

ion-selective electrodes (ISE)

• Selective Binding: The electrode's membrane is designed to selectively and reversibly bind calcium ions from the specimen.

• Electrical Potential: As these calcium ions bind to the membrane, an electrical potential develops.

• Proportionality: This potential is directly proportional to the concentration of ionized calcium present in the sample, allowing for an accurate quantitative reading

State the reference range for total and free/ionized calcium and phosphorus

4.60–5.08 mg/dL, - half of total calcium

List two causes of hyperphosphatemia and hypophosphatemia

hyperphosphatemia

• decreased renal excretion

• Increased intake of phosphorus

hypophosphatemia

• Increased urinary excretion

• Decreased intestinal absorption

Discuss the method and specimen types used to determine phosphorus concentrations

Analytical Methods

• the formation of an ammonium phosphomolybdate complex

  • measured in UV absorption and Colorimetric

• Specimen types

  • Serum or lithium heparin plasma

Describe the diurnal variation of phosphorus

Phosphorus levels in the body naturally fluctuate throughout the day, which can impact the interpretation of results

List two causes of hypermagnesemia and two causes of hypomagnesemia

hypermagnesemia

• Excessive intake

• Acute or chronic renal failure

Hypomagnesemia

• Reduced intake

• decreased absorption

Discuss the calmagite, formazan dye, and methylthymol blue methods and specimen types used to determine phosphorus concentrations

Magnesium

• Calmagite Method: Magnesium ions (Mg2+) bind with calmagite to form a reddish-violet complex, which is measured at a wavelength of 532 nm.

• Formazan Dye Method: Magnesium ions bind with the dye to produce a colored product that is read at 660 nm.

• Methylthymol Blue Method: Magnesium ions bind with this chromogen to form a colored complex

Specimen types

• Serum or heparinized plasma

For comparison, the sources state that phosphorus concentrations are actually determined by the formation of an ammonium phosphomolybdate complex. This complex is either:

• Measured directly via UV absorption at 340 nm.

• Reduced to molybdenum blue and measured between 600 and 700 nm

Identify the cause of abnormal calcium, phosphorus, or magnesium results when provided a case study

1. Analyzing Abnormal Calcium Results

• Hypercalcemia (High Ca):

  • Primary Hyperparathyroidism: Caused by overactive parathyroid glands.

  • Malignancy: Look for osteolytic (direct bone destruction) or humeral (chemical-driven destruction, common in Multiple Myeloma). A key clue is often an elevated Alkaline Phosphatase (ALP).

  • Renal Failure: The kidneys fail to properly regulate calcium balance.

  • Symptoms to look for: Confusion, kidney stones, nausea, or a history of fractures.

• Hypocalcemia (Low Ca):

  • Hypoparathyroidism: Insufficient PTH production.

  • Vitamin D Deficiency: Leads to conditions like Rickets in children or Osteomalacia in adults.

  • Secondary Factors: Check for low Magnesium or Albumin levels, or signs of malabsorption.

  • Symptoms to look for: Tetany, muscle cramps, or seizures.

• Ionized Calcium Shifts: If only ionized calcium is abnormal, check the patient's pH. Alkalosis (high pH) increases binding and decreases ionized calcium, while acidosis (low pH) increases it.

2. Analyzing Abnormal Phosphorus Results

• Hyperphosphatemia (High P): Most commonly caused by decreased renal excretion (acute or chronic renal failure) or excessive phosphorus intake.

• Hypophosphatemia (Low P): Look for causes related to increased urinary excretion, decreased intestinal absorption, or internal redistribution.

• Note: Phosphorus and calcium often have an inverse relationship due to PTH, which generally increases plasma calcium while decreasing phosphorus.

3. Analyzing Abnormal Magnesium Results

• Hypermagnesemia (High Mg): Often tied to renal failure or excessive intake (e.g., antacids or IV administration). Symptoms include hypotension and decreased reflexes.

• Hypomagnesemia (Low Mg): Usually results from reduced intake or decreased absorption. Symptoms include hypertension, arrhythmia, and muscle cramps.

4. Assessing Metabolic Bone Diseases

• Paget’s Disease: Indicated by excessive bone breakdown/reforming and significantly elevated ALP.

• Osteoporosis: Characterized by a loss of bone mass (osteoclastic activity exceeding osteoblastic activity), often manifesting as a "Dowager’s Hump" or height loss.

• Rickets/Osteomalacia: Specifically tied to Vitamin D deficiency, leading to bone softening and physical deformities like bowed legs.

5. Potential Pre-Analytical Errors (False Results)

If the clinical symptoms do not match the laboratory results, consider these source-documented errors:

• Hemolysis: Falsely elevates magnesium and phosphorus because both are highly concentrated inside cells.

• Contamination: Trace element results (measured in μg/dL or ng/dL) are easily skewed by common materials like phlebotomy supplies, glassware, or lab air.

• Collection Errors: Total calcium results will be invalid if collected in an EDTA tube, as EDTA chelates calcium