Mineral Disorders - 4th Year Medicine

Mineral Disorders - Overview

• Course: 4th Year Medicine, Laboratory Medicine Course
• Instructor: Jehad Tayyeb, Clinical Biochemistry Department
• Year: 2023

Intended Learning Outcomes

• Students will understand normal and abnormal levels of plasma magnesium, sodium, potassium, and calcium.
• Students will be able to explain disorders associated with abnormal mineral levels.
• Students will learn about common laboratory tools for estimating mineral concentrations.

Magnesium (Mg)

• Fourth most abundant cation (Mg²⁺) in the body.
• Total body content: 21-28 g
• Normal serum Mg: 1.7-2.5 mg/dL
• Distribution:
  • 53% stored in bone
  • 46% in muscles and soft tissues
  • 1% extracellularly in blood and RBCs

Magnesium (Mg) Functions

• Crucial for muscle and nerve function
• Forms a complex with ATP, acting as a cofactor for various enzymes, transporters, and nucleic acids
• Required for normal cellular function, replication, and energy metabolism
• Important for the metabolism of sodium, potassium, calcium, vitamin C, and phosphorus
• Maintains electrolyte balance
• Has anti-stress properties

Hypomagnesemia

• Clinically significant deficiency: <1.2 mg/dL
• Renal causes:
  • Hypercalcemia
  • Tubular disorders in the kidney
  • Hyperaldosteronism
  • Diuretics
• Extrarenal causes:
  • Malnutrition
  • Malabsorption, chronic diarrhea, or laxative abuse
  • Increased cell uptake of Mg
  • Increased storage in bone seen after parathyroidectomy

Hypermagnesemia

• Rare, primarily in patients with renal failure using Mg-containing drugs.

Blood Sodium

• Plasma level: 132-144 mmol/L
• Daily requirements: 5-15 g in the form of NaCl
• Excretion: About 95% of sodium is excreted in urine.

Sodium Distribution and Functions

• About one-third of total body sodium is in the skeleton.
• Most sodium is found in extracellular fluids.
• Associated with chloride and bicarbonate for acid-base balance regulation.
• Essential for maintaining body fluids and protecting against excess fluid loss.
• Influences normal muscle irritability and cell permeability.

Causes of Hypernatremia

• Rapid administration of sodium salt
• Hyperactivity of adrenal cortex (Cushing's disease)
• Administration of corticotrophin (ACTH), cortisone
• Dehydration (e.g., diabetes insipidus)

Causes of Hyponatremia

• Adrenocortical insufficiency (increased sodium loss)
• Chronic renal failure
• Liver cirrhosis
• Congestive heart failure
• Excess loss of gastrointestinal fluids (severe diarrhea)
• Excess sweating

Blood Potassium

• Red blood cells contain significant potassium.
• Normal plasma potassium: 3.6-4.8 mmol/L
• Principal intracellular cation but also important in extracellular fluid for influencing muscle activity, especially cardiac muscles.
• Essential for regulating acid-base balance.
• Required for protein synthesis, glycogenesis, and glycogenolysis.

Causes of Hyperkalemia

• Renal failure
• Dehydration
• Adrenal insufficiency (Addison's disease)
• Symptoms include central nervous system symptoms and cardiac issues (bradycardia, poor heart sounds, vascular collapse, cardiac arrest). Other symptoms include mental confusion, numbness, weakness of respiratory muscles, and paralysis.

Causes of Hypokalemia

• Chronic diseases with malnutrition
• Gastrointestinal losses (vomiting, diarrhea)
• Overactive adrenal cortex (Cushing's syndrome)
• Use of diuretics (e.g., acetazolamide, chlorothiazide)
• Symptoms include muscle weakness, irritability, paralysis, and tachycardia

Calcium Distribution

• 99% of body calcium is stored in bone and teeth.
• 1% is intracellular (mainly in mitochondria and endoplasmic reticulum).
• 0.1% is extracellular (plasma calcium 9-11 mg/dL).

Calcium Functions

• Major mineral in bone and teeth
• Essential for nerve impulse transmission
• Important in muscle contraction
• Required for enzyme activation
• Crucial for blood clotting

Hypocalcemia

• Decrease in plasma calcium level below 9 mg/dL
• Causes:
  • Hypoparathyroidism
  • Vitamin D deficiency
  • Low serum albumin
  • Hypomagnesemia
  • Medullary carcinoma of the thyroid
  • Chronic renal insufficiency
  • Malabsorption
  • Alcoholism

Hypercalcemia

• Increase in plasma calcium level above 11 mg/dL
• Causes:
  • Primary hyperparathyroidism
  • Secondary hyperparathyroidism (e.g., in renal failure)
  • Vitamin D toxicity
  • Tumors producing PTH-related proteins
  • Bone metastasis

Laboratory Tools for Mineral Levels

• Spectrophotometer.
• Routine Automated Biochemistry Analyzers
• Blood test (needle to draw blood from veins)
• Urine test (quantitative analysis of urine samples)
• Red blood cell test ("gold standard" for evaluating mineral deficiency

Spectrophotometer Operation Steps

• Warm-up (15 min)
• Set wavelength
• Wipe cuvette with reference solution
• Place cuvette into sample holder, close cover
• Set absorbance to zero
• Remove reference tube, add standard and sample tubes
• Read and record absorbance
• Calculate sample concentration

Concentration Calculation Formula:

• C_test = (A_test / A_standard) x C_standard