Calcium: Regulation, Hypocalcemia, and Hypercalcemia

Calcium is an essential ion that plays a critical role in various bodily functions.

Bone and Teeth Health: Fundamental for maintaining strong bones and teeth.
Muscle and Nerve Conduction: Essential for proper functioning of muscles and nerves.
Clotting: Plays a vital role in the blood clotting process.

Maintaining adequate calcium levels requires a diet rich in calcium. The body has sophisticated mechanisms to regulate blood calcium levels:

Absorption: The gut is crucial for absorbing dietary calcium.
Storage: Excess absorbed calcium is stored in the bones.
Bone Monitoring: Bones actively monitor blood calcium levels. If levels are low (hypocalcemia), bones release stored calcium into the blood to raise levels. However, chronic release can weaken bones over time, leading to conditions like osteoporosis and increased risk of fractures.

Three main factors regulate calcium levels:

Vitamin D: Essential for the absorption of calcium from the gut.
Parathyroid Hormone (PTH): Produced by the parathyroid gland, PTH increases blood calcium levels by stimulating its release from bones, increasing kidney reabsorption, and enhancing intestinal absorption (via Vitamin D activation).
Calcitonin: Produced by the thyroid gland, calcitonin lowers blood calcium levels by inhibiting bone resorption and increasing calcium excretion by the kidneys.

Damage or surgical alteration to the parathyroid or thyroid glands can significantly impact calcium regulation.

A normal calcium level in the blood typically ranges from $8.5 ext{ to } 10.5 ext{ milligrams per deciliter (mg/dL)}$ .

Hypocalcemia occurs when blood calcium levels fall below the normal range, leading to various symptoms primarily affecting muscles and nerves.

Decreased Parathyroid Hormone (PTH): This is often a result of damage to the parathyroid glands, commonly after surgery involving the thyroid (e.g., thyroidectomy), which can inadvertently injure the adjacent parathyroid glands.
Decreased Calcium Intake: Inadequate dietary calcium intake, particularly challenging for individuals with lactose intolerance, necessitates conscious effort to obtain calcium from other sources.
Low Vitamin D Level: Insufficient vitamin D impairs the body's ability to absorb calcium from the diet.
Chronic Kidney Disease: Damaged kidneys may excrete too much calcium, leading to lower blood levels.
Bisphosphonates: These medications, used to treat osteoporosis by strengthening bones, work by decreasing the release of calcium from bones. While beneficial for bone density, they can sometimes cause blood calcium levels to drop too low.
Aminoglycosides: A class of antibiotics (ending in "-mycin," e.g., gentamicin) that cause the kidneys to waste calcium.
Anticonvulsants: Certain anticonvulsant medications, such as phenobarbital, can affect vitamin D levels, indirectly leading to hypocalcemia.

Symptoms mainly involve neurological and muscular excitability due to the role of calcium in nerve conduction and muscle contraction.

C - Convulsions: Seizures can occur due to increased neuronal excitability.
R - Reflexes (Hyperactive): Deep tendon reflexes are hyperactive.
A - Arrhythmias: Can manifest as a prolonged QT interval on an electrocardiogram (EKG) if severely low.
M - Muscle Spasms (Tetany): Involuntary muscle spasms, often in the calves or feet, known as tetany.
P - Positive Signs: Specific physical signs indicate nerve hyperexcitability.
- Trousseau's Sign: To elicit this, a blood pressure cuff is placed on the arm, inflated to a pressure greater than the patient's systolic blood pressure, and left for $3$ minutes. A positive sign is indicated by the hand drawing inward toward the body, with flexion occurring at the wrist, thumb, and metacarpophalangeal (MCP) joints, while the fingers remain extended.
- Chvostek's Sign: This sign indicates nerve hyperexcitability of the facial nerve (cranial nerve VII). It is elicited by tapping over the masseter muscle at the angle of the jaw. A positive sign involves momentary contraction of the facial muscles on the same side that was tapped, such as twitching of the lips.
S - Sensation (Tingling and Numbness): Paresthesia, a sensation of tingling and numbness, typically felt in the fingers and toes.

Interventions:

* Increase intake of calcium-rich foods, such as dairy and leafy green vegetables.

• Vitamin D supplements may be needed to help absorb calcium.

Hypercalcemia occurs when blood calcium levels are excessively high, leading to symptoms primarily affecting general body function.

Overactive Parathyroid (Hyperparathyroidism): Excessive production of PTH leads to an increased release of calcium from bones and enhanced reabsorption, resulting in too much calcium in the blood.
Increased Vitamin D Usage: Overuse of vitamin D supplements can lead to increased calcium absorption and subsequent high blood calcium levels.
Excessive Calcium Supplementation: Consuming too many calcium supplements.
Cancer Spread to Bones (Metastatic Cancer): Certain cancers that metastasize to bones can cause excessive calcium to leak into the bloodstream.
Medications: Some medications can contribute to hypercalcemia.
- Thiazide Diuretics: These diuretics can affect how the kidneys absorb calcium, leading to increased blood levels.
- Lithium: Can indirectly affect parathyroid hormone levels, potentially causing the body to retain too much calcium.

High calcium levels affect various body systems, often leading to generalized weakness and metabolic disturbances.

W - Weakness: Profound muscle weakness is a common symptom.
E - EKG Changes: A shortened QT interval may be observed on an electrocardiogram.
A - Absent Reflexes: Reflexes may be diminished or absent. Patients may also experience altered mental status and abdominal distension due to constipation.
K - Kidney Stone Formation: Patients with hypercalcemia are at an increased risk for developing kidney stones.

INTERVENTION

• IV fluids to promote renal excretion of calcium

• Diuretics (furosemide) to promote renal calcium excretion

• Bisphosphonates (alendronate) to decrease bone reabsorption

• Calcitonin to stimulate renal calcium excretion