Calcium-Phosphorus Relationship and Calcium Imbalance

Calcium-Phosphorus Relationship

  • Serum Calcium: 9.0−11.09.0-11.0 mg/dL

  • Serum Phosphorus: 3.0−4.53.0-4.5 mg/dL

  • Calcium and magnesium move in the same direction.

  • Low magnesium can lead to low calcium due to reduced PTH release/action.

Hypocalcemia Signs

  • Chvostek's sign: tapping on the facial nerve causes a twitch.

  • Trousseau's sign: carpal spasm upon inflation of a blood pressure cuff to 20 mm Hg above systolic BP for 3-5 minutes.

  • Cardiovascular signs: Prolonged QT interval, decreased myocardial contractility, arrhythmias (bradycardia to ventricular tachycardia and asystole).

  • Mental signs: Depression, emotional instability, anxiety, psychosis.

Hypercalcemia Causes

  • Primary Hyperparathyroidism: Increased PTH production, leading to increased calcium release from bone, intestinal absorption, and renal reabsorption.

  • Malignancies: Breast cancer, lung cancer, multiple myeloma, lymphoma.

  • Immobilization: Bone mineral loss, leading to elevated calcium levels and potential renal stones.

  • Drugs: Thiazide diuretics, lithium, calcium supplements, high doses of vitamin A or D.

Hypercalcemia Effects

  • Neuromuscular: Muscle weakness, decreased deep tendon reflexes due to reduced neuromuscular excitability.

  • GI symptoms: Constipation, vomiting, nausea due to decreased motility; Pancreatitis.

  • Behavioral changes: Lethargy, drowsiness, irritability, depression, psychosis, stupor, coma.

  • Cardiac function: Stabilizes cardiac membrane, reducing excitability; positive inotropic effect (stronger contractions).

  • Renal changes: Polyuria, hypercalciuria leading to renal stones.

  • Cardiovascular changes: Arrhythmias, heart block, shortened QT interval, increased digitalis sensitivity, hypertension.

Calcium Measurement

  • Total calcium in plasma: 8.9–10.38.9 – 10.3 mg/dL.

  • Corrected calcium level calculation: Measured serum calcium + 0.8X(4.00.8 X (4.0 – measured serum albumin g/dL) in hypoalbuminemia.

Hormonal Regulation

  • PTH (Parathyroid Hormone): Increases plasma calcium levels by promoting calcium transfer from bone, intestinal absorption, and renal reabsorption.

  • Calcitonin: Decreases calcium levels by inhibiting bone resorption; produced in the thyroid.

  • Calcitriol: Increases calcium levels by promoting calcium absorption from the intestine, enhancing bone resorption, and stimulating renal tubular reabsorption; synergistic effect with PTH.

Hypocalcemia

  • Total calcium level less than 8.98.9 mg/dL

  • Ionized calcium concentration less than 4.64.6 mg/dL.

Hypocalcemia Clinical Signs

  • Neuromuscular: Tetany (spontaneous muscle contractions), Tingling sensations, Hyperactive deep tendon reflexes, Convulsions, Muscle cramps, Chvostek and Trousseau signs.