Hypocalcemia and Tetany: Symptoms, Causes, and Treatment Guide

Hypocalcemia is a medical condition characterized by abnormally low levels of calcium in the blood, typically defined as serum calcium below 8.5mg/dL (2.12mmol/L). When calcium drops, nerves and muscles become hyper‑excitable, often leading to tetany, a syndrome of involuntary muscle cramps, spasms, and tingling sensations.

Why Calcium Matters

Calcium Ca²⁺ is the most abundant mineral in the body, essential for bone strength, blood clotting, and transmitting electrical signals in nerves and muscles. About 99% of the body’s calcium resides in bones, while the remaining 1% circulates in the extracellular fluid where it directly influences cell excitability.

Key Hormones and Vitamins that Regulate Blood Calcium

Parathyroid hormone (PTH) is released by the four parathyroid glands in response to low serum calcium. PTH raises calcium by stimulating bone resorption, increasing renal reabsorption, and activating vitamin D in its active form, calcitriol, which boosts intestinal calcium absorption.

If any part of this loop falters-whether the glands produce insufficient PTH, the kidneys can’t convert vitamin D, or the gut fails to absorb-serum calcium can fall, setting the stage for tetany.

Common Causes of Hypocalcemia

Understanding the root triggers helps clinicians target treatment. The most frequent culprits include:

• Post‑surgical hypoparathyroidism: Accidental removal or damage to parathyroid tissue during thyroid or neck surgery.
• Vitamin D deficiency: Limited sun exposure, malabsorption syndromes (celiac, Crohn’s), or chronic kidney disease that impairs activation.
• Magnesium deficiency (hypomagnesemia) reduces PTH secretion and impairs its action - a classic but often missed cause.
• Renal failure: Kidneys lose the ability to convert vitaminD and excrete phosphate, leading to secondary hypocalcemia.
• Acute alkalosis: Shifts calcium from ionized (active) to protein‑bound form, lowering the biologically available fraction.
• Medications: Loop diuretics, bisphosphonates, and some anticonvulsants can deplete calcium or interfere with vitaminD metabolism.

How Low Calcium Triggers Tetany

Calcium stabilizes neuronal membranes. When ionized calcium plunges, voltage‑gated sodium channels open more readily, causing spontaneous depolarizations. The clinical picture of tetany reflects this heightened excitability:

• Paresthesias: Tingling around the mouth, fingertips, and toes.
• Muscle cramps: Particularly in the calves, hands, and neck.
• Carpopedal spasm: A classic hand‑claw sign where the wrist flexes and fingers extend.
• Facial grimacing (Chvostek sign) when tapping the facial nerve.
• Seizures or cardiac arrhythmias in severe cases.

These signs can appear suddenly after surgery, during heavy vomiting (loss of magnesium), or in chronic kidney disease patients.

Diagnosing Hypocalcemia and Tetany

Laboratory work‑up focuses on confirming low ionized calcium and uncovering the underlying driver.

1. Serum total calcium measures both bound and free calcium. Values < 8.5mg/dL suggest hypocalcemia.
2. Ionized calcium is the physiologically active fraction. This test is more accurate, especially in acid‑base disorders.
3. PTH level: Low PTH points to hypoparathyroidism; high PTH indicates secondary causes.
4. 25‑OH vitaminD and 1,25‑OH vitaminD to assess deficiency.
5. Serum magnesium and phosphate: Hyperphosphatemia often co‑exists with renal failure.
6. ECG may reveal a prolonged QT interval, a red flag for arrhythmia risk.

Treatment Strategies

The goal is two‑fold: quickly raise ionized calcium to stop acute symptoms, then correct the underlying disorder to prevent recurrence.

Acute Management

For severe tetany or ECG changes, give intravenous calcium:

Calcium gluconate is the preferred first‑line agent because it’s gentler on peripheral veins. After the bolus, a continuous infusion may be needed to maintain levels.

Long‑Term Management

• Oral calcium supplements (500-1000mg elemental calcium daily) divided into two doses.
• Active vitaminD analogs (calcitriol 0.25-0.5µg daily) to boost gut absorption.
• Magnesium repletion if serum Mg < 1.7mg/dL, typically with magnesium sulfate or oxide.
• Address the root cause: surgical revision for hypoparathyroidism, phosphate binders for renal patients, or adjusting offending medications.

Prevention Tips for At‑Risk Individuals

People with a history of neck surgery, chronic kidney disease, or malabsorption should keep a few habits:

• Regularly monitor serum calcium, magnesium, and vitaminD (every 6-12months).
• Maintain adequate dietary calcium - dairy, fortified plant milks, leafy greens - aiming for 1000-1200mg/day.
• Get safe sun exposure or a vitaminD supplement (800-1000IU/day for most adults).
• Stay hydrated and avoid excessive alkaline drinks that could shift calcium.

Related Conditions and When to Seek Help

Low calcium doesn’t exist in a vacuum. It often overlaps with other electrolyte disorders:

• Hypercalcemia: Opposite problem, causes fatigue, polyuria, and kidney stones.
• Hypomagnesemia: Can coexist and worsen hypocalcemia.
• Metabolic alkalosis: Common after prolonged vomiting; correct with chloride‑rich fluids.

If you notice tingling, muscle cramps, or a prolonged QT on your heart monitor, call your physician immediately. Untreated tetany can progress to seizures or life‑threatening arrhythmias.

Key Takeaways

The hypocalcemia‑tetany connection boils down to calcium’s role in nerve‑muscle stability. Pinpointing why calcium is low-whether it’s surgical, renal, vitaminD‑related, or magnesium‑driven-guides both urgent treatment and long‑term prevention. With timely labs, appropriate IV calcium, and targeted supplements, most patients bounce back without lingering issues.