Tetany is a condition where your nerves and muscles become abnormally excitable, causing involuntary spasms, cramping, and tingling. It’s most commonly triggered by low calcium levels in the blood, though shifts in blood pH and deficiencies in magnesium can also set it off. The hallmark sign is painful, uncontrollable contractions of the hands and feet, but symptoms can range from mild numbness around the mouth to severe complications like seizures and difficulty breathing.
Why Tetany Happens
Your nerves rely on a precise balance of minerals, especially calcium, to fire correctly. Calcium helps regulate how easily a nerve sends a signal to a muscle. When the level of ionized calcium (the active, free-floating form in your blood) drops too low, nerves begin firing on their own without any intentional signal from the brain. The result is spontaneous muscle contractions you can’t control.
Tetany typically doesn’t occur unless ionized calcium falls below about 1.1 mmol/L, which corresponds roughly to a total serum calcium of 7.0 to 7.5 mg/dL. For reference, the normal range for total calcium is about 8.5 to 10.5 mg/dL, so a meaningful drop is required before symptoms appear.
Importantly, your total calcium level on a blood test can look normal while the ionized portion is actually low. This happens during alkalosis, when the blood becomes more alkaline than usual. In that environment, more calcium binds to proteins and becomes inactive, leaving less ionized calcium available to stabilize nerve signaling.
Common Causes
The most frequent triggers fall into a few categories: hormonal problems, nutritional deficiencies, and changes in breathing patterns.
- Parathyroid dysfunction. The parathyroid glands control calcium levels. When they’re damaged or removed during thyroid surgery, calcium can plummet. Post-surgical hypoparathyroidism is one of the most well-recognized causes of severe tetany.
- Vitamin D deficiency. Vitamin D drives calcium absorption in the gut. Without enough of it, even an adequate dietary calcium intake won’t keep blood levels stable. Severe deficiency can lead to recurrent episodes of tetany.
- Low magnesium. Magnesium plays a supporting role in calcium metabolism. When magnesium drops below about 0.8 mEq/L, it reduces the body’s ability to respond to parathyroid hormone and worsens calcium loss. This means magnesium deficiency can both cause tetany on its own and make existing low calcium harder to correct.
- Hyperventilation. Breathing too fast or too deeply, often from anxiety or pain, blows off carbon dioxide and makes the blood more alkaline. This respiratory alkalosis shifts calcium into its bound, inactive form, effectively creating temporary low calcium without any actual calcium loss. It’s one of the most common causes of mild tetany in otherwise healthy people.
- Gut absorption problems. Conditions like celiac disease and other intestinal disorders can impair absorption of calcium, magnesium, and vitamin D simultaneously. In some cases, tetany with combined electrolyte deficiencies is the very first sign of an undiagnosed digestive condition.
What Tetany Feels Like
Symptoms exist on a spectrum from subtle to severe. The mildest form is tingling or numbness, usually around the lips, fingertips, and toes. Many people describe a “pins and needles” sensation in the hands and face as the earliest warning sign.
As calcium drops further, muscle cramps and twitching develop. The characteristic feature is carpopedal spasm: the wrists flex sharply, the fingers draw together, and the ankles and toes curl inward. These spasms are painful and can last minutes to hours. In severe cases, tetany can progress to generalized muscle cramping throughout the body, laryngospasm (tightening of the vocal cords that makes breathing difficult), seizures from blood vessel constriction in the brain, and even effects on the heart.
Manifest vs. Latent Tetany
Doctors distinguish between two forms. Manifest tetany involves obvious, visible spasms and is usually caused by significant drops in calcium, most often after parathyroid surgery. It’s relatively rare but hard to miss.
Latent tetany, sometimes called spasmophilia, is far more common and much subtler. People with latent tetany don’t have spontaneous spasms but are on the edge of neuromuscular irritability. The underlying mechanism often involves hyperventilation or mild magnesium deficiency rather than a dramatic calcium crash. Symptoms tend to be vague: frequent muscle cramps, tingling, fatigue, and a feeling of tightness. Because none of these symptoms is specific, latent tetany can be difficult to diagnose and is often mistaken for anxiety or other conditions.
How Tetany Is Detected
Beyond blood tests for calcium, magnesium, and vitamin D, two bedside tests can reveal neuromuscular irritability even when visible spasms aren’t present.
The Chvostek sign involves tapping on the facial nerve just in front of the ear. In a positive test, the muscles on that side of the face twitch involuntarily. It’s a quick screening tool, but not perfectly reliable. About 25% of healthy people with normal calcium will test positive, and roughly 29% of people with confirmed low calcium won’t produce the sign at all.
The Trousseau sign is considered more reliable. A blood pressure cuff is inflated on the upper arm above systolic pressure and held for a few minutes. If the hand curls into a characteristic spasm (the same carpopedal posture described above), the test is positive. This occurs because the cuff briefly reduces blood flow and oxygen to the nerves in the arm, pushing already-irritable nerves past their threshold.
How Tetany Is Treated
Treatment depends on the severity. For someone hyperventilating in an emergency room, simply slowing their breathing can resolve the alkalosis and restore normal ionized calcium levels within minutes. Breathing into cupped hands or using guided breathing techniques helps carbon dioxide levels return to normal.
When true low calcium is the cause, the approach is more direct. In mild cases, oral calcium and vitamin D supplements can gradually restore levels. In severe situations, with spasms, laryngospasm, or seizures, calcium is given intravenously in a hospital setting. The goal is to raise ionized calcium quickly enough to stop dangerous symptoms while the underlying cause is identified and addressed.
If magnesium is also low, correcting it is essential. Without adequate magnesium, calcium replacement alone often fails because the body can’t properly regulate calcium or respond to its own parathyroid hormone. Both deficiencies need to be treated together for symptoms to fully resolve.
Long-term management depends entirely on the root cause. Someone with permanent hypoparathyroidism after surgery will need lifelong calcium and vitamin D supplementation. A person with celiac disease may see tetany resolve once they adopt a gluten-free diet and their gut begins absorbing nutrients normally again. For those whose episodes are triggered by hyperventilation, learning to recognize and control breathing patterns can prevent recurrence entirely.