Trousseau sign is a physical exam finding that indicates low calcium levels in the blood. First described by French clinician Armand Trousseau in 1861, it involves inflating a blood pressure cuff on the upper arm and watching for involuntary hand spasms within a few minutes. A positive result is one of the most reliable bedside clues that someone has hypocalcemia, with a sensitivity of 94% and specificity of 99%.
How the Test Works
To check for Trousseau sign, a clinician inflates a standard blood pressure cuff on the upper arm to 20 mmHg above the patient’s systolic blood pressure and holds it there for two to three minutes. This temporarily cuts off blood flow to the hand and forearm. If calcium levels are low, the hand will cramp into a distinctive posture within that window.
The characteristic hand position has a French name, “main d’accoucheur” (obstetrician’s hand), because it resembles the hand shape used during childbirth delivery. The knuckle joints flex inward, the fingers straighten out stiffly, and the thumb pulls across the palm in an opposing position. This involuntary spasm is called a carpopedal spasm, and the patient typically cannot relax their hand out of it while the cuff remains inflated.
Why Low Calcium Causes Spasms
Calcium plays a critical role in controlling how easily your nerves fire. When blood calcium drops, nerve cell membranes become more permeable to sodium, which means neurons reach their firing threshold more easily. In practical terms, your nerves become hyperexcitable, ready to fire at the slightest provocation.
The blood pressure cuff adds a second trigger. By blocking arterial blood flow to the hand, it creates brief oxygen deprivation in the tissues below the cuff. That oxygen deprivation further lowers the threshold at which nerves fire. In someone with normal calcium, this mild stress isn’t enough to cause a problem. But in someone whose nerves are already on a hair trigger from low calcium, the combination pushes neurons past their tipping point, producing sustained muscle contractions that lock the hand into that characteristic posture.
What Causes a Positive Result
Hypocalcemia is the primary cause. Trousseau sign typically becomes positive when ionized calcium falls into the range of 1.75 to 2.25 mmol/L, which is below the normal range. Common reasons for low calcium include underactive parathyroid glands (often after thyroid surgery), severe vitamin D deficiency, kidney disease, and certain medications.
Low calcium isn’t the only possibility. Trousseau sign is more specifically tied to a state called “latent tetany,” where muscles are primed to spasm but haven’t yet done so spontaneously. Low magnesium and metabolic alkalosis (when the blood becomes too alkaline) can also produce this state. In rare cases, the sign can appear in people with entirely normal calcium levels, though this is uncommon.
How It Compares to Chvostek Sign
Trousseau sign is often discussed alongside another bedside test called Chvostek sign, which involves tapping the facial nerve in front of the ear and watching for twitching of the lip or cheek muscles. Both tests screen for the same underlying problem: nerve hyperexcitability from electrolyte imbalances.
The key difference is reliability. Trousseau sign is considerably more specific for latent tetany than Chvostek sign, meaning it produces far fewer false positives. Chvostek sign can show up in a significant percentage of people with perfectly normal calcium levels, making it a less trustworthy indicator on its own. When both signs are positive together, the clinical picture becomes more convincing.
What a Positive Sign Means for You
If a clinician checks for Trousseau sign, they likely already suspect an electrolyte problem based on your symptoms. Tingling around the mouth, numbness in the fingertips, muscle cramps, and a feeling of “pins and needles” in the hands and feet are common complaints that prompt this exam. The sign itself is a quick screening tool, not a final diagnosis. A blood test measuring calcium (and often magnesium and albumin) confirms the finding and determines how severe the deficiency is.
Mild hypocalcemia often causes vague symptoms that overlap with anxiety or hyperventilation, which is one reason a simple bedside test like this remains useful. It can point a clinician toward the right blood work before lab results come back, especially in urgent situations where low calcium could progress to more dangerous complications like seizures or heart rhythm abnormalities.