Hypopara is defined as low or absent levels of PTH in the blood, accompanied by low calcium and increased phosphate levels in the blood. The symptoms can vary from mild (such as tingling in the extremities) to severe (such as laryngospasm and seizures).

The leading cause of hypopara is removal of or inadvertent injury to the parathyroid glands during surgery. Following this, up to 25–30% of people will develop transient post-surgical hypopara. This is the absence of PTH or low PTH levels lasting up to 6 months after surgery. If PTH levels are below the normal range for 6 months or longer, this is considered to be chronic post-surgical hypopara.

Delayed hypopara has also been known to affect people years after surgery, but this is very rare. This may be caused by age-related changes to the site of the surgery and the parathyroid gland.