A 56-year-old man with tingling around the mouth and twitching facial muscles likely has which biochemical finding?

The symptoms described—tingling around the mouth and twitching facial muscles—are suggestive of neuromuscular irritability, which commonly occurs in the context of low calcium levels in the blood, or hypocalcaemia. When calcium levels drop below normal, it can lead to increased excitability of nerves and muscles, resulting in symptoms such as paresthesias (tingling sensations) and muscle spasms or twitching, particularly in the facial area, which is known as facial tetany.

Hypocalcaemia can have various causes, including parathyroid hormone dysfunction, vitamin D deficiency, or conditions affecting calcium absorption. The body's calcium levels are crucial for proper neuromuscular function, and a deficiency can disrupt normal signaling and lead to the neurological symptoms noted in this case.

In contrast, other biochemical imbalances, such as hyponatraemia, hypercalcaemia, and hypokalaemia, may have different clinical presentations and are less likely to cause the specific symptoms described. For instance, hyponatraemia typically manifests with confusion, seizures, and altered mental status rather than muscle twitching. Hypercalcaemia can cause muscle weakness and lethargy but is typically not associated with such neuromuscular signs.