**Serotonin Syndrome Core Concept**
Serotonin syndrome is a potentially life-threatening medical condition caused by an excess of serotonin in the central nervous system (CNS). It typically occurs as a result of an interaction between certain medications that increase serotonin levels, such as selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), and monoamine oxidase inhibitors (MAOIs).

**Why the Correct Answer is Right**
Serotonin syndrome is characterized by a clinical triad of altered mental status, neuromuscular abnormalities, and autonomic dysfunction. The condition is often precipitated by the concomitant use of multiple serotonergic agents, such as SSRIs, SNRIs, and MAOIs. The pathophysiology of serotonin syndrome involves the excessive stimulation of serotonin receptors, particularly the 5-HT2A receptor subtype, leading to an increase in intracellular calcium levels and subsequent neuronal excitotoxicity.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because serotonin syndrome can be caused by a single serotonergic agent, particularly at high doses or in susceptible individuals.

**Option B:** This option is incorrect because the diagnosis of serotonin syndrome is primarily clinical, relying on the presence of characteristic symptoms such as agitation, confusion, and muscle rigidity, rather than laboratory tests.

**Option C:** This option is incorrect because the treatment of serotonin syndrome involves supportive care, such as hydration and cooling, as well as the discontinuation of offending serotonergic agents, rather than the administration of a specific antidote.

**Clinical Pearl / High-Yield Fact**
A key clinical clue to the diagnosis of serotonin syndrome is the presence of a "triple threat" of altered mental status, neuromuscular abnormalities, and autonomic dysfunction.

**Correct Answer: A. This option is incorrect because serotonin syndrome can be caused by a single serotonergic agent, particularly at high doses or in susceptible individuals.**