Explain why irritability is described as a useful clue prompting a broader assessment of underlying mood state, rather than being specific to any one direction of mood disturbance.

Irritability can accompany either low mood or elevated mood states, appearing in severe depression as readily as in mania or hypomania, which means its presence alone does not point toward one specific underlying diagnosis. This makes irritability valuable precisely because it is a nonspecific but reliable signal that something has genuinely changed in a person's emotional baseline, prompting the clinician to look more broadly at the whole clinical picture, energy levels, sleep, mood direction, and associated features, rather than assuming a particular diagnosis based on the irritability itself. Recognising it as a general marker of disturbed mood, rather than a diagnostic feature in its own right, keeps the differential appropriately wide during assessment.