Diabetes mellitus is chronic hyperglycemia from insulin deficiency, resistance, or both. Nurses anchor care on A1c, daily glucose patterns, complication screening, and sick-day readiness — not glucose numbers alone. Connect Diabetes Fundamentals to bedside cues you will reassess first: vitals trends, work of breathing, perfusion, mentation, and pain or ischemic equivalents when relevant. NCLEX items often reward recognizing when subtle instability outweighs reassurance, then selecting nursing actions that protect airway, circulation, and neurologic status before routine tasks.