Clinical severity markers are objective indicators that help the NP stratify patient acuity, guide treatment intensity, predict outcomes, and determine disposition (outpatient vs. hospitalization vs. ICU). These include biomarkers (measurable substances reflecting disease activity) and clinical scoring systems (validated tools integrating multiple parameters). Key biomarkers: Lactate reflects tissue hypoperfusion (>18.0 mg/dL = abnormal; >4 = severe); procalcitonin indicates bacterial infection severity and guides antibiotic duration; troponin indicates myocardial injury; BNP/NT-proBNP reflects volume overload/heart failure severity; D-dimer indicates fibrin degradation (PE screening); CRP indicates systemic inflammation (nonspecific). Key scoring systems: qSOFA for sepsis screening; CURB-65 for pneumonia severity; HEART score for ACS risk; Wells score for PE probability; APACHE II for ICU severity; NEWS (National Early Warning Score) for deterioration detection. The NP must interpret severity markers in clinical context — no single marker replaces clinical judgment. Trending biomarkers is often more valuable than isolated values.