Clinical Decision Calculators
High-yield clinical decision rules, risk stratification calculators, and laboratory correction formulas tested on COMLEX Levels 1–3 and USMLE Steps 1–3. Includes real-time calculation, risk categorization, and high-yield board review pearls.
CURB-65 Score for Pneumonia Severity
Estimates 30-day mortality in Community-Acquired Pneumonia (CAP) to guide disposition: outpatient vs inpatient vs ICU.
Score 0: Low mortality risk (~0.7%). Patient is suitable for outpatient treatment with oral antimicrobial therapy.
- Outpatient healthy CAP: Amoxicillin 1g TID OR Doxycycline 100mg BID OR Macrolide (Azithromycin/Clarithromycin only if local pneumococcal resistance < 25%).
- Outpatient with comorbidities (COPD, diabetes, CKD, CHF): Augmentin + Macrolide/Doxycycline OR Respiratory Fluoroquinolone monotherapy (Levofloxacin 750mg QD / Moxifloxacin 400mg QD).
- Inpatient ward (CURB-65 ≥ 2): IV Ceftriaxone (or Ampicillin-Sulbactam) + Azithromycin OR Respiratory Fluoroquinolone.
- Inpatient ICU (CURB-65 ≥ 3–5 with septic shock or mechanical ventilation): IV β-lactam (Ceftriaxone) + Azithromycin OR β-lactam + Respiratory Fluoroquinolone. Add Vancomycin or Linezolid if MRSA suspected; add Cefepime/Zosyn/Meropenem if Pseudomonas suspected.
CHA₂DS₂-VASc Score for Atrial Fibrillation
Determines annual stroke risk and necessity of oral anticoagulation (DOAC vs Warfarin) in non-valvular atrial fibrillation.
Score 0 (Men) / 1 (Women): Truly low risk. No oral anticoagulation or antiplatelet therapy recommended.
- Score ≥ 2 in men or ≥ 3 in women: Oral anticoagulation is strongly recommended (Class 1A). Direct Oral Anticoagulants (DOACs: Apixaban, Rivaroxaban, Dabigatran) are superior to Warfarin with lower rates of intracranial hemorrhage.
- Warfarin is mandatory only for: Moderate-to-severe rheumatic mitral stenosis or mechanical prosthetic heart valves (Valvular AFib). DOACs are contraindicated in mechanical valves!
- Aspirin monotherapy or dual antiplatelet therapy (DAPT) is not recommended for stroke prevention in atrial fibrillation.
Wells' Criteria for Pulmonary Embolism
Calculates pretest probability of acute pulmonary embolism to direct diagnostic testing: D-dimer vs CT Pulmonary Angiography (CTPA).
Score ≤ 4.0 (PE Unlikely): Order high-sensitivity D-dimer. If D-dimer is negative (< 500 ng/mL FEU or age-adjusted < age × 10 for age > 50), PE is safely ruled out without imaging.
- Score > 4.0 (PE Likely): Skip D-dimer! Proceed directly to CT Pulmonary Angiography (CTPA). If CTPA is contraindicated (severe renal failure, CrCl < 30, or life-threatening contrast allergy), perform a Ventilation-Perfusion (V/Q) scan.
- Hemodynamically Unstable / Massive PE (SBP < 90): Do NOT transport to CT scanner! Perform bedside Echocardiography (look for RV strain, McConnel sign). If RV strain verified → systemic thrombolysis with IV tPA (Alteplase) or catheter-directed embolectomy.
- In pregnancy with suspected PE: Start with bilateral lower extremity compression ultrasonography. If positive for DVT → treat immediately with LMWH (Enoxaparin) without ionizing radiation.
Corrected Sodium in Hyperglycemia
Corrects measured serum sodium for osmotic water shift into the vascular space during severe hyperglycemia (DKA and HHS).
Initial resuscitation with 0.9% Normal Saline (1–1.5 L in 1st hour). Once volume is restored: if Corrected Sodium is normal or elevated (≥ 135 mEq/L), switch to 0.45% Half-Normal Saline (NaCl) at 250–500 mL/hr to replace free water deficit and prevent hypernatremia. If Corrected Sodium is low (< 135 mEq/L), continue 0.9% Normal Saline.
- Pathophysiology: Hyperglycemia increases extracellular fluid (ECF) osmolality, drawing intracellular water into the intravascular space, diluting serum sodium concentration (pseudohyponatremia or translocational hyponatremia).
- For every 100 mg/dL increment of glucose above 100 mg/dL, serum sodium drops by approximately 1.6 to 2.0 mEq/L.
- Crucial Board Exam Question: When glucose falls below 200 mg/dL in DKA (or 300 mg/dL in HHS), immediately add 5% Dextrose (D5W) to IV fluids while continuing insulin infusion to clear ketones and prevent hypoglycemia or cerebral edema!
Fractional Excretion of Sodium (FEₙₐ) & Urea (FEᵘᵣᵙᵃ)
Differentiates prerenal azotemia from acute tubular necrosis (ATN). FEUrea is the diagnostic test of choice when the patient is taking loop or thiazide diuretics.
FEₙₐ < 1% (0.52%): Indicates intact renal tubular reabsorption of sodium with hypoperfusion (Prerenal Azotemia: volume depletion, dehydration, congestive heart failure, or hepatorenal syndrome). Renal tubules actively conserve sodium (Urine Na < 20 mEq/L).
| Diagnostic Metric | Prerenal Azotemia | Intrinsic ATN |
|---|---|---|
| FEₙₐ (Fractional Excretion Na) | < 1% | > 2% |
| FEᵘᵣᵙᵃ (If on Diuretics) | < 35% | > 50% |
| Urine Sodium (Uₙₐ) | < 20 mEq/L | > 40 mEq/L |
| BUN / Cr Ratio | > 20:1 | < 15:1 |
| Urine Osmolality | > 500 mOsm/kg | < 350 mOsm/kg |
| Sediment | Hyaline casts | Muddy brown casts |
Acid-Base, Anion Gap, Δ/Δ & Winter's Formula
Multi-step acid-base decoding: Anion Gap, Winter's respiratory compensation, and Delta Ratio (ΔAG / ΔHCO₃¯) for triple acid-base disorders.
Primary Metabolic Acidosis with an elevated anion gap of 26 mEq/L (Corrected AG: 26.0). Winter's formula predicted pCO₂ of 29 mmHg matches measured pCO₂ (28 mmHg), indicating appropriate hyperventilation. Delta ratio of 1.2 confirms pure HAGMA (MUDPILES / GOLDMARK etiology).
| Delta Ratio (Δ/Δ) | Underlying Pathology |
|---|---|
| < 0.4 | Pure Normal Anion Gap Acidosis (NAGMA: diarrhea, RTA) |
| 0.4 – 0.8 | Mixed HAGMA + NAGMA (e.g., DKA + severe diarrhea) |
| 1.0 – 2.0 | Pure HAGMA (Lactic acidosis, DKA, Uremia, Toxic Alcohols) |
| > 2.0 | Concurrent Metabolic Alkalosis (vomiting, diuretics) or pre-existing respiratory acidosis |
Glasgow Coma Scale (GCS) & Airway Triage
Standardized neurological consciousness scoring (Eye: 1–4, Verbal: 1–5, Motor: 1–6). Identifies immediate emergency endotracheal intubation thresholds (GCS ≤ 8).
GCS 15 (E4V5M6): Fully alert and conscious. Minimal acute traumatic brain injury risk. Serial neurological exams indicated if intoxicated or on anticoagulants.
Parkland Formula & Burn Fluid Resuscitation
Calculates 24-hour Lactated Ringer's resuscitation for second- and third-degree burns (4 mL × kg × %TBSA). First 50% delivered in first 8 hours post-injury.
Adult Target: 0.5 – 1.0 mL/kg/hr (~35–50 mL/hr).
Pediatric Target (< 30 kg): 1.0 – 1.5 mL/kg/hr.
Electrical Burn with Myoglobinuria: 1.5 – 2.0 mL/kg/hr (target clear urine to prevent acute tubular necrosis from pigment nephropathy).
| Anatomical Region | Adult %TBSA | Infant %TBSA |
|---|---|---|
| Head & Neck (entire) | 9% (4.5% ant / 4.5% post) | 18% (9% ant / 9% post) |
| Anterior Torso (Chest + Abdomen) | 18% | 18% |
| Posterior Torso (Upper + Lower Back) | 18% | 18% |
| Each Upper Extremity (Arm + Forearm) | 9% each (18% total) | 9% each (18% total) |
| Each Lower Extremity (Thigh + Leg + Foot) | 18% each (36% total) | 14% each (28% total) |
| Perineum / Genitalia | 1% | 1% |