Clinical Decision Calculators

PULMONOLOGY / IM / ED Pneumonia Severity Score

CURB-65 Score for Pneumonia Severity

Estimates 30-day mortality in Community-Acquired Pneumonia (CAP) to guide disposition: outpatient vs inpatient vs ICU.

0 / 5

Low Risk (0.7% Mortality)

C — Confusion

New disorientation in person, place, or time (AMTS ≤ 8)

U — Urea (BUN > 19 mg/dL)

Blood urea nitrogen > 19 mg/dL (> 7 mmol/L)

R — Respiratory Rate ≥ 30 /min

Tachypnea ≥ 30 breaths per minute

B — Blood Pressure (SBP < 90 or DBP ≤ 60)

Hypotension: Systolic < 90 mmHg OR Diastolic ≤ 60 mmHg

65 — Age ≥ 65 Years

Patient is 65 years of age or older

Disposition Recommendation & Evidence-Based Action

Score 0: Low mortality risk (~0.7%). Patient is suitable for outpatient treatment with oral antimicrobial therapy.

COMLEX / USMLE High-Yield Board Pearls:

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.

CARDIOLOGY / HEMATOLOGY AFib Thromboembolic Risk

CHA₂DS₂-VASc Score for Atrial Fibrillation

Determines annual stroke risk and necessity of oral anticoagulation (DOAC vs Warfarin) in non-valvular atrial fibrillation.

0 pts

Low Risk (0.2% annual stroke)

C — Congestive Heart Failure (+1)

Clinical CHF or objective LVEF ≤ 40%

H — Hypertension (+1)

Resting BP > 140/90 or receiving antihypertensives

Age < 65 years (+0)

A — Age 65–74 years (+1)

A₂ — Age ≥ 75 years (+2)

D — Diabetes Mellitus (+1)

Fasting glucose > 126 mg/dL, HbA1c ≥ 6.5%, or on insulin/oral hypoglycemics

S₂ — Prior Stroke / TIA / Thromboembolism (+2)

History of ischemic stroke, transient ischemic attack, or systemic embolism

V — Vascular Disease (+1)

Prior myocardial infarction, peripheral artery disease (PAD), or aortic plaque

Sc — Sex Category: Female (+1)

Biological female gender

Anticoagulation Guideline (AHA/ACC/ACCP 2023 Guidelines)

Score 0 (Men) / 1 (Women): Truly low risk. No oral anticoagulation or antiplatelet therapy recommended.

High-Yield Board Takeaway:

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.

EMERGENCY MED / CRITICAL CARE Pretest Probability for PE

Wells' Criteria for Pulmonary Embolism

Calculates pretest probability of acute pulmonary embolism to direct diagnostic testing: D-dimer vs CT Pulmonary Angiography (CTPA).

0.0 pts

PE Unlikely (≤ 4.0)

Clinical Signs & Symptoms of DVT (+3.0)

Unilateral leg swelling, calf tenderness, asymmetric circumference (> 3cm)

Alternative Diagnosis Less Likely than PE (+3.0)

PE is the most likely diagnosis based on clinical picture

Heart Rate > 100 beats/min (+1.5)

Sinus tachycardia is the most common ECG finding in PE

Immobilization ≥ 3 Days or Surgery in Last 4 Weeks (+1.5)

Bed rest ≥ 3 days, long-haul travel, or general/orthopedic surgery

Previous Objective DVT or PE (+1.5)

Prior documented deep vein thrombosis or pulmonary embolism

Hemoptysis (+1.0)

Coughing up blood or blood-streaked sputum

Malignancy with Active Treatment (≤ 6 Months) or Palliative (+1.0)

Active chemotherapy, radiation, surgery, or palliative care for cancer

Diagnostic Workup Pathway (Two-Tier Model)

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.

High-Yield Board Takeaway:

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 $ ightarrow$ 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 $ ightarrow$ treat immediately with LMWH (Enoxaparin) without ionizing radiation.

ENDOCRINOLOGY / NEPHROLOGY DKA & HHS Electrolyte Management

Corrected Sodium in Hyperglycemia

Corrects measured serum sodium for osmotic water shift into the vascular space during severe hyperglycemia (DKA and HHS).

140.0 mEq/L

Eunatremic (Normal)

Measured Serum Sodium (mEq/L)

Normal reference: 135–145 mEq/L

Measured Blood Glucose (mg/dL)

Baseline reference: 100 mg/dL

Katz Formula (Standard Board Formula)

Na + 0.016 × (Glucose - 100)

140.0 mEq/L

Hillier Modern Formula (Glucose > 400)

Na + 0.024 × (Glucose - 100)

144.0 mEq/L

DKA / HHS IV Fluid Selection Rule

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.

Mechanism & High-Yield Board Trap:

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!

NEPHROLOGY / ACUTE KIDNEY INJURY Prerenal Azotemia vs Intrinsic ATN

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.

0.52%

Prerenal Azotemia (< 1%)

Serum Na (mEq/L)

Urine Na (mEq/L)

Serum Cr (mg/dL)

Urine Cr (mg/dL)

Patient On Diuretics? Calculate FEᵘᵣᵙᵃ (Fractional Excretion of Urea)

28.5% (Prerenal)

Serum BUN (mg/dL)

Urine Urea Nitrogen (mg/dL)

Laboratory Diagnostic Interpretation

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 Renal Failure (ATN)
FEₙₐ (Fractional Excretion Na)	< 1%	> 2%
FEᵘᵣᵙᵃ (If on Diuretics)	< 35%	> 50%
Urine Sodium (Uₙₐ)	< 20 mEq/L	> 40 mEq/L
BUN / Serum Creatinine Ratio	> 20:1	< 15:1
Urine Osmolality	> 500 mOsm/kg (concentrated)	< 350 mOsm/kg (isosthenuric)
Urine Sediment Microscopy	Hyaline casts, bland sediment	Muddy brown granular casts, renal tubular cells