A 65-year-old man is brought to the emergency department from his home. He is unresponsive. His son requested a wellness check because he had not heard from his father in 2 weeks. He reports that his father was sounding depressed during a telephone call. The paramedics found a suicide note and a half-empty bottle of antifreeze near the patient. The medical history includes hypertension and hyperlipidemia. The vital signs include: blood pressure 120/80 mm Hg, respiratory rate 25/min, heart rate 95/min, and temperature 37.0°C (98.5°F). He is admitted to the hospital. What do you expect the blood gas analysis to show?

Non-anion gap metabolic acidosis

A 36-year-old male is taken to the emergency room after jumping from a building. Bilateral fractures to the femur were stabilized at the scene by emergency medical technicians. The patient is lucid upon questioning and his vitals are stable. Pain only at his hips was elicited. Cervical exam was not performed. What is the best imaging study for this patient?

Computed tomography (CT) scan of cervical spine, hips, and lumbar area

AP and lateral radiographs of hips

Lateral radiograph (x-ray) of hips

Magnetic resonance imaging (MRI) of hips, knees, lumbar, and cervical area

Anterior-posterior (AP) and lateral radiographs of hips, knees, lumbar, and cervical area

A 58-year-old man presents to the emergency department with a chief complaint of ringing in his ears that started several hours previously that has progressed to confusion. The patient denies any history of medical problems except for bilateral knee arthritis. He was recently seen by an orthopedic surgeon to evaluate his bilateral knee arthritis but has opted to not undergo knee replacement and prefers medical management. His wife noted that prior to them going on a hike today, he seemed confused and not himself. They decided to stay home, and roughly 14 hours later, he was no longer making any sense. Physical exam is notable for a confused man. The patient's vitals are being performed and his labs are being drawn. Which of the following is most likely to be seen on blood gas analysis?

pH: 7.30, PaCO2: 15 mmHg, HCO3-: 16 mEq/L

pH: 7.37, PaCO2: 41 mmHg, HCO3-: 12 mEq/L

pH: 7.41, PaCO2: 65 mmHg, HCO3-: 34 mEq/L

pH: 7.47, PaCO2: 11 mmHg, HCO3-: 24 mEq/L

pH: 7.31, PaCO2: 31 mmHg, HCO3-: 15 mEq/L

A mother presents to the family physician with her 16-year-old son. She explains, "There's something wrong with him doc. His grades are getting worse, he's cutting class, he's gaining weight, and his eyes are often bloodshot." Upon interviewing the patient apart from his mother, he seems withdrawn and angry at times when probed about his social history. The patient denies abuse and sexual history. What initial test should be sent to rule out the most likely culprit of this patient's behavior?

Sexually transmitted infection (STI) testing

An investigator is studying muscle tissue in high-performance athletes. He obtains blood samples from athletes before and after a workout session consisting of short, fast sprints. Which of the following findings is most likely upon evaluation of blood obtained after the workout session?

Decreased concentration of NADH

Decreased concentration of lactate

Increased concentration of insulin

A 27-year-old soldier is brought to the emergency department of a military hospital 20 minutes after being involved in a motor vehicle accident during a training exercise. He was an unrestrained passenger. On arrival, he has shortness of breath and chest pain. He appears pale and anxious. His temperature is 37°C (98.6°F), pulse is 110/min, respirations are 20/min, and blood pressure is 100/65 mm Hg. He is alert and oriented to person, place, and time. Examination shows pale conjunctivae and mucous membranes. There is bruising on the chest, extremities, and abdomen. The lungs are clear to auscultation. He has normal heart sounds and flat neck veins. The abdomen is flat, soft, and mildly tender. The remainder of the physical examination shows no abnormalities. High-flow oxygen is applied, and intravenous fluid resuscitation is begun. A chest x-ray is obtained. Which of the following is the most appropriate next step in management?

CT scan of the chest with contrast

Intubation with positive pressure ventilation

A trauma 'huddle' is called. Morphine is administered for pain. Low-flow oxygen is begun. A traumatic diaphragmatic rupture is suspected. Infusion of 0.9% saline is begun. Which of the following is the most appropriate next step in management?

CT of the chest, abdomen, and pelvis

Initial diagnostic workup approach for USMLE Step 2 CK: High-Yield CCS Cases Lessons

Initial Workup - The Diagnostic Game Plan

Strategy: Move from simple, non-invasive, and cheap to complex, invasive, and expensive.
Goal: Rule out common/life-threatening conditions first.

Always treat the patient, not just the lab report.

⭐ In a trauma setting (ATLS), the initial workup often includes a FAST scan, chest X-ray, and pelvic X-ray alongside primary survey and resuscitation.

System Panels - Your First-Line Arsenal

Complete Blood Count (CBC): Your baseline for almost every case.
- Hb: Anemia/Polycythemia
- TLC/DLC: Infection (↑Neutrophils), Allergy (↑Eosinophils)
- Platelets: Bleeding risk
Renal & Liver Function Tests (RFT/LFT): The metabolic dashboard.
- RFT/KFT: Urea, Creatinine, Na⁺, K⁺. Crucial for AKI, dehydration, and electrolyte imbalance.
- LFT: AST, ALT, ALP, Bilirubin. Screens for hepatocellular vs. cholestatic injury.
Coagulation Screen: Essential pre-procedure or in bleeding patients.
- PT/INR (Extrinsic pathway)
- aPTT (Intrinsic pathway)

⭐ In liver function tests, an AST/ALT ratio > 2:1 is highly suggestive of alcoholic hepatitis, especially with an elevated Gamma-Glutamyl Transferase (GGT). This is known as the De Ritis ratio.

Reading the Signs - Interpreting First Results

Baseline is Key: Always compare current results to the patient's previous values if available. A change is often more significant than a single abnormal reading.
Clinical Correlation: Never interpret labs in isolation. Results must align with the patient's history and examination findings.
Pattern Recognition: Look for patterns, not just single abnormal values (e.g., cholestatic vs. hepatocellular LFT pattern).
Critical Values: Labs have defined critical thresholds requiring immediate physician notification and action.

⭐ In metabolic acidosis, always calculate the anion gap to narrow down causes. A high anion gap (> 12 mEq/L) suggests MUDPILES, while a normal gap points to HARDUPS.

Formula: Anion Gap = $Na⁺ - (Cl⁻ + HCO₃⁻)$

High‑Yield Points - ⚡ Biggest Takeaways

Always start with bedside tests: ECG, RBS, and pulse oximetry are crucial first steps.

Prioritize non-invasive tests (like ultrasound) over invasive ones (like biopsy) in the initial phase.

Core labs include CBC, KFT, LFT, and electrolytes; order them early.

Initial imaging, like a Chest X-ray or FAST scan, should be guided by the chief complaint.

Stabilize the patient first (ABC) before any comprehensive diagnostic workup.

Focus on tests that address the most probable and life-threatening diagnoses immediately.

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