A 42-year-old male manual laborer presents with a 3-week history of fever, new cardiac murmur, and malaise. On examination, multiple linear hemorrhages are noted under the nails of both hands, running **B** (parallel to the long axis of the nail). Blood cultures are pending. Which of the following is the MOST appropriate next step in the diagnostic workup for suspected infective endocarditis?

Explanation

## Why "Obtain blood cultures from 3 different sites, >1 hour apart, BEFORE starting antibiotics" is right The presence of multiple splinter hemorrhages running parallel to the nail axis, combined with fever and a new cardiac murmur, raises strong suspicion for infective endocarditis (IE). According to Robbins 10e and standard endocarditis diagnostic protocols, blood cultures must be obtained from at least 3 different sites, separated by >1 hour, and BEFORE any antibiotic therapy is initiated. This maximizes the yield of isolating the causative organism and allows for appropriate targeted antimicrobial therapy. The parallel orientation of splinter hemorrhages (structure **B**) is the classic morphologic finding, and when multiple nails are affected in a febrile patient with cardiac findings, endocarditis must be ruled out before attributing them to trauma. ## Why each distractor is wrong - **Start empirical broad-spectrum antibiotics immediately without waiting for culture results**: While empirical antibiotics may be necessary in unstable patients, the standard of care in suspected IE is to obtain blood cultures FIRST. Premature antibiotics reduce culture positivity and compromise diagnosis. Cultures should be drawn before or within the first hour of antibiotic initiation in stable patients. - **Perform chest X-ray to assess for pulmonary septic emboli**: While imaging may be part of the workup, it is NOT the most appropriate FIRST step. Blood cultures and echocardiography are the diagnostic cornerstones of IE diagnosis. Chest X-ray is adjunctive and does not establish the diagnosis. - **Obtain a single blood culture and begin antibiotics within 1 hour**: A single culture is insufficient for IE diagnosis and increases the risk of contamination being mistaken for true bacteremia. The standard requires 3 separate cultures from different sites to establish diagnosis and guide therapy. **High-Yield:** In suspected endocarditis with splinter hemorrhages, ALWAYS obtain 3 blood cultures from different sites >1 hour apart BEFORE antibiotics — this is the diagnostic gold standard and prevents missing the organism. [cite: Robbins 10e Ch 12; Hutchison's Clinical Methods; Duke Criteria for Infective Endocarditis]