OBJECTIVES: To describe the referral behaviors of primary care physicians (PCPs) and specialists in the United States (US) when encountering patients with undiagnosed symptoms.

METHODS: In this cross-sectional study, conducted in January 2023, PCPs and specialists were recruited in the US via physician panels. They were asked to complete an online questionnaire.

RESULTS: Participants included 209 PCPs and 473 specialists: pediatrics (66), cardiology (58), ophthalmology (49), obstetrics/gynecology (47), dermatology (43), neurology (39), gastroenterology/hepatology (35), rheumatology (30), hematology/oncology (28), endocrinology/diabetology (27), urology (19), infectious diseases (17), and nephrology (15). When physicians encountered symptoms, they could not diagnose, 23.0% of PCPs and 26.6% of specialists (range: 8.5% Obs/Gyn, 48.7% neurologists) often suspected a rare disease. Physicians referred patients to another specialist after the initial visit (13.9% overall, 9.6% PCPs, 15.9% specialists [range: 7.4% endocrinologists, 31.6% urologists]), second visit (42.5% overall, 45.5% PCPs, 41.2% specialists), or third or later visit (43.5% overall, 45.0% PCPs, 42.9% specialists). Waiting for (or inconclusive) test results formed the primary reason for delaying referral until the second visit or later: 53.8% overall, 49.7% of PCPs, and 55.8% of specialists (range: 41.7% nephrologists, 72.0% endocrinologists), followed by the long waiting lists for an appointment with another physician (15.3% overall, 15.9% PCPs, 15.1% specialists), and a preference to wait and watch (10.4% overall, 10.1% PCPs, 10.6% specialists). Secondary reasons included the desire of the patient not to see another physician (30.7% overall, PCPs: 36.0%; specialists: 28.1%; p=0.054), insurance/ability to pay for visiting another physician (22.0% overall, PCPs: 23.3%; specialists: 21.4%; p=0.6), and not wanting to interfere with another physician (10.1% overall, PCPs: 5.3%; specialists: 12.3%; p=0.008).

CONCLUSIONS: Differences in referral behaviors exist among PCPs and specialists and within specialties, referral delays were observed for both PCPs and specialists for almost the same reasons. Optimizing referral procedures enhance patient care.