Allen Ruan, MD, FAAP. Pediatrics. (303) 938-4750. (303) 938-4753 (Fax) 4745 Arapahoe Ave., Suite 200, Boulder, CO 80303. 1551 Professional Lane, Suite 270, Longmont, CO 80501. Allen Ruan, MD is a board-certified pediatrician. He welcomes new patients to his practice in Boulder and Longmont..