Our Staff

Nizar Ramzan MD, AGAF, CPE
Gastroenterology/Clinical Research

Nizar Ramzan MD, AGAF, CPE is a Board Certified Specialist in Gastroenterology and Internal Medicine. He is a fellow of the American Gastroenterological Association (AGA) and a member of the American College of Gastroenterological (ACG) as well as a Certified Physician Executive (CPE). Dr Ramzan was named "Top Doc" in PHOENIX Magazine and prides himself in continuing education such as Clinical Integration, Healthcare, Quality Improvement in Healthcare and Hepatology. Dr. Ramzan is committed to the highest quality of care for his patients and dedicated to preserving their digestive health.

Dr Ramzan has two speciality components to his practice:

Colon & Digestive Health Specialists (CDHS), is his private practice. Patients receive personalized care for the prevention, diagnosis and management of gastrointestinal disorders; and Digestive Heath Research Unit (DHRU) www.gastrotrials.com is his clinical research trials practice. Patients have an opportunity to participate in Dr Ramzan's ongoing studies to further the research of new treatments.

In his ongoing quest to assist in finding new treatments for patients, Dr Ramzan is committed to the highest quality of care for both his patients at CDHS and participants in his clinical research trials at DHRU.


  • MAYO CLINC, Rochester MN - completed fellowship training in Gastroenterology and Hepatology.
  • MAYO CLINIC, Scottsdale AZ - Consultant and educator in the Division of Gastroenterology, Department of Medicine. His clinical focus was Inflammatory Bowel Diseases and Endoscopy.
  • Colon & Digestive Health Specialists, PC (CDHS) established in 2003, Scottsdale, AZ
  • Arizona Digestive Center (ADC) an OutPatient Ambulatory Center, AAAHC credentialed is located in the adjacent suite to CDHS where traditional GI procedures are performed.


  • Participates in the Research of new medications for Crohn's Disease and Ulcerative Colitis and other GI disorders
  • Lectures in Inflammatory Bowel Diseases
  • Participates in training of medical students
  • Published in peer reviewed medical and research journals

S. Jaffrey Kazi, MD

Dr. S. Jaffrey Kazi is a board certified gastroenterologist who trained at a University of Chicago-affiliated program and specializes in advanced therapeutic endoscopy. He was in private practice in Chicago before moving to Scottsdale AZ in 2004 . He is highly competent in advanced endoscopies such as ERCP and has a special interest in disorders of bile ducts and pancreas. On a day to day basis he performs upper endoscopy (EGD), colonoscopy, PEG tube placements( feeding tubes), hemorrhoidal treatment and push enteroscopy (endoscopy of small intestine). Dr. Kazi is actively involved in various committees at Scottsdale Healthcare Shea and Osborn. He's on the credentialing committee (Osborn) and on the pharmacy and therapeutic committee (Shea). In addition to serving on committees he was the Vice chair of the Department of Medicine at Scottsdale Healthcare-Shea. He also teaches medical students and lectures. He is an assistant professor at Midwestern State University, School of Medicine. He is also involved in teaching medical students and physician residents . Extracurricular interests include reading books, travel and running marathons.


  • Assistant Professor at Midwestern State University.
  • Clinical Instructor for residency program at Osborn Hospital, Scottsdale Arizona.

Clinical Research Division is conducting the following IRB national trials on the treatment of following clinical conditions.

Dr. Kazi is offering Food sensitivities testing and it's management protocol.

Dr. Kazi is offering Hydrogen Breath Test for Small Intestinal Bacterial Overgrowth( SIBO) to detect "good bacteria and bad bacteria in the intestines".

Kelly Kollman, PA-C

Ms. Kollman is a certified Physician Assistant who graduated from Midwestern University, College of Health Sciences, in Glendale, AZ. She did a one year mid-level fellowship in Hepatology at Mayo Clinic in their American Association for the Study of Liver Diseases (AASLD) sponsored training program. After completing her fellowship, she worked as a Transplant Hepatology Physician Assistant at Mayo Clinic for three years prior to joining Colon & Digestive Health Specialists in March 2011. Ms. Kollman is interested in hepatology, metabolic disease, obesity prevention, management and treatment, preventative medicine and nutrition.

Robert Geoffrey Leon, M.D.

Robert Geoffrey Leon, M.D. has been in private practice in the Scottsdale area since 1977. He is board certified in Internal Medicine and Gastroenterology. Dr. Leon attained his medical degree at State University New York Medical Center in Syracuse, NY and interned at Maimonides Medical Center in Brooklyn, NY. He completed Internal Medicine residency at Rochester General Hospital in Rochester, NY and was awarded to serve as Chief Resident for the Department of Medicine at Rochester General Hospital. Dr. Leon has been an instructor to medical students and residents throughout his career as well as project physician teaching nurse clinicians at Arizona State University. Dr. Leon provides comprehensive medical services in gastroenterology with special interest in functional bowel disorders, peptic difficulties and cancer prevention. Dr. Leon has been named as a Phoenix Magazine 'Top Doc' and is on staff at Scottsdale Healthcare-Osborn, Select Specialty Hospital and Arizona Digestive Center.