Ambulatory Health Care Data

Welcome NHAMCS Participants

The National Health Care Surveys (including NAMCS, NHAMCS, and NHCS) are working with the Centers for Medicare and Medicaid Services Electronic Health Record Incentive Programs: Promoting Interoperability (PI) (formerly known as Meaningful Use (MU)) and the Merit-based Incentive Payment System (MIPS). Click here to find out more.


Contact Information

If you have any questions or comments related to participation, please contact Akintunde Akinseye at:

Ambulatory and Hospital Care Statistics Branch
National Center for Health Statistics
3311 Toledo Road
Hyattsville, Maryland 20782
Phone: 800-223-3815
Fax: 301-458-4032

If you have questions about the survey that are not related to participation, please contact:

Ambulatory and Hospital Care Statistics Branch
National Center for Health Statistics
3311 Toledo Road
Hyattsville, Maryland 20782

Contact CDC-INFO


What is NHAMCS?

The National Hospital Ambulatory Medical Care Survey (NHAMCS) is the Nation’s foremost study of ambulatory medical care in hospital emergency and outpatient departments and has been conducted annually since 1992.

Each year, approximately 500 nationally representative hospitals provide data on a sample of patient visits to selected outpatient clinics, emergency service areas, and, since 2009, ambulatory surgery locations. Sample data are collected over a 4-week reporting period which varies by facility. These data are weighted to produce national estimates which are widely used by health care researchers, policy analysts, congressional staff, the news media, and many others to improve our knowledge of medical practice patterns.

Reliable NHAMCS data depend on complete reports from all sampled hospitals. Data from all sample cases are needed to ensure that policy decisions are based on the most accurate data possible.




Who is eligible to participate?

Non-Federal general and short-stay hospitals, located in the 50 States and the District of Columbia, that have a 24-hour ED, an OPD with physician services clinics, or hospital-based ambulatory surgery locations, are eligible for selection in NHAMCS. Participation is voluntary.


Why participate?

Your facility was randomly chosen to provide representative data not only for its own outpatient clinics, emergency service areas, and ambulatory surgery locations, but also for similar hospitals in the same geographic region. By participating in NHAMCS, you help provide a yearly national description of hospital-based ambulatory medical care services in the United States.


What are the benefits of participating?

Your hospital’s participation will result in more reliable statistics and will enable researchers to better measure the utilization and provision of ambulatory health services.  The need for more complete ambulatory medical care data has been accentuated by recent efforts towards health care reform, the rapidly aging population, the growing number of persons without health insurance, emergency department crowding, the introduction of new medical technologies, and the shift from hospital inpatient to outpatient surgery. Failure to participate lessens the accuracy of the data used by researchers.


How does the process work?

Hospitals are chosen for participation through a random selection process. Letters informing hospital administrators about the purpose of the study are sent first. Then, approximately 5 weeks before the hospital’s reporting period, the administrator is contacted by a U.S. Census Bureau field representative (FR) who confirms that the hospital is eligible for participation. Once confirmed as eligible, the FR will conduct an induction interview with hospital staff to determine which clinics will be participating in the study.

During the hospital’s reporting period, the FR abstracts information on patient visits from medical records. NCHS places high priority on protecting patient confidentiality and adhering to the requirements of HIPAA, and all information is collected in a way that protects patient identity. As part of our data quality process, we re-abstract a small percentage of records to check the reliability of our data collection agents. For this reason, we also collect the patient’s medical record number to assist in the record retrieval process.

If you would like more information on participation, please contact Akintunde Akinseye at or (800) 223-3815, or visit our Ambulatory Health Care Data home page.


Confidentiality and Privacy


Confidentiality of NHAMCS data

NCHS is legally bound to assure the confidentiality of all responses, including any information that might result in a physician or hospital being identified. The data files that are released for research do not include any provider or patient identifying information.

We take your privacy very seriously. All information that relates to or describes identifiable characteristics of individuals, a practice, or an establishment will be used only for statistical purposes. NCHS staff, contractors, and agents will not disclose or release responses in identifiable form without the consent of the individual or establishment in accordance with section 308(d) of the Public Health Service Act (42 U.S.C. 242m(d))External and the Confidential Information Protection and Statistical Efficiency Act of 2002 (CIPSEA, Title 5 of Public Law 107-347)External. In accordance with CIPSEA, every NCHS employee, contractor, and agent has taken an oath and is subject to a jail term of up to five years, a fine of up to $250,000, or both if he or she willfully discloses ANY identifiable information about you. In addition, NCHS complies with the Federal Cybersecurity Enhancement Act of 2015 (6 U.S.C. §§ 151 and 151 note). This law requires the federal government to protect federal computer networks by using computer security programs to identify cybersecurity risks like hacking, internet attacks, and other security weaknesses. If information sent through government networks triggers a cyber threat indicator, the information may be intercepted and reviewed for cyber threats by computer network experts working for, or on behalf, of the government.

The Federal Cybersecurity Enhancement Act of 2015 permits monitoring information systems for the purpose of protecting a network from hacking, denial of service attacks and other security vulnerabilities.1 The software used for monitoring may scan information that is transiting, stored on, or processed by the system. If the information triggers a cyber threat indicator, the information may be intercepted and reviewed for cyber threats. The Cybersecurity Act specifies if any information that is scanned by the cybersecurity software programs is found to be suspicious, it may be reviewed for specific threats by computer network experts working for the government (or contractors or agents who have governmental authority to do so). The Act further specifies that such information may only be used for the purpose of protecting information and information systems from cybersecurity risks.

1“Monitor”means”to acquire, identify, or scan, or to possess information that is stored on, processed by, or transiting an information system”; “information system” means “a discrete set of information resources organized for the collection, processing, maintenance, use, sharing, dissemination or disposition of information”; “cyber threat indicator” means “information that is necessary to describe or identify security vulnerabilities of an information system, enable the exploitation of a security vulnerability, or unauthorized remote access or use of an information system”.


HIPAA Privacy Rule and NHAMCS

This section contains an overview of the Privacy Rule and how it affects your NHAMCS participation.  For more comprehensive information on the Privacy Rule and the NHAMCS, please go to HIPAA Privacy Rule Questions and Answers for NHAMCS.

The final Privacy Rule has been published as required by the Health Insurance Portability and Accountability Act of 1996  (HIPAA).  Health care providers who transmit financial and administrative health information electronically must comply with the Rule as of April 14, 2003.

The Privacy Rule permits your facility to make disclosures of protected health information without patient authorization for public health purposes or for research that has been approved by an Institutional Review Board (IRB).  This survey meets both of these criteria. Additionally, disclosures may be made under a data use agreement Cdc-pdf[PDF – 200 KB] with NCHS.  If you have questions about your facility’s rights as a respondent, you may call the IRB at 1-800-223-8118.  The IRB is an independent board that protects the interests of people who take part in studies.  Click here to see the IRB approval letter Cdc-pdf[PDF – 3 MB] for NHAMCS.

We have included all the information you need to be assured that your facility is allowed to disclose protected health information for the NHAMCS in our introductory letters Cdc-pdf[PDF – 176 KB] to hospitals and also here at our website.  However, there are several things that you must do to ensure compliance with the Rule when participating in the survey. First, the privacy notice that your facility generally provides to patients must indicate that patient information maybe disclosed for either research or public health purposes.  And, secondly, your facility may need to keep a record of the disclosure Cdc-pdf[PDF – 17 KB] (which we will provide) that shows that some data from the patient’s medical record were disclosed to CDC for the NHAMCS. Of course, if your facility does not transmit health information electronically (such as claims data), then it is not subject to the Privacy Rule or the requirements described above.

The Privacy Rule applies to data collected for NHAMCS because we are asking you to provide certain information about patients without their authorization.  For public health and research purposes, NHAMCS collects information from the patient’s medical record such as visit date, birth date, and residential ZIP code.  While not directly identifiable, these data are considered protected health information as defined by the Privacy Rule.  As described above, the Rule allows you to disclose this information for public health and research purposes.

Please be assured that we fully intend to continue our long history of gaining the voluntary participation of hospitals like yours by upholding the highest confidentiality standards and practices.

For additional information on the confidentiality of NHAMCS data, please go to NCHS’s Privacy Protection page and “Frequently Asked Questions (FAQ’s)” about the NHAMCS.


Data Utilization


Professional Endorsements

“NHAMCS is an invaluable resource for anyone who wants to understand critical issues about access to care, utilization of hospital emergency departments, and other matters of fundamental importance to the health of Americans.”  — Art Kellermann, MD, MPH, FACEP, Paul O’Neill-Alcoa Chair in Policy Analysis, RAND Corporation; Former Professor and Chairman, Department of Emergency Medicine, Emory School of Medicine

NHAMCS is endorsed by the following professional organizations:

  • American Academy of Ophthalmology
  • American College of Emergency Physicians
  • American College of Osteopathic Emergency Physicians
  • American Health Information Management Association
  • Emergency Nurses Association
  • Society for Academic Emergency Medicine
  • Society for Ambulatory Anesthesia


Data Supplements from Previous Years

The following supplement was used from 2006-2010:

  • Cervical Cancer Screening Supplement Cdc-pdf[PDF – 138 KB]In 2006, CDC’s National Center for Health Statistics and National Center for Chronic Disease Prevention and Health Promotion joined forces to collect information on the screening of cervical cancer at hospital-based outpatient departments in the United States.Genital human papillomavirus (HPV) infection is common among sexually active populations.  At the start of the supplement, there was considerable new information about HPV infection, transmission, and methods of prevention. In addition, a new DNA test to detect HPV as well as newly approved indications for HPV testing were seen as having important implications for clinicians in both their cervical cancer screening practices and their management of positive HPV diagnoses among female patients and their sex partners. There was recognition that this new information might require different approaches to cervical cancer screening in primary care practice, as well as new information that needed to be conveyed when counseling and educating patients and their sex partners.The Cervical Cancer Screening Supplement was a self-administered 4-page questionnaire given to medical directors of general medicine and obstetric-gynecology clinics that performed cervical cancer screening.  The content included questions about screening methods for cervical cancer, including ordering HPV DNA tests, and administration of the HPV vaccine.

The following supplement was used in 2008:

  • Pandemic and Emergency Response Preparedness Supplement Cdc-pdf[PDF – 283 KB]The Pandemic and Emergency Response Preparedness Supplement was added to the 2008 NHAMCS at the request of the Office of the Assistant Secretary for Planning and Evaluation (OASPE) of the Department of Health and Human Services (DHHS). Information was obtained on the content of the hospital’s emergency response plan, staff training, participation in mass casualty drills, and the hospital’s resources and capabilities.The questionnaire was adapted from a previous NHAMCS supplement on Bioterrorism and Mass Casualty Preparedness that was fielded in 2003 and 2004. Certain elements (such as existence of updated emergency response plans) remained the same in order to be able to establish trends over time. Other elements were revised to answer questions generated by the previous surveys and newer public health priorities. Examples include adding infectious diseases such as influenza and severe acute respiratory syndrome (SARS), expanding the categories for chemical and radiological exposures to include specific agents targeted in the hospital preparedness grant guidances, and adding specificity on some resources such as decontamination showers, to include numbers of patients able to be accommodated.The content included questions about evacuation plans and the set-up of temporary facilities should the hospital not be able to operate. Supplement data will be used to assess progress towards hospital preparedness for dealing with bioterrorism and mass casualty incidents, and in so doing evaluate the ability of hospitals to deal with naturally occurring diseases, epidemics and pandemics, such as SARS or influenza. This project supports the DHHS goal to prepare for emerging health threats. The project also provides nationally representative benchmarks that can serve as one quality control mechanism for other projects that are designed to detect emerging health threats within a shorter time period.


The following supplement was used in 2002, 2003, and 2006:

  • Emergency Pediatric Services and Equipment Supplement (EPSES) Cdc-pdf[PDF – 576 KB]The Emergency Pediatric Services and Equipment Supplement (EPSES) was first used in 2002 and 2003 and reintroduced in 2006. It was sponsored by the Health Resources and Services Administration (HRSA) and assessed how well hospitals were prepared to provide emergency pediatric services. NCHS is using the data collected to evaluate emergency pediatric preparedness at a national level. This is NOT an assessment or evaluation of individual hospitals. This is a study to produce data for national statistics on pediatric preparedness in hospital ED settings.


The following four supplements were used in 2003 and 2004.

  • Hospital Capacity Card Cdc-pdf[PDF – 334 KB]Because hospital personnel frequently report that the chief reason for ED crowding is the lack of inpatient beds, it is important to obtain inpatient bed counts.  Comparing the number of licensed and staffed beds on the Hospital Capacity Card will provide an indication of untapped capacity.  NCHS would like to do a comparison of the daily inpatient occupancy rate with the frequency of ambulance diversion.
  • ED Staffing and Capacity and Ambulance Diversion (SCAD) Supplement Cdc-pdf[PDF – 566 KB]The purpose of this supplement is to obtain data on issues related to ED crowding.  It is important to know if the ED performs triage, how many treatment spaces there are, specific information about physician staffing, and the availability of on-all specialists.  NCHS would like to know the training level of physicians working in the ED in order to assess how it accounts for variation across EDs in observed treatment patterns.
  • ESA Ambulance Diversion Log Cdc-pdf[PDF – 1.8 MB]The purpose of the Ambulance Diversion Log is to obtain data on ambulance diversion.  There are no national estimates available on diversion frequency and no information comparing types of cases seen in EDs while they are on diversion.  In order to help policymakers, NCHS would like to know in what proportion of hospitals diversion occurs and with what frequency; the reasons for the diversion; and who in the hospital ordered the diversion.
  • Bioterrorism and Mass Casualty Preparedness Cdc-pdf[PDF – 645 KB]There is a growing appreciation of the unique role of the ED within the US health care system and of its expanding role as a “safety net” provider.  The attacks on September 11, 2001, and the subsequent cases of anthrax spotlight the quintessential role of EDs in the immediate response to mass casualty incidents and in the detection and surveillance of bioterror-related diseases.  To improve their preparedness for biological and chemical attacks, hospitals face clinical and communications challenges.  One of the biggest obstacles to a hospital’s readiness is recognizing the early signs of a terrorism-related condition, because many biochemical agents trigger routine symptoms in patients.  This is a self-administered two-page questionnaire pertaining to the hospital’s preparedness for events involving bioterrorism and mass casualties.  It includes questions on additional training received on this topic since September 11, 2001.
Page last reviewed: October 16, 2018