National Health and Nutrition Examination Survey

Accurate measurement of blood pressure (BP) is a major public health concern; it is essential for hypertension screening, as well as for disease management. Hypertension is a powerful, consistent and independent risk factor for cardiovascular disease and renal disease.

Heart rate is measured on all children 0-7 years of age; radial pulse is measured on examinees 8 years and older; and blood pressure (BP) is measured on all examinees 8 years and older.

Exclusion criteria: presence of the following on both arms: rashes, gauze dressings, casts, edema, paralysis, tubes, open sores or wounds, withered arms, a-v shunts, or if blood has been drawn from arm within the last week.

After resting quietly in a sitting position for 5 minutes and determining the maximum inflation level (MIL), three consecutive blood pressure readings are obtained. If a blood pressure measurement is interrupted or incomplete, a fourth attempt may be made. All BP determinations (systolic and diastolic) are taken in the Mobile Examination Center (MEC).

The BP examiners are certified for blood pressure measurement through a training program from Shared Care Research and Education Consulting. Certification is achieved when physician examiners meet all requirements of the training program. The initial training includes:

• didactic instruction about BP measurement and propensity for error;
• practice listening to systolic and diastolic BP sounds using a standardized audio-video tape presentation;
• audio-video tape test;
• written exam;
• examiner and gold standard instructor simultaneously listening to BP of a minimum of 20 volunteers of all ages through a Y- stethoscope to compare measures; and
• observation of protocol technique using a checklist.

Certification requires a score of 100 per cent on the audio-video tape test. Correct answers on the audio-video tape test require the examiner’s answers and the standardized test answers to be within +/- 2mm mercury (Hg) on 92 per cent of 24 measures (12 systolic, 12 diastolic), and within +/- 4mm Hg on 100 percent of 24 measures (12 systolic, 12 diastolic). For more information on quality assurance and control, see Ostchega et al. (Ostchega, 2003).

For more details on the QA/QC process for this component, please refer to the Physician Section of the MEC Operations Manual. 

The following specifications were programmed in the computer system used to capture the blood pressure data:

• systolic blood pressure and maximum inflation level cannot be greater than 300 mmHg;
• systolic and diastolic blood pressure and maximum inflation level can be even numbers only;
• systolic blood pressure must be greater than diastolic blood pressure;
• if there is no systolic blood pressure, there can be no diastolic blood pressure;
• diastolic blood pressure can be zero

Please refer to the Analytic Guidelines for further details on the use of sample weights and other analytic issues. The Analytic Guidelines are available on the NHANES website.