National Health and Nutrition Examination Survey

The Creatine Kinase questionnaire (variable name prefix CKQ; questions CKQ010 CKD070) collects survey participant interview data to help interpret NHANES laboratory data for serum Creatine Phosphokinase (CPK). CPK is a key enzyme involved in cellular-level energy metabolism (McLeish and Kenyon, 2005). It is in general clinical use as a biomarker for muscle tissue injury.

CPK levels in the serum may be elevated in a number of health conditions, including muscle degeneration, muscle inflammation, certain endocrine disorders, and as a side effect of prescription medications, such as the “statins” (Wu et al., 2009). However, CPK may also be elevated simply as a result of direct injury to muscle or as a result of recent strenuous physical activity (Clarkson et al., 2006).

The main purpose of the CKQ questionnaire was to collect data on factors which may cause transient elevations in CPK (a history of recent injury or heavy physical exertion) so that data analysts can account for such cases in their analyses of the relationship of CPK to health conditions. Also, a single question was asked about a personal history of muscle pain not due to physical exertion or injury, which can occur in instances such as chronic muscle inflammation (myositis). If this was present, the duration of the muscle pain was recorded.

In the 2011-2012 survey, the CKQ was administered to a full sample of NHANES examined participants 12+ years of age as part of the health examination.

These questions were asked, in the NHANES Mobile Examination Center (MEC), by trained interviewers using the Computer-Assisted Personal Interviewing (CAPI) system.

The CAPI system is programmed with built-in consistency checks to reduce data entry errors. CAPI also uses online help screens to assist interviewers in defining key terms used in the questionnaire. During the data collection cycle, periodic QC checks were performed on the questionnaire data being collected and interviewer specific feedback and retraining was performed as appropriate.

A subject's questionnaire interview responses were electronically captured and then uploaded into a computerized database.The data was then edited for completeness, consistency, and illogical values.

The CKQ recall period for whether a participant had a history of a muscle injury or heavy physiclal exertion was the three-day period immediately preceeding NHANES phlebotomy. CKQ also collected data on whether the injury or physical exertion caused symptoms of muscle pain.

Because the CKQ was administered in the NHANES Mobile Examination Center, 2-year MEC examination sample weights should be used when the data is analyzed.

Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for further details on the use of sample weights and other analytic issues.