br Corresponding author at Department of Epidemiology The
Corresponding author at: Department of Epidemiology, The University of Texas MD Anderson Cancer Center, 1155 Pressler Street, Houston, TX 77030, USA. E-mail address: [email protected] (H. Zhao).
Median levels of CRP by demographics and health behaviors among MAC study participants.
Characteristics N = 2753 (%) CRP, median (range) P-value* CRP, median (range) P-value* CRP, median (range) P-value*
P for trend
< High school
P for trend
P for trend
P for trend
P for trend
*Nonparametric Wilcoxon rank-sum test was applied.
2. Materials and methods
2.1. Study population
The study subjects were drawn from a large population-based on-going prospective cohort of Mexican–American households initiated in 2001 by the Department of Epidemiology at the University of Texas MD Anderson Cancer Center, called the Mano-a-Mano Mexican American Cohort Study (MACS). To be eligible to participate in the MACS, par-ticipants had to self-identify as Mexican or Mexican–American. A de-tailed description of the recruitment strategy and the data collection procedures have been described previously . Briefly, participants have been recruited through block walking through U 46619 centers and local health clinics in predominantly Mexican-American neigh-borhoods in Houston, Texas, and by networking through currently en-rolled participants. Eighty eight percent of the identified eligible households agreed to participate in the study, and written informed
consent was obtained from each participants. After that, trained bilin-gual research interviewers conducted a structured face-to-face inter-view using the participant’s preferred language, either Spanish or English. A standardized and validated questionnaire was used in the interview, which included information on basic socio-demographic characteristics, residential history, lifestyle behaviors, physical activity, personal medical history, family history of chronic disease, accultura-tion, and occupational exposure. Physical activity were measured using
1) survey instruments from the 2007–2008 National Health and Nu-trition Examination Survey (NHANES; CDCP, 2007) and supplemental items following the NHANES format that inquire about activities per-formed in and around the home. Anthropometric measures, including height, weight, and blood pressure, were obtained during the interview. Participants have been followed up via annual telephone re-contact to update BMI, selected exposures, and new diagnosis of selected chronic diseases, including cancer, type-2 diabetes, and hypertension. A total of 2800 participants were selected from CRP measurement. The main
selection criteria included the availability of serum samples, the com-pleteness of questionnaire data, and no existing cancer at baseline. After initial quality check, we excluded 47 participants due to low quality in CRP measurement. Thus, serum CRP data were available for 2753 participants and they were included in the current study. Among them, 177 cancer cases were identified during the follow-up, and further confirmed with the Texas Cancer Registry. The study protocol was approved by the Institutional Review Board of the University of Texas MD Anderson Cancer Center.
2.2. Quantification of CRP level by ELISA assay
Blood draws were completed by trained interviewers. Forty ml of venous blood was collected per participant and stored in barcoded, pre-labeled vacutainers (two 10 ml lavender tops, two 10 ml red tops). Once the blood is drawn, the tubes were inverted several times to completely dissolve their contents. The mixed tubes were then cooled to 4 °C by placing them in an ice bucket to transport to the MD Anderson la-boratory. Serum, plasma and buffy coat were separated within 1 h of collection by centrifuging for 15 min at 2500 rpm. The biospecimens were stored in −80 °C freezer. Quantification of CRP level in serum was performed using the Human C-Reactive protein Quantikine ELISA (R&D systems) according to the manufacturer's instruction. All samples were analyzed in duplicate. A standard curve was created after the duplicate readings for each standard. Negative control, standards, positive con-trol were included in each assay. The absorbance was measured at 450 nm using a microplate reader. Readings at 540 nm were subtracted from the readings at 450 nm, to correct for optical imperfections in the plate. Then CRP concentrations of samples were calculated from stan-dard curve. Any result with an intra assay % CV > 20% were re-analyzed. The intra assay variance ranged from < 5% to 15%.
2.3. Statistical analysis