Nunc polypropylene cryotubes

Background data were collected by a self-administered validated questionnaire [24 (link)]. The questions included the occurrence of respiratory symptoms, the habits of smoking and tobacco snuffing and information on current and previous diseases. Ten mL of whole blood was collected for determination of pneumoproteins, CRP and biomarkers of smoking and snuffing from the cubital vein in vacutainers without additives (Becton Dickinson and Company, Franklin Lakes, NJ, USA). The samples were centrifuged at 2000 g for 15 min after resting for 45 min. The serum was then pipetted into two 4.0-mL NUNC^® polypropylene cryotubes (Thermo Fisher Scientific, Watham, MA, USA) and frozen immediately at −20 °C before long-term storage at −80 °C at the National Institute of Occupational Health (Oslo, Norway). Blood could not be collected at baseline for one referent.

Venous blood samples (10 mL) were collected in vacuum tubes without additives (Becton Dickinson and Company, Franklin Lakes, NJ, USA) and coagulated for 45 min before centrifugation (2000 g for 15 min). Serum was aliquoted into 4.0 mL NUNC^® polypropylene cryotubes (Thermo Fisher Scientific, Waltham, MA, USA), and thereafter frozen before long-term storage at -80 °C at the National Institute of Occupational Health (Oslo, Norway).

In order to control for smoking status and and for potential differences in smoking habits offshore and at home, nicotine and cotinine in serum were measured among the participants in Part 1 of the study. Blood samples were collected from the cubital vein with 10 mL BD Vacutainers without additives (Becton, Dickinson and Company, Franklin Lakes, NJ, USA). Serum was separated by centrifugation at 2000g for 15 min and pipetted into 4.0 mL NUNC^® polypropylene cryotubes (Thermo Fisher Scientific, Watham, MA, USA). The samples were kept frozen at − 20 °C, until its long-term storage at − 80 °C at the National Institute of Occupational Health. Sample preparation and measurements have been described in detail (Ellingsen et al. 2006 (link)). However, in this study, a different internal standard (cotinine-(methyl-d₃)) was used to improve the within- and between-assay precisions of the analytical method. The detection limits (DL) were 7.3 ng nicotine/mL and 1.7 ng cotinine/mL. The DL was defined as 3 × standard deviation of the blanks.