Laboratory assessments

All laboratory assessments were performed on venous samples taken in the morning after a minimum of 8 hours fast. Venous blood was drawn into 5 different collection tubes, 3mL each, using vacutainers.

Blood testing was carried out by a certified laboratory (Medlab, www.medlab.com.pe) using their qualified personnel to do all sampling procedures and to be in charge of transport of samples to the laboratory’s facilities. Medlab’s fulfilment of laboratory quality control analysis has been made independently by US-based company Bio-Rad (www.biorad.com). The investigators had access to previous Medlab’s quality control evaluations and reports. In brief, quality control procedures involved the supply of samples with exact and known levels, and the Medlab’s measurements on these samples were compared against a reference laboratory. Most laboratory results for Medlab were within a good quality reference range, that is, ± 1 standard deviation and < 1 for the coefficient of variation, a reference range provided by the independent assessment company. (Quality control reports for glucose, HDL, total cholesterol and insulin tests are presented as examples in Appendix F, Laboratory performance overview).

Medlab’s personnel followed a pre-established quality control protocols for health and safety and for management of blood samples for this study (see Appendix G, Field and laboratory processes for blood testing and storage of samples). All study personnel and laboratory personnel were aware of these procedures. This protocol outlined all laboratory tests to be carried on each subject’s blood sample, including the minimum amount of venous blood sampling necessary to secure that enough blood, serum and plasma were available for the assays. Additional carefulness was placed in processing blood samples for the measurement of glucose in plasma by using a separate tube for this specific assay (see Appendix G, page 441).

In Lima, Medlab’s laboratory personnel visited the research clinic and took directly the blood samples. One of Medlab’s personnel travelled with the research team to the rural site and ensured that the same quality control protocol was followed in the rural site. All blood samples, from all participants in both study sites, were sent to the laboratory headquarters within 24 hours of sampling, and tests were conducted as soon as they arrived to the laboratory facilities.

Serum glucose, insulin, CPR, total cholesterol, HDL, and triglyceride levels were measured using a Cobas® Modular Platform automated analyser and reagents supplied by Roche Diagnostics [211]. The same procedure was used to measure LDL in people with triglycerides greater than 400 mg/dL (n=29, 2.9% of all participants studied). In those with triglycerides below 400 mg/dL, LDL was calculated using the Friedewald equation [157, 158]:

In mg/dL: LDL = total cholesterol – HDL – (0.2 × triglycerides) In mmol/L: LDL = total cholesterol – HDL – (0.45 × triglycerides)

HbA1c was measured on fasting whole blood and analysed by High Performance Liquid Chromatography using automated D-10 Bio-Rad haemoglobin analysers [212]. Plasma fibrinogen was measured by coagulometry technique using a Dade-Behring CA-500 analyser.

Laboratory result outputs were available electronically on an intranet site with access to the main investigator through a secured password. An excel spreadsheet with all

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participants laboratory tests and two printed copies of laboratory results were provided to the research team on a regular basis. A copy of the results was later given to the participants and the other copy was archived.

4.1.4. Study organisation and execution 4.1.5. Census update

The main objective of this activity was to identify the sampling frame for the proposed research in the urban area in Lima. This issue is of particular importance since Lima hosts nearly 9 million people, a third of total Peruvian population. It will be impossible to use the whole city of Lima as the primary sampling unit for the sampling process. The specifics of this project, looking at migrant population, also require a focused approach.

Based in previous research undertaken in one of Lima’s shantytowns it was decided to conduct the study in part of the district of San Juan de Miraflores. Asociación Benéfica PRISMA carried out a census of the area called Pampas de San Juan in 1997 with further update in 2000. The settlement in this area started in 1980’s, which coincides with the periodicity of the mass migration observed in Peru detailed in the background section.

Based on information from these censuses in Las Pampas de San Juan de Miraflores, a total 43,891 inhabitants were counted, organised in 37 settlements. Information on place of birth was available for 99.7% of them, and a total of 4,738 people of all ages responded to have been born in Ayacucho.

An updated census was co-ordinated and carried out by the investigator in January and February 2006. Concretely, the specific aim of an updated census was to identify adult people for the rural-urban group, defined as those who were born in and migrated from Ayacucho into Lima, and who were permanently living in the area of study.

After updating records for place of birth, further migration and other factors, a total of 1,264 people aged 25 or more were found. Information about reasons for

migration, e.g. socioeconomic (job or studies) or forced migration (afraid or terrorism) were also obtained. This updated census was used as the primary platform for random selection of individuals for the rural-urban group.

In the case of San Jose de Secce in Ayacucho, a small-scale census was conducted in mid 2007 to identify all adult population permanently living in the area. In this census in the rural area, 398 adults were identified and this was used as the sampling frame for the rural group.