Timing of blood extraction in epidemiologic and proteomic studies: results and proposals from the PANKRAS II Study.

There are no consensus guidelines or standards for epidemiologic and '-omics' studies using blood biomarkers on how to report the timing of extraction of blood samples. However, disease-induced changes in blood concentrations of exogenous and endogenous compounds may bias studies. The aim of the present report is to describe the timing of blood collection with respect to a variety of relevant clinical events in the PANKRAS II Study, and to suggest ways to display graphically the quantitative information. Subjects were 167 incident cases of exocrine pancreatic cancer prospectively recruited in five teaching hospitals in eastern Spain. Over 80% of patients had blood extracted during the first 6 months since onset of cancer symptoms, and 82% within the first month of admission to a study hospital. Over 80% of cases had blood drawn after an ultrasound, a CT scan or an ERCP, 25% after a laparotomy, and 37% after treatment onset. All three intervals from blood extraction to diagnosis, to treatment onset and to interview had a median of 0 days, and 88% of cases had blood drawn within 2 weeks of diagnosis. Over 72% of cases had concentrations of total lipids in the medium, normal range. Results suggest ways to report intervals involving blood biomarkers and may contribute to develop consensus guidelines and standards on the collection of blood samples in epidemiologic and '-omics' research.