Biological specimen collection is an integral part of many longitudinal epidemiological studies. It is important to achieve high participant satisfaction for continuing involvement, and high sample quality for accurate biomarker measurement. We conducted a study to evaluate these issues on the sample collection proposed for the Canadian Longitudinal Study on Aging (CLSA). There were 85 participants recruited, and 65 attended either a hospital laboratory or private laboratory. Approximately 100 mL of blood and a random urine specimen were collected from each participant for a total of 2,108 sample aliquots. Quality standards were met for more than 90 per cent of samples and were similar for samples collected in both laboratories. More than 90 per cent of participants rated satisfaction with the collection as being good or excellent, and 84 per cent would be willing to repeat the collection in one to three years.

Hyperuricaemia is one of the components of metabolic syndrome. Both oxidative stress and hyperinsulinism are important variables in the genesis of this syndrome and have a close association with uric acid (UA). We evaluated the effect of an oral glucose challenge on UA concentrations. The study included 656 persons aged 18 to 65 years. Glycaemia, insulin, UA and plasma proteins were measured at baseline and 120 min after an oral glucose tolerance test (OGTT). The baseline sample also included measurements of total cholesterol, triacylglycerol (TAG) and HDL-cholesterol. Insulin resistance was calculated with the homeostasis model assessment. UA levels were significantly lower after the OGTT (281·93 (sd 92·19) v. 267·48 (sd 90·40) μmol/l; P < 0·0001). Subjects with a drop in UA concentrations >40·86 μmol/l (>75th percentile) had higher plasma TAG levels (P = 0·0001), baseline insulin (P = 0·02) and greater insulin resistance (P = 0·034). Women with a difference in plasma concentrations of UA above the 75th percentile had higher baseline insulin levels (P = 0·019), concentration of plasma TAG (P = 0·0001) and a greater insulin resistance index (P = 0·029), whereas the only significant difference in men was the level of TAG. Multiple regression analysis showed that the basal TAG levels, insulin at 120 min, glycaemia at 120 min and waist:hip ratio significantly predicted the variance in the UA difference (r2 0·077). Levels of UA were significantly lower after the OGTT and the individuals with the greatest decrease in UA levels are those who have greater insulin resistance and higher TAG levels.