A simple and versatile method for frequent 24 h blood sample collection in healthy older adults

Repeated 24 h blood sampling, which is required for time series analyses of metabolites and/or hormones that show strong fluctuations in blood concentration over time, has a higher failure rate in older adults. We tailored existing venipuncture protocols toward use for 24 h blood sampling (sampling frequency of 10 min) in older adults. The following modifications were made: • Pre-sampling: evidence based risk assessment of older adults. • During sampling: • Ultrasound-guided identification and characterisation of veins. • Use of 20-gauge arterial catheter with guide wire for venous access. • Measures to prevent and/or reduce unidirectional blood flow (fluid flow into but not out of the vein) included: • Use of hot water bottles to dilate veins. • Use of small gauge syringes, shortening of the extension line, and slowing of the blood withdrawal rate to reduce pressure on veins. • Stimulation of movement of the arm or retraction of the IV cannula to relieve mechanical flow obstruction. • Post-sampling: prevention of bruising and prolonged bleeding.