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.