Participants were instructed to collect their urine on the day before their blood was due to be drawn as this provides the possibility to correlate the results between the blood- and urine diagnostic tests. To facilitate urine collection each participant is provided with a BD Vacutainer® 3-liter urine collection container (or equivalent).

Please note that the text below describes the procedures as they are employed during the ongoing third assessment. The baseline- and second assessments differ in various ways, and Lifelines recommends consulting their respective wiki pages to learn more about the procedures employed at those times.

Adult participants were instructed to collect their urine over a full 24-hour period (22:00-22:00) as these samples are considered the “gold standard” to determine conditions such as albuminuria (Gansevoort RT et al. 2006¹⁾) and assessing kidney function.
Underage participants (ages 8–17) were instructed to collect their urine over a 12-hour period (20:00-08:00) because of the inconvenience posed by the 3-liter containers.
Participants were instructed to store their containers at room temperature during the sample collection procedure.

Participants are instructed to take the urine container with them to their second appointment when their blood is due to be drawn. Lifelines places the containers in a non-chilled transport box. The temperatures in these boxes are continuously monitored (LogTag TRIX-8) as part of our quality control procedures. These transport boxes are then shipped to the Lifelines laboratory, typically arriving between the hours of 10:00–12:00.

Upon arrival at the Lifelines laboratory the urine containers are weighed (which is registered in our laboratory information management system) and subsequently used to fill two sample tubes for further processing:

• BD Vacutainer® 6.0 mL Z (No Additive) Plus Urine Tubes, these are sent onwards to the UMCG in a chilled transport box after adding their numbers together.
• BD Vacutainer® 11.0 mL Z (No Additive) Plus Urine Tubes

Urine samples are divided into 900 μl fractions by the Synchron Xperimate robot, a modular robotic pipetting platform. These aliquots can be identified by a unique 2D barcode printed on the bottom of the tubes, and are held within a 1D barcoded rack (LVL technologies Safe® 96 IT or equivalent). The exact location of each individual sample is logged and continuously tracked in our LIMS.

Aliquots are kept refrigerated (at 4 degrees celsius) until they can be moved into a cryofreezer (-80 degrees Celsius), which is typically within 10 hours after sample collection.