All participants participating in 1A Visit 2 and 2A Visit 2 handed in urine samples that they collected themselves in a urine container.
A subset of urine samples were immediately used for standard urinalysis to assess concentrations of proteins.
The remaining samples were placed into long term storage for future analyses.

Depending on the participant, one of the following urine samples were collected:

• 24-hour urine samples are considered the gold standard for defining conditions like albuminuria (Gansevoort RT et al. 2006) and has been the standard of care for assessing kidney function, providing a wide range of reference values. 24-h urine samples were collected by adult (18+) participants in a special container over a full 24-hour period.
• An early morning spot (EMS) urine sample was handed in by the first 60.000 adult participants of assessment 1A, but this practice was discontinued due to inconvenience. Participants emptied their bladder before lying down to sleep, did not urinate during the night, and collected one to two ounces of their first urine from the first urination in the morning in a clean container. First morning urine is the most concentrated and the most likely to detect abnormalities of all urine samples.
• A timed overnight (TO) urine sample was collected from underage participants (8-17y). Urine was collected during a 12-hour period, starting from 8pm the night before until 8am of the morning of the Lifelines visit.
  

Participants keep their urine sample at room temperature in urine containers (BD Vacutainer Urine Container 24H 3L -364982) and are instructed to return it to Lifelines within 24 hours after collection is completed.
At the Lifelines location, the container is put in a non‐chilled transport box. The temperature in these boxes is measured by a logtag (Logtag TRIX-8) as soon as the first container is put in the box. The urine boxes are send to the Lifelines laboratory between 9.45am and 11am, where they arrive between 10.30am and 11.30am.

The measuring of the temperature stops at the laboratory.
The results of every logtag is reviewed and particularities are registered in a LIMS.
The maximum temperature during the transport is noted and linked to every sample in a given box.
The urine containers are processed at room temperature.
The weight of every container is registered with a KERN 440.
The vacutainer (BD Vacutainer Urine tube 10ml – 364918) is filled within an hour after receiving the container and is put on the pipetting robot (Synchron Urine Aliquoting Robot – custom build) within two hours after filling it.
All urine samples are aliquotted in 900ųl fractions.
The aliquots are removed from the deck and kept at 4°C, until they can be placed in a ‐80°C freezer ( Sanyo – MDF U74V), before 5.30pm.
The SPREC code is registered with all aliquots based on the real‐time process.

Lifelines samples are stored under controlled circumstances (e.g. ‐80°C and low humidity) in an automatic storage system from Hamilton, called the BIOS XL.
Sample picking is performed by the BIOS in a controlled environment of -20°C with a speed of at least 300 samples a day.
Samples are picked based on 2D barcodes on the bottom of the tubes. Two checks are made:

1. scanning of the tubes in the BIOS
2. outside the BIOS, at max 15°C and in low humidity. This will take max. 5 min.

After picking, samples are stored in -80°C freezer just upon transportation.
Transportation will take place on dry ice with a turn-around-time between removal of the sample out of the freezer and reception on the location of analysis of max 1h.

Samples will be defrosted at room temperature and analysis will take place when defrosting is 100%, within 4 hours after arrival.
Samples will be analysed as described in the manual of the COBAS analyzer.