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 were instructed to keep the urine sample cool and to return it to Lifelines within 24 hours after collection is completed.

All urine samples were aliquotted in 900ųl fractions using the Synchron Urine Aliquoting Robot. Urine samples were processed using two different methods

1. Plain
2. Addition of small amounts (~50ų) of EDTA to acidified solutions of ascorbic acid in deionized water, in order to protect vitamins against copper-catalysed aerobic oxidation.