Appendix M - Spot urine methodology NI Report NDNS 2019-2023
Source: data.gov.uk (2025-10-10)

National Diet and Nutrition Survey 2017 to 2023 Report for Northern Ireland. This report presents results from 2017-2023 of the National Diet and Nutrition Survey (NDNS) for Northern Ireland. NDNS is a continuous cross-sectional survey, designed to assess the diet, nutrient intake and nutritional status of the general population aged 18 months and over living in private households in the UK.

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
 
 
 
 
Appendix M  
The spot urine sample: collection and 
processing for urinary iodine 
measurement 
 
M.1 Introduction 
This appendix provides an overview of the spot (single) urine sample collection and 
processing methodology for 2019 to 2023 (years 12 to 15). The COVID-19 pandemic 
necessitated some changes to the protocol throughout the fieldwork period as outlined 
below. 
 
Spot urine samples were collected from participants aged 4 years and over during or following 
a face-to-face visit, for measurement of urinary iodine concentration in order to estimate 
population iodine status. 
 
Iodine concentration in a single spot urine sample contributes to an estimate of population 
median concentration and is used to estimate population iodine status by comparison against 
population thresholds defined by the World Health Organization (WHO, 2007). It does not 
provide information about an individual’s iodine status because iodine concentration fluctuates 
widely depending on urine volume, dilution, recent iodine intake and other metabolic and 
physiological factors. As such, the proportion of the population with insufficient iodine intake 
cannot be determined from this data. 
An overview of the methods of analysis and the associated quality control and quality 
assessment procedures for urinary iodine measurement are provided in appendix Q. 
 
M.2 Consent 
Eligible participants aged 16 years and over were asked to give written consent. For children 
aged under 16 years, written consent was sought from a parent or legal guardian, with written 
assent from the child participant where possible. 
 
Information leaflets were provided for participants, including an appropriate version for 
children. The most recent versions used during the fieldwork period covered by this report 
are included in appendix C. Any earlier versions, for example, as adapted for use during the 
COVID-19 pandemic, are available on request.    
M.3 Exclusion from participation in providing a spot urine sample 
Participants were asked a series of screening questions to assess their eligibility for providing 
a spot urine sample. Participants aged under 4 years, those using a urinary catheter, and 
those who were incontinent were excluded and not asked to provide a spot urine sample. If 
participants could not provide a sample at the interviewer visit then the interviewer could, at 
their discretion, leave a home collection kit so that they could post back the sample at their 
convenience.  

 National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
 
 
 
Prior to year 12 participants were requested not to provide a urine sample when they were 
menstruating, however this restriction was lifted from year 12 and participants could provide a 
sample if they felt comfortable doing so. 
 
M.4 Changes as a result of the COVID-19 pandemic 
Fieldwork was suspended in March 2020 due to the COVID-19 pandemic. Interviewers were 
able to restart fieldwork in October 2020 with remote fieldwork protocols. The interviewer 
stage used a telephone interview and spot urine samples were not collected. Participants 
who were subsequently visited by a biomedical fieldworker were asked if they were willing to 
provide a spot urine sample, and if so a home collection kit and pre-addressed, pre-paid 
postal package was left with them to complete and post back the sample at their 
convenience. 
 
In April 2021, a flexible approach, whereby face-to-face or telephone interviews could be 
conducted was employed. Where participants were visited face-to-face they were asked to 
provide a spot urine sample (either during the visit or by posting back a home collection kit). If 
their interview was over the telephone then they were asked to provide a sample (using a 
home collection kit) at the biomedical fieldworker visit. Due to the differences in the fieldwork 
mode over the 4 survey years, the gap between dietary data collection and spot urine 
collection was up to 22 months. 
 
M.5 Interviewer training, procedures and instructions 
Information about the recruitment and training of interviewers is provided in appendix B, and 
detailed protocols are included in appendix L. The instructions provided to interviewers were: 
• check the participant’s eligibility for providing a spot urine sample. If the participant 
did not meet the eligibility criteria they were not asked to provide a sample 
• ensure that the participant understood the spot urine collection procedures 
• confirm and obtain the appropriate written consents 
• label the universal tube with the participant’s serial ID, date of birth, sex and 
barcode label 
• ask the participant to pass urine (not from the first urine pass after waking) directly 
into a labelled 30 mL “universal” tube without touching the inside surface with their 
fingers or hands. Participants were also asked to avoid using sources of iodine 
contamination such as antiseptic sprays and wipes 
• record the details of the sample collection in the Computer Assisted Personal 
Interview (CAPI) program 
• leave the £5 spot urine sample gift card with the participant. 
 
Immediately after the visit the interviewers were instructed to send the universal tube 
(encased in rigid outer packaging) to MRC Epidemiology Biorepository in the pre-addressed 
postal pack by first class post at ambient temperature and to post the associated consent 
form to NatCen. 
 
If participants were unable to provide a sample during the interviewer visit, or if they had a 
telephone interview and a biomedical visit, they were offered the option of collecting and 

 National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
 
 
posting their own spot urine sample independently. Where this was the case, the fieldworker 
assigned labels to the tube, respective dispatch note and consent form and collected 
participant’s written consent. They then left the spot urine home leaflet, spot urine kit, the 
dispatch note and a pre-paid envelope with the participant, asking them to post the sample 
within 24 hours (if possible) along with the completed dispatch note. The participant was then 
given a £5 gift card at the end of the visit. 
 
M.6 Sample tracking, reception and storage 
Upon receipt at MRC Epidemiology Biorepository, the samples were imported into a 
laboratory information management system (LIMS) (LabVantage Solutions Limited, High 
Wycombe, UK). Samples were cross-checked in the study database to ensure correct 
labelling and verify identification. Samples were aliquoted and frozen (at –70°C) on the day of 
receipt. 
 
References 
World Health Organization (2007) Assessment of iodine deficiency disorders and monitoring 
their elimination: a guide for programme managers, 3rd ed (who.int)