Urine test strips and iodine contamination: a tricky trick in iodine nutrition surveys

Abstract

Objective

A recent report from the Faroe Islands suggested mild iodine deficiency among women aged 40 years and older. New preliminary results showed an average urinary iodine concentration of 457 µg/L. This spurious finding encouraged the present report.

Methods

A subset of 17 consecutive pregnant women from an ongoing study provided an additional morning spot urine sample; one part was tested for a few seconds with a test strip for glucose, protein, and erythrocytes, and the other was left untouched. The women recorded the previous week’s intake of iodine-rich foods. Additionally, 12 tap water samples were collected such that three samples were sealed immediately, the remaining were strip tested for 10, 30 and 60 s, respectively. Urine and water samples were analysed using the ceri/arsen method after alkaline ashing.

Results

Median urinary iodine concentration (UIC) in pristine urine samples was 116 µg/L (IQR 79–204 µg/L; range 26–475 µg/L), and positively associated with iodine-rich food intake. UIC increase with test-strip dip varied from 10 to 94 times the non-dip value. In tap water, the pristine samples had an iodine concentration of 2–4 µg/L, which increased to 10,000 µg/L after 60 s.

Conclusion

Urine samples exposed to test strips can be contaminated within a few seconds leading to unreliable iodine results. Therefore, it is crucial that the study protocol clearly states the procedure for urine sample collection and handling, strict adherence to protocol, and that utensils used are dedicated to collecting urine to measure iodine.

Keywords:

• Iodine
• urine
• analysis
• equipment contamination
• pregnant women

Acknowledgement

Special thanks to Marita Hansen and Jóhanna Petursdóttir from the Department of Occupational Medicine and Public Health for helping and organising pregnant women to provide an additional urine sample for the task presented in this article.

Disclosure statement

There are no conflicts of interest.

Additional information

Funding

The work was supported by Aalborg Hospital (S. A. Grant no. 3118) Dancea Research Programme, The Danish Environmental Protection Agency, Grant no. 112-00292. Aalborg Universitetshospital.