How Urine Test Strips Affect Iodine Nutrition Surveys

Iodine, a vital micronutrient, is crucial for the synthesis of thyroid hormones, which regulate metabolism, growth, and development. Monitoring iodine levels in populations is essential to prevent iodine deficiency disorders (IDD) and excess iodine-induced thyroid dysfunction. Urine tests, particularly measuring urinary iodine concentration (UIC), are the cornerstone of iodine nutrition surveys due to their non-invasive nature and high correlation with dietary iodine intake. However, recent findings from the Faroe Islands have brought to light a significant yet overlooked issue: contamination of urine samples by test strips, leading to inaccurate UIC results.

Fig.1 The ratio (left y-axis) of iodine concentration in urine samples before and after urine test strip (solid line and dotted trend). (Veyhe A. S., et al., 2022)

The Faroe Islands Study: A Wake-Up Call

• Background and Objective
  The Faroe Islands, a North Atlantic archipelago, participated in a comprehensive study aimed at assessing iodine nutrition among pregnant women. Initial reports from this region suggested a mild iodine deficiency, which prompted further investigation into the iodine status of the population. Unexpectedly, preliminary results from stored urine samples indicated excessively high urinary iodine concentration (UIC) levels, far beyond the expected range. This anomaly raised suspicions of potential contamination, which could skew the results and mislead public health interventions. This led to a focused study examining whether urine test strips, commonly used for detecting glucose, protein, and erythrocytes, could be the source of this unexpected contamination.
• Methodology
  The study recruited 17 pregnant women from an ongoing birth cohort in the Faroe Islands, ensuring a representative sample of the population under investigation. Morning spot urine samples were collected from each participant to minimize variability in iodine concentration due to diurnal fluctuations. Each participant provided two samples: one was tested immediately with a urine test strip (Combur3 Test VR E, GLU, PRO, ERY/Hb, Roche Diagnostics GmbH), and the other was left untouched as a control to serve as a baseline for comparison. This dual-sample approach allowed the researchers to directly assess the impact of the test strips on UIC measurements.
  In addition to the urine samples, 12 tap water samples were collected to further investigate the potential contamination. Some of these tap water samples were exposed to the same type of urine test strips for varying durations (10, 30, and 60 seconds) to simulate different exposure scenarios and to determine if the duration of contact influenced the extent of contamination. This experimental design provided a controlled environment to assess the potential iodine transfer from the test strips to the samples.
  Urinary iodine concentration (UIC) was measured using the Sandell–Kolthoff reaction, a well-established and reliable method for iodine quantification. This method involves a chemical reaction that produces a color change proportional to the iodine concentration in the sample, allowing for precise and accurate measurements. By using this standardized method, the researchers ensured that their findings were comparable to other studies and could be reliably interpreted.
• Findings

Mechanisms of Contamination

Test Strip Composition

Investigations into the composition of the test strips revealed that they contained iodine, primarily in the glucose (GLU) and erythrocyte (ERY) test pads. The GLU pad was specifically treated with iodine to reduce interference from ascorbic acid, a common substance that can affect the accuracy of glucose measurements. Meanwhile, the ERY pad incorporated an iodate mesh, which is used to enhance the detection of erythrocytes (red blood cells) in urine samples. Although the presence of iodine was not explicitly stated in the package inserts, confirmations from the manufacturers indicated that iodine could leach into urine samples during testing. This unintended iodine release posed a significant risk of contamination, particularly in tests designed to measure urinary iodine concentration (UIC).

Duration of Exposure

The extent of contamination was found to be directly proportional to the duration of test strip exposure. Even brief contact of just a few seconds was sufficient to introduce significant amounts of iodine into the samples. As the exposure time increased, so did the concentration of iodine, exacerbating the problem. This time-dependent increase in iodine contamination underscored the critical importance of strict adherence to sample collection protocols. Any deviation from the recommended procedures could lead to substantial contamination, rendering the UIC measurements unreliable. Therefore, it is essential for healthcare providers and researchers to follow precise guidelines when using these test strips to ensure accurate and valid results.

Implications for Iodine Nutrition Surveys

Inaccurate Data Interpretation

Contaminated urine samples lead to erroneous urinary iodine concentration (UIC) measurements, which in turn compromise the validity of iodine nutrition surveys. When urine samples are contaminated with iodine from test strips, the resulting UIC measurements can be significantly skewed. This inaccuracy can have serious implications for public health assessments and interventions. Overestimation of iodine intake can mask underlying deficiencies, delaying necessary interventions and potentially causing long-term health consequences. For instance, undetected iodine deficiencies during pregnancy can lead to developmental issues in children, such as cognitive impairments and growth delays. Conversely, falsely elevated UIC levels might suggest excessive iodine intake where none exists, leading to unnecessary dietary restrictions. Such restrictions could inadvertently reduce the intake of iodine-rich foods, which are essential for maintaining thyroid function and overall health.

Public Health Risks

Accurate iodine nutrition data is crucial for formulating public health policies and dietary guidelines. These policies and guidelines are designed to ensure that populations receive adequate nutrition and prevent iodine-related disorders, such as iodine deficiency disorders (IDD) and iodine-induced hyperthyroidism. Contamination from test strips undermines these efforts by introducing inaccuracies into the data. This can risk the health of vulnerable populations, particularly pregnant women and children, who are most susceptible to the effects of iodine imbalances. Misguided recommendations based on contaminated data could exacerbate iodine-related disorders, potentially leading to widespread health issues. For example, incorrect assessments of iodine status could lead to inappropriate iodine supplementation programs or dietary advice, which might do more harm than good. Therefore, it is essential to implement rigorous sample handling protocols to minimize contamination and ensure the reliability of UIC measurements. By doing so, public health initiatives can be based on accurate data, thereby effectively addressing iodine nutrition needs and protecting the health of the population.

Strategies for Mitigation

• Protocol Revision
  To prevent contamination, study protocols must explicitly outline procedures for urine sample collection and handling. This includes using dedicated, iodine-free utensils for sample collection and storage, and avoiding contact with test strips or any other potential contaminants. Clear instructions should be provided to participants and researchers to ensure strict adherence.
• Quality Control Measures
  Incorporating blanks or control samples with known iodine content can help identify and quantify contamination. These controls should undergo the same handling procedures as test samples, allowing researchers to detect and correct for any deviations. Regular calibration and maintenance of analytical equipment are also essential to ensure accurate iodine measurements.
• Alternative Testing Methods
  Exploring alternative, non-contact methods for urine analysis could eliminate the risk of contamination. For instance, advanced spectroscopic techniques or point-of-care devices that do not require physical contact with the sample might offer viable solutions. However, these methods must undergo rigorous validation to ensure their accuracy and reliability.

Conclusion

The Faroe Islands study serves as a stark reminder of the hidden dangers lurking in seemingly routine diagnostic procedures. Urine test strips, while invaluable for quick medical diagnostics, can significantly contaminate urine samples with iodine, leading to inaccurate UIC results. This contamination not only compromises the validity of iodine nutrition surveys but also poses significant public health risks.

To mitigate these risks, researchers must revise their protocols, incorporating stringent quality control measures and exploring alternative testing methods. By doing so, we can ensure accurate iodine nutrition data, guiding effective public health interventions and safeguarding the health of populations worldwide. As we continue to monitor and address iodine nutrition, let this study serve as a catalyst for change, driving us towards more rigorous and reliable scientific practices.

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