Evidence map›Paper›PMID 41240297›Full record

Observational studyBiological trace element research2026

Sample Size and Optimal Timing for Urine Collection Based on Diurnal Variability of Urinary Iodine/Creatinine Ratio in Pregnant Women.

Qi Meng, Min Fu, Rui Yang, Fei Li, Junjing Li, Meina Ji, Qi Jin, Mengxin Liu, Hexi Zhang, Wenxing Guo and 1 more

Abstract readObservational Study
PubMed Publisher
In one paragraph

Observational study in Biological trace element research, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 1 paper.

0numbers the graph read from it
0cells of the map it votes in
1citing papers in PubMed
–field-weighted citation impact
1 · What the graph read from it

What it found

Each row is one number read from the abstract, on the scale the paper reported it, with its interval. Left of the dashed line favours the treatment, right favours the comparator. Under each row is the sentence it came from. New to these charts? A ten-minute tutorial.

The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.

2 · The registry

The trial behind it

Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.

Neither the registry nor the abstract names a trial number. If this is a trial report, that itself is worth knowing.

3 · Its place in the literature

Who cites it

1 citing paper in PubMed.

  1. Article
4 · The record

Corrections and comments

PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.

5 · Who and what money

Authors and funding

11 authors.

Qi Meng *Department of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, 300070, China.
Min Fu *Tianjin Institute of Gynecology Obstetrics, Tianjin Central Hospital of Gynecology Obstetrics, Tianjin, China.
Rui Yang *Department of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, 300070, China.
Fei LiDepartment of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, 300070, China.
Junjing LiDepartment of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, 300070, China.
Meina JiDepartment of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, 300070, China.
Qi JinDepartment of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, 300070, China.
Mengxin LiuDepartment of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, 300070, China.
Hexi ZhangDepartment of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, 300070, China.
Wenxing GuoDepartment of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, 300070, China. guowenxing@tmu.edu.cn.ORCID http://orcid.org/0000-0002-5669-4836
Wanqi ZhangDepartment of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, 300070, China. wqzhang@tmu.edu.cn.ORCID http://orcid.org/0000-0002-6044-1137

Funding

National Natural Science Foundation of China 82230113
6 · The paper itself

Abstract

Urinary iodine concentration (UIC) is influenced by variable urine volume, undermining its reliability. The urinary iodine/creatinine ratio (UI/Cr) may provide a more stable measure, especially in pregnancy. This study aimed to explore the variation of UI/Cr in assessing iodine status in pregnant women, and determine the sample size and optimal sampling time for accurate assessment. Thirteen pregnant women participated in a seven-day iodine metabolism study. All urine samples from each participant were collected separately over the 7-day period, and urinary iodine and urinary creatinine were tested. Spot UIC was positively correlated with time interval (β = 12.09, P < 0.001). UI/Cr, an indicator corrected for volume effect, showed no significant effect with time interval (β = -3.00, P = 0.090). The CV of UI/Cr was lower than UIC at both individual (56.16% vs. 73.15%) and population levels (62.41% vs. 84.75%). With a 95% confidence interval and ± 20% precision, an individual needs 33 urine samples, while a population requires 39 samples. The mixed-effects model analysis revealed that spot UI/Cr during the 18:00-23:59 period exhibited the strongest correlation with 24-hour UI/Cr (β = 0.62, P < 0.001). Additionally, spot UI/Cr during the 12:00-17:59 period demonstrated the strongest correlation with 24-hour urinary iodine excretion (β = 0.61, P < 0.001). The UI/Cr provides a more reliable estimate of iodine status than UIC. To obtain a precision of ± 20%, 33 spot-urine samples are required for individual assessment and 39 for population-level evaluation. We recommend urine collection between 12:00 and 18:00 for accurate evaluation.

Indexed as

CreatinineIodinePregnancyUrine Specimen CollectionAdultCircadian RhythmFemaleHumansRenal EliminationSample SizeThyroid GlandTime FactorsCreatinineIodineIodine/creatinine ratioPregnant womenSample sizeSampling timeUrinary iodineVariation

Identifiers

PMID41240297

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Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.