Proteinuria can cause or exacerbate hypothyroidism, possibly due to urinary loss of protein-bound thyroid hormone. However, the precise relationship between proteinuria and hypothyroidism remains unclear.
Determine the prevalence of hypothyroidism in patients with proteinuria and the relationship between hypothyroidism and degree of proteinuria.
Retrospective cohort study (December 1979-March 2015).
Large academic hospital.
All paired samples of urine protein and serum thyrotropin (TSH), measured within 24 hours, obtained from adults (>18 years) with at least one instance of urine protein >0.2 g/day or mg/mg creatinine.
Samples were stratified by urine protein tertile. Mean TSH and risk of TSH elevation were compared among tertiles using ANCOVA and generalized estimating equations controlled for age, sex, samples per patient, and levothyroxine treatment.
2676 samples were identified from 2136 patients. Mean±SE TSH (mIU/L) was increased in the highest tertile of urine protein (>1.75 g/day) compared to the lower two tertiles (2.09±0.07 vs. 1.59±0.07, 1.59±0.06, p5 mIU/L (17.2% vs. 10.5%, 11.9%, p5 mIU/L (OR 1.44, 95%CI 0.67-3.09, p=0.35). The highest tertile also had a higher prevalence (6.2% vs. 3.4%, 2.6%, p=0.003) and risk (OR 1.72, 95%CI 1.05-2.84, p=0.008) of TSH >10 mIU/L. Similar results were observed when comparing samples with nephrotic-range proteinuria (>3.5 g/day) to those with lesser proteinuria.
Hypothyroidism is common among adults with proteinuria, and the risk of hypothyroidism is directly related to the severity of proteinuria.

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