BACKGROUNDThe prevalence and the spectrum of thyroid dysfunction in the mainland of China are not adequately understood. We performed a population-based study to determine the prevalence of major thyroid dysfunctions including overt and subclinical hyper- and hypothyroidism in a stable cohort.

METHODSAll active and retired employees aged 20 years and older (11 067) of Sinopec Zhenhai Refining & Chemical Company in Ningbo participated in the cross-sectional survey with a questionnaire and blood samples.

RESULTSA total of 10 405 individuals attended for screening. Using biochemical definitions 95.5% were euthyroid. The prevalence of former diagnosed hyperthyroidism was 1.1% in females and 0.4% in males, hypothyroidism 1.7% and 0.3%, and thyroid surgery 1.2% and 0.3%, respectively. In both sex the prevalence increased with age. Twenty-four percent of individuals with thyroid surgery or medications had abnormal thyroid-stimulating hormone (TSH) levels. In individuals without a history of thyroid disease, the prevalence of pathological TSH values in females and males were TSH > or = 10 mU/L 0.60% and 0.29%; TSH 4.8-9.9 mU/L 5.71% and 2.25%; TSH < 0.3 mU/L 0.87% and 0.41%, respectively. Overt hyper- and hypothyroidism were uncommon (0.2%, 0.3%, respectively). The prevalence of subclinical hyper- and hypothyroidism was 0.4% and 3.4%, respectively. Subclinical hypothyroidism was more common in females (male 2.4% vs. female 5.8%, P < 0.001) and with increasing age (P < 0.001).

CONCLUSIONSThe prevalence of thyroid dysfunction is 4.5% in the cohort. Among individuals with thyroid medications or surgery, only 75.7% were within the normal range of TSH. These results indicate that thyroid dysfunction is common in Chinese adults.