The mean platelet volume is positively correlated with serum thyrotropin concentrations in a population of healthy subjects and subjects with unsuspected subclinical hypothyroidism.

BACKGROUND: A possible prothrombotic effect of elevated thyrotropin (TSH) has been suggested. The mean platelet volume (MPV), which is used to measure the platelet size, can reflect platelet activity. Although limited and inconsistent data regarding the effects of thyroid function on the MPV are available from small-scale case-control studies, no study has been based on a general population, particularly in euthyroid states. The objective of the present study was to determine whether there is an association between the MPV and serum TSH concentrations in an apparently healthy Korean population without overt thyroid disease, but including subjects with unsuspected subclinical hypothyroidism (SCH).

METHODS: We retrospectively studied 6893 asymptomatic Korean adults who were 20 years of age or older and who underwent voluntary regular health check-ups at the Health Promotion Center of Chosun University Hospital. The subjects who met the inclusion and exclusion criteria were subdivided into four groups, such as tertile groups for the TSH reference range and an SCH (TSH ≥4 μIU/mL with a normal free T4 concentration) group according to the TSH level. We compared the mean values of the MPVs among the groups. Multivariate logistic regression analyses were used to identify associations between the highest tertile of the MPV and the TSH subgroups.

RESULTS: The mean level of the MPV in all study subjects was 8.12±0.75 femtoliters (fL), and the mean value of the MPV was significantly different in each group. The mean MPV in SCH was significantly higher compared with those of the first tertile (T1) and second tertile (T2). Moreover, the mean MPV increased statistical significantly by increasing tertiles of the TSH concentration and was highest in SCH (T1, 8.08±0.81 fL; T2, 8.09±0.62 fL; T3, 8.13±0.77 fL; SCH, 8.21±0.81 fL; p for trend=0.012). After adjusting for risk factors associated with increasing MPVs and platelet counts, SCH was independently associated with the highest tertile of the MPV (all subjects, odds radio (OR) 1.58 [95% confidence interval (CI) 1.19-2.09]; men, OR 1.70 [CI 1.10-2.64]; women, OR 1.55 [CI 1.06-2.26]).

CONCLUSIONS: The MPV was positively correlated with the TSH level. SCH is an independently associated factor with the highest tertile of MPV in a general Korean population. We propose that the MPV may contribute to the prothrombotic condition that is associated with SCH and perhaps even in putative euthyroid states where the TSH level is the higher part of the normal range.