Background: We aimed to evaluate the effects of seasonal changes on urinary specific gravity, blood pressure and urinary erythrocyte number in children living in Mediterranean climate.

Material/methods: The study was conducted on 547 children who presented for routine follow up to healthy-child care department between January 1997 and December 2002. Age, sex, weight, height, blood pressure, urinary specific gravity and urinary erythrocyte number were recorded by retrospective evaluation of files. Then, the parameters during summer were compared with those during winter. Additionally, correlation between the blood pressure, urinary specific gravity and urinary erythrocyte number was assessed separately during summer and winter.

Results: Anthropometrical measurements and mean age of the patients in summer and winter groups were similar. There was no significant change in urinary specific gravity (p > 0,05), while systolic and diastolic blood pressures were significantly higher in winter (p = 0.031 and p = 0.028 respectively). Temperature and humidity levels did not change significantly among different years but mean air temperatures during summer positively correlated with time from 1997 till 2002 (r = 0.965, p = 0.002). Blood pressure and urinary specific gravity were not correlated to each other at any time. Contrarily, there was a positive correlation between urinary specific gravity and erythrocyte number in summer (p = 0.01). The number of children with hematuria and degree of hematuria did not differ significantly between summer and winter.

Conclusions: Seasonal changes in Mediterranean climate do not lead to changes in hydration status or in urinary erythrocyte number in children. Therefore, the decrease in blood pressure during summer can not be attributed to the hydration status.