What is Hypouricemia?
Age and Sex Factors
What types of groups often develop hypouricemia which causes lower blood uric acid levels?
Hypouricemia is Predominated by Genetic Factors
Hyperuricemia is affected by genetic and environmental factors and is mainly developed in adult males. Hypouricemia, on the other hand, is associated with genetic mutations except for secondary conditions due to drugs and other causes. Therefore, genetic factors have a stronger influence than lifestyle and living environment.
Low uric acid levels on their own do not cause diseases and there are no subjective symptoms. Almost all cases are found during medical checkups or comprehensive medical examination without prior awareness among patients and their family. Before the recent progress in research, it had been considered that “low uric acid levels never cause diseases nor problems” and had rarely been informed to patients.
Hypouricemia is Common in Japanese Females
Frequency of hypouricemia among all subjects is 0.14 – 0.22% for males and 0.25 – 0.40% for females, showing higher frequency in females in comparison with males. This is because of the criteria of hypouricemia which is having “blood uric acid levels of 2 mg/dL or less” and because uric acid levels tend to be lower in females compared to males.
Hypouricemia, which has no symptoms, is classified as either renal hypouricemia (where the uric acid in urine is not resorbed and is excessively excreted) or xanthinuria (where low uric acid levels are observed due to deficiency of enzyme which degrades purine in the body into urine acid). The majority of Japanese patients have renal hypouricemia. Hypouricemia is found to be common in Japanese people, and it is considered that the disease is affected not only by gender but also by race.
Uric Acid Levels in Females Slightly Increase After Menopause
A survey conducted on males and females in 24 prefectures in Japan showed a constant prevalence of hypouricemia among males in their 40s to 70s. On the other hand, females showed a decrease in prevalence with 0.6% for 40s, 0.5% for 50s, 0.4% for 60s.. While the survey did not confirm the presence of menopause, it is considered to be caused by the decrease in female hormones since 80% of Japanese female experience menopause when they are 45 – 54 years old.
Given the effect of female hormones that facilitate the excretion of uric acid to the outside of the body, it is considered that uric acid levels were increased due to a decrease of excretion of uric acid outside the body as a result of decreased secretion of female hormones after menopause.
（※）Wakasugi, M. et al. Association between hypouricemia and reduced kidney function: a crosssectional population-based study in Japan. Am. J. Nephrol. 41, 138-146 (2015).