Simple renal cyst is the most common cystic deformation found in adults. However, there were a few systematic Korean reports for the clinical symptoms and complications of simple renal cysts. The author's purpose was to determine the relationship between simple renal cysts diagnosed by abdominal ultrasonography and hypertension.
Among 13,482 persons who took a routine physical examination at Ulsan University Hospital in 2002, 5,127 persons who took medical examinations again in 2010 were selected. We excluded persons who had renal cyst, hypertension, diabetes, liver cirrhosis, kidney disease, thyroid disease, and cancer in 2002. Analysis was conducted for 505 subjects with newly diagnosed simple renal cyst and 2,744 subjects without renal cyst in 2010. The simple renal cyst group was compared to a control group without renal cyst.
Among 3,249 subjects, simple renal cyst and hypertension were newly diagnosed in 505 subjects and 503 subjects. The subjects who had simple renal cysts had significantly higher hypertension incidence (odds ratio [OR], 1.53; 95% confidence interval [CI], 1.20 to 1.94). Significant hypertension incidence was observed especially when the subjects had cysts located on both kidneys (OR, 3.48; 95% CI, 2.12 to 5.71), two (OR, 3.08; 95% CI, 1.84 to 5.15) or more cysts (OR, 3.12; 95% CI, 1.38 to 7.04), and larger cysts more than 1 cm in diameter (OR, 1.55; 95% CI, 1.16 to 2.07).
The presence of simple renal cysts was significantly positively related to the incidence of hypertension. Bilateral distribution, two or more number, and larger size than 1 cm diameter were the characteristics of simple renal cyst related to hypertension.
Simple renal cyst consists of 70% of all asymptomatic kidney tumors which can be found in all age groups but its prevalence increases with age, more than 5% in age of 40's and 36% in 80's and is often diagnosed as an incidental findings.
Hypertension is one of the most common chronic diseases and in 2013 the World Health Organization reported that about 40% of the population over 25 years of age has been diagnosed with hypertension worldwide. The number of people diagnosed with hypertension worldwide has increased dramatically from 6 million in 1980 to 1 billion in 2008, and among 17 million deaths caused by cardiovascular disease every year, 9.4 million deaths are estimated to be hypertension related.
The second most common cause of death in Korea was cardiovascular disease, accounting for 19.5% of all causes in 2012. The importance of prevention and treatment of hypertension can easily be presumed from the above facts in terms of both individual and national health.
The relationship between simple renal cysts and hypertension has been reported by many studies,
Among 13,482 people who underwent general physical examination at Ulsan University Hospital from March to December 2002, 5,127 people who returned for another physical examination between March and December 2010 were initially selected. From the initial selections, 275 subjects with simple renal cyst, 340 subjects with diabetes, 1,260 with hypertension, 31 with liver cirrhosis, 52 with thyroid disease, 2 cancer patients, and 1 patient with kidney disease diagnosed by 2002 were excluded along with 542 subjects with insufficient information from surveys in year 2010. The remaining 3,249 subjects were analyzed in this study.
Both general physical examinations in 2002 and 2010 took general history surveys for factors such as smoking, drinking, physical exercise, medical history, and drug usage. Physical measurements were taken by skilled nurses.
Systolic and diastolic blood pressure was measured after at least 10 minutes of rest, sitting down. Hypertension was defined with current antihypertensive use or either systolic pressure over 140 mm Hg or diastolic pressure over 90 mm Hg with prior history of hypertension diagnosis. Diabetes was defined using diagnostic criteria based on reports from American Diabetes Association in 2010;
Statistical analysis was done using SPSS ver. 17.0 (SPSS Inc., Chicago, IL, USA). Factors such as age, BMI, diabetes, dyslipidemia, and social history (alcohol, smoking, and exercise) that can effect development of hypertension were adjusted using logistic regression. P-value of < 0.05 was defined to be statistically significant.
Among 3,249 targets, 3,032 (93.3%) were male. Average age was 54.0 ± 3.6 years and BMI was 23.5 ± 2.5 kg/m2. Average systolic and diastolic blood pressure was 120.4 ± 11.7 mm Hg and 77.8 ± 8.3 mm Hg, respectively. Alcohol use over three times in a week, regular exerciser, and current smokers were 12.7%, 42.9%, and 30.1% of the total, respectively (
Among 3,249 subjects (217 female and 3,032 male), 505 (15.5%) new renal cyst was diagnosed. Incidence by sex was higher in males (16.2%, 490/3,032) than females (6.9%, 15/217) (P < 0.001). Hypertension incidence was 15.5% (503/3,249) in all subjects and 20.6% in newly diagnosed simple renal cyst group.
Incidence of hypertension was higher in the newly diagnosed simple renal cyst group with odds ratio of 1.53 (95% CI, 1.20 to 1.94) compared to the non-simple renal cyst group. After adjustment for age, BMI, diabetes, dyslipidemia, alcohol, and exercise, odds ratio was 1.44 (95% CI, 1.13 to 1.84), showing increased risk of hypertension (
When simple renal cyst was unilateral, odds ratio was 1.29 (95% CI, 0.99 to 1.68) and no statistical significance was found. But with bilateral cysts, statistically significant increased risk of hypertension was observed with odds ratio of 3.48 (95% CI, 2.12 to 5.71). This result was also observed even after adjustment (
Total number of simple renal cyst was divided into three groups: one, two, and more than three. Each odds ratio was 1.25 (95% CI, 0.95 to 1.65), 3.08 (95% CI, 1.84 to 5.15), and 3.12 (95% CI, 1.38 to 7.04), respectively. With one simple renal cyst, no significant increased risk of hypertension was found but with two or more than three cysts, statistically significantly increased risk with positive correlation. The same was true even with after adjustment (
Largest diameter of less than and more than 1 cm was analyzed. Odds ratio was 1.49 (95% CI, 1.02 to 2.18) and 1.55 (95% CI, 1.16 to 2.07), respectively, with all groups to have increased risk of hypertension. But adjusted odds ratio in the two groups were 1.46 (95% CI, 0.99 to 2.16) and 1.44 (95% CI, 1.07 to 1.93), respectively, and increased risk in only diameter of more than 1 cm group was noted (
In this study, newly diagnosed simple renal cyst was found to be associated with increased risk of hypertension, especially when renal cyst was either bilateral, with more than 2 cysts or with largest diameter of more than 1 cm. The exact mechanism between simple renal cyst and hypertension is not known. Rho et al.
Increased risk of hypertension was noted when renal cyst was bilateral and with more than 2 cysts in this study. Based on theoretical view of compression of renal artery by the cyst, compensation by unaffected kidney against increasing blood pressure in cases of unilateral cyst can be presumed. With one simple renal cyst, it is 100% unilateral and with two cysts, 24.7% is unilateral and 75.3% is bilateral, underpinning the above theory.
The size of the renal cyst appears to have been related to the risk of hypertension in this study's results, but when the group with diameter of more than 1 cm was subdivided into more than 2 cm, 3 cm, and 5 cm, no significant increased risk was found. An important fact to take note of is that the larger the diameter of the cyst, size of the targets decreased rapidly for statistical analysis. Further studies with a larger population is needed. Incidence of renal cyst was 15.5%, similar to prevalence rate of 7.8% to 17.2% from local studies.
Prevalence rate of hypertension in this study was 15.5%, lower than previous reports from the KNHANES in 2007,
Although a certain relationship between simple renal cyst and hypertension was noted through this study, it is not enough to explain accurate order of relation. Terada et al.
In general, characteristics of subjects, decreased fasting blood sugar (FBS) but increased HbA1c was noted and decreased total cholesterol and triglyceride but increased high density lipoprotein was also noted. This may be explained as most subjects being employees of major companies in Ulsan have diligently corrected harmful life styles in the short term prior to examination to avoid any disadvantageous measures by the examination results. Hence although short term glycemic results (FBS) improved, long term glycemic results (HbA1c) have not been affected.
Limitations to this study may include the fact that the order of relation between hypertension and renal cyst was not taken into consideration at the point of study design. Further study is needed to clarify the order of relation between two conditions. Another limitation is that groups with multiple cysts were not further identified by distribution of cyst. Authors believe that regardless of number of the cyst, bilateral renal cysts may increase risk of hypertension and if this is true, compensation mechanism by unaffected kidney against increasing blood pressure may be backed up. Identification of the relationship between the cyst size and location within the kidneys with hypertension is also needed. Another limitation to take into account is the measurement reliability because abdomen ultrasonography was not always performed again by a single doctor in 2002 and 2010. If the relationship between simple renal cyst and hypertension is clarified through suggested measures above, increased risk of hypertension could be taken into account through observation and treatment of simple renal cyst with bilateral distribution, multiple cysts or large diameter as this study has shown.
No potential conflict of interest relevant to this article was reported.
General characteristics of study subjects (n = 3,249)
Values are presented as mean ± SD or number (%).
*Calculated as weight in kilograms divided by height in meters squared. †There are subjects with missing data.
Crude and adjusted OR of hypertension according to the presence of simple renal cysts
Using multiple logistic regression analysis.
OR, odds ratio; CI, confidence interval.
*Adjusted for age, body mass index (calculated as weight in kilograms divided by height in meters squared), diabetes mellitus, dyslipidemia, alcohol intake, exercise (of 2010).
Crude and adjusted OR of hypertension in groups by distribution of cysts, numbers, and size
Using multiple logistic regression analysis.
OR, odds ratio; CI, confidence interval.
*Adjusted for age, body mass index (calculated as weight in kilograms divided by height in meters squared), diabetes mellitus, dyslipidemia, alcohol intake, exercise (of 2010).