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Hypertension has been identified as the third leading risk factor for disease burden worldwide [1]. It has been estimated that 29% of the world population will suffer from high blood pressure by the year 2025, that men and women have similar overall prevalence of hypertension, and that such prevalence increase with age consistently in all world regions [2].

According to the World Health Organization, the total prevalence of high blood pressure in Pakistan is estimated to be 25.2% [3]. It also estimates hypertension to cause 7.5 million deaths annually [4].

Hypertension is defined as a Systolic Blood Pressure (SBP) of 140 mmHg or more, or a Diastolic Blood Pressure (DBP) of 90 mmHg or more, or taking antihypertensive medication [5].

Based on the recommendations of the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure (JNC 7), blood pressure for adults aged 18 years or older has been classified into four categories as normal, prehypertension, stage 1 hypertension and stage 2 hypertension: Normal-systolic<120 mmHg, diastolic<80 mmHg; Prehypertension-systolic 120-139 mmHg, diastolic 80-89 mmHg; Stage 1 Hypertension-systolic 140-159 mmHg, diastolic 90-99 mmHg and Stage 2 Hypertension-160 mmHg or greater, diastolic 100 mmHg or greater [6].

Although nocturia is known to be multifactorial, available literature, scarce at best, does not relate elevated blood pressure level with increased urinary frequency [7-9].

A thorough literature search did not reveal ample pertinent data assessing such a relationship, especially in Pakistan. In order to establish a relevant local data base, this study was therefore intended to determine the association between blood pressure levels and urinary frequency in hypertensive patients.

After taking ethical approval, across-sectional study was carried out in the outpatient department of a secondary care hospital of Karachi among patients with self-reported history of hypertension and on antihypertensive medication.

The study sample consisted of a total of 292 patients, aged 18 or above, included in the study by convenient sampling. History of diabetes, cardiac events, neurological disorders, cluster headache, gastrointestinal disease, visual problems, and morbid obesity were exclusion criteria of the study.

After taking informed consent, participants’ relevant information was collected by means of a structured questionnaire designed specifically for the study whereas their blood pressure level was measured with the help of sphygmomanometer using stethoscope.

The data were entered and analyzed on SPSS version 20. Chi-square test of independence was applied to determine the association between blood pressure levels and the urinary frequency whereas the significance level was set at 0.05. The duration of the study was 6 months.

The study results revealed a significant positive association between both systolic and diastolic blood pressure levels and increased urinary frequency (p=0.047 and p=0.045 respectively) where stage 1/stage 2 hypertensive patients were more likely to have increased urinary frequency than those who were normotensive/pre-hypertensive (45.1% vs. 33.0% and 46.9% vs. 35.4% respectively) (Table 1).

Table 1: Overall association between blood pressure levels and urinary frequency.

After stratifying on the basis of gender it was seen that among male patients a significant positive association was found only between diastolic blood pressure level and increased urinary frequency (p=0.026) where stage 1/stage 2 hypertensive patients were more likely to have increased urinary frequency than those who were normotensive/pre-hypertensive (53.5% vs. 35.4%) (Table 2).

Table 2: Association between blood pressure levels and urinary frequency in males.

After stratifying on the basis of gender it was seen that among female patients none of the systolic or diastolic blood pressure levels were significantly associated with increased urinary frequency (Table 3).

Table 3: Association between blood pressure levels and urinary frequency in females.

After stratifying on the basis of age it was seen that among ≤ 49 year old patients none of the systolic or diastolic blood pressure levels were significantly associated with increased urinary frequency (Table 4).

Table 4: Association between blood pressure levels and urinary frequency among ≤ 49 years old.

After stratifying on the basis of age it was seen that among ≥ 50 year old patients a significant positive association was found between both systolic and diastolic blood pressure levels and increased urinary frequency (p=0.026 and p=0.015 respectively) where stage 1/stage 2 hypertensive patients were more likely to have increased urinary frequency than those who were normotensive/pre-hypertensive (55.3% vs. 32.3% and 59.7% vs. 37.9% respectively) (Table 5).

Table 5: Association between blood pressure levels and urinary frequency among ≥ 50 years old.

The study results revealed a significant association between both systolic and diastolic blood pressure levels and urinary frequency (p<0.05 for both) where patients with elevated blood pressure levels complained of higher frequency of urination than those whose blood pressure levels were controlled.

Moreover, after stratifying on the basis of gender and age, this association persisted only for diastolic blood pressure level in male patients and for both systolic and diastolic blood pressure levels in ≥ 50 year old patients (p<0.05 for all).

Nocturia is known to be most prevalent in females and in people of older age [7]. The preliminary study findings were therefore reassessed post gender and age based stratification to control for their potential confounding effects and, as expected, they were found to persist for diastolic blood pressure level in male patients only and for both systolic and diastolic blood pressure levels in ≥ 50 year old patients only, indicating that the initial results were indeed confounded by both gender and age of the study participants.

Several factors have been implicated as a cause of increased urinary frequency at night, or at day for that matter, but literature is silent about any potential role of elevated blood pressure levels in such a phenomenon.

Hypertensive patients, even when on anti-hypertensive medication, don’t always have well controlled blood pressure levels [10]. As 41.1% of the study participants complained of increased urinary frequency, any potential role of their elevated blood pressure levels was worth investigating. Unfortunately, as a thorough literature search did not reveal any pertinent published data, a meaningful comparison of the study findings with earlier literature could not be made.

The prime limitation of the study was the use of convenient sampling technique because of time constraints.

The study findings revealed a significant positive association between both the elevated systolic and diastolic blood pressure levels and the increased frequency of urination but after age and gender based stratification, it held true only for diastolic blood pressure level in male patients and for both systolic and diastolic blood pressure levels in patients aged 50 years or above. Further evaluation of the study findings with better study designs and a larger sample size is recommended.

The authors report no conflict of interests.