Verification of records over a period of three years (2004-06), showed that out of a total of 18452 donors, 951 were deferred and, among them 175 were due to hypertension. Thus about 0.95% of healthy blood donors had undetected hypertension. Characteristics of the study and control subjects are presented in . The mean age at detection of hypertension in the study group was 35.44 ± 7.69 yrs with a range from 23 to 53 years. The incidence increased with increasing age. The proportion of hypertensive's in the younger age group with less than 30 was 1.8% (12/681) followed by 10.6% (25/237) in the age group of 30-39 and 21.3% (13/61) in those above 40 years. There were only three females among the donors found to be hypertensive. This is in commensurate with the limited number of females donating blood. One significant observation is the higher body mass index in the hypertensive group compared to control group with odds ratio of 4.71 (95% CI 2.098-10.590 with P < 0.0001). Mean systolic and diastolic BP was higher in hypertensive group compared to normotensive control group with P value significant at 0.0001 . Among the hypertensive individuals, proportion of individuals with a pulse pressure of > 60 was significantly more . Family history of hypertension, CAD and stroke were significantly high among those with hypertension (P < 0.002, 0.006 and 0.001 respectively). The odds ratio for positive family history of hypertension was 2.325 (95% CI, 1.0162-5.324). The prevalence of parental consanguinity was higher among hypertensive, though the difference was not significant .
Systolic and Diastolic Blood pressure of Blood Donors
Pulse Pressure of Blood Donors
Family History and Consanguinity
Hypertension is an important cause of cardiovascular morbidity and mortality with high prevalence reported among middle aged individuals and positivity associated with increasing age and elevated BMI.[8
] It is being increasingly known that high BP is an important public health problem in developing countries.[9
] When an individual presents with cardiovascular or renal sequelae of chronic hypertension, the damage is usually done. It is therefore essential to detect and regulate blood pressure before it becomes symptomatic. About 1% of healthy individuals were found to have undetected hypertension. Though the study was not designed to determine the prevalence of hypertension in the region, this is likely a rough estimate of the proportion of undetected hypertensive in the local population, as donors can be considered as a representative of healthy individuals. The prevalence and causative factors vary between populations due to both genetic and environmental factors. Overweight, sedentary behavior, alcohol intake, higher social class, diabetes mellitus, salt intake and smoking are risk factors for hypertension, in most of the countries in Asia.[4
] The study showed a positive association with increasing age. Another important observation was the association of higher body mass index with hypertension. An increase in BMI above 27 has also been reported to be associated with high risk of CAD, hypertension and other chronic diseases.[11
] An increased pulse pressure is a good measure of the inelasticity of the arteries. It is linked to an increased risk of heart attack, heart failure and stroke. Pulse pressure higher than 60 was more frequently seen among untreated and newly detected hypertensive. Compared to other parameters, baseline pressure measurements including pulse pressure are the best predictors of cardiovascular mortality.[12
] There was also significantly higher incidence of positive family history among hypertensive . A number of life style modifications have been shown in clinical trials to lower BP and incidence of hypertension. These include weight loss in the obese, physical activity, moderation of alcohol intake, diet with increased fruits and vegetables and reduced saturated fat content, reduction of dietary sodium intake and increased potassium intake.[13
] Other risk factors associated with population transition from rural to urban economies also contribute to greater food consumption and sedentary life style.[19
] This study gives a rough estimate of the liability to hypertension among the apparently healthy population of the region. No significant differences were observed for the demographic variables like education, socio-economic status and place of residence. Physical activity, food habits, smoking and alcohol intake were comparable between the two groups of donors. None of the females reported the use of oral contraceptives.
Thus increasing age, higher BMI and positive family history can be considered as the major predisposing factors for hypertension in the local population. There is growing need for health education and health screening among the blood donors as well as the general population on hypertension awareness and preventive measures.[20
] Offering health screens appears to motivate many potential candidates for blood donation and is widely appreciated by them as a means of early health seeking. Awareness of hypertension among our blood donors is poor. Identification of plausible risk factors will help in planning interventional programs like dissemination of information on life style modification and health education.
Limitations of the study
One limitation of the study was the inability to confirm the hypertensive status by repeated recording of blood pressure at longer time intervals. Another possible bias is that only the apparently healthy individual volunteer to donate blood and some undetected hypertensive may not come to Blood Bank due to general feeling of malaise. Hence the estimate of hypertensive may be more. Donors are in the selected age group of 18 to 60 years and this is not likely to affect the results as hypertension becomes symptomatic generally in this age group.