The estimation of systemic arterial hypertension (SAH) through self-reporting questionnaires in population-based surveys presents advantages, such as low cost, simplicity of measurement, and ease of application. However, as with any diagnostic test, classification errors are expected to occur, with inevitable false-positive and false-negative cases. Thus, a certain proportion of people will report having the disease when in fact they do not have it, and a group of people will report being healthy when they are actually sick.^{1 , 2}

To quantify the accuracy of this procedure for SAH measurement, it is possible to calculate self-reported SAH sensitivity and specificity indicators, using a reference standard. The most common “gold standards” for this are the use of sphygmomanometers^{1 , 2} and of automatic measurement devices.^{3 - 5} Results found for sensitivity in these studies varied from 0.45⁴ to 0.84³ , and, for specificity, from 0.81⁵ to 1⁴ .

Concerning the question used for self-assessment, most studies^{1 - 3} question if any doctor or health professional had ever claimed that the subject had arterial hypertension or “high pressure”. As objective as this question may seem, there is always a degree of subjectivity within it, making its understanding difficult. For example, it is known that gender, age, schooling, the way the question is asked, and the type of interview (face-to-face or telephone) may influence answers, adding to the uncertainty introduced by the use of different gold standards and cut-off points for diagnosis.

In addition, the validation of self-reported morbidity is influenced by cultural and economic characteristics of a population, as well as by the operating health system. Self-reported morbidity depends on access to health care, and it may be assumed that populations with a similar health system (e.g. a “universal health system”) will behave similarly in this respect.

In light of the above, the objective of this study was to estimate combined measures of sensitivity and specificity for self-reported SAH, using only studies performed in Brazil (therefore sharing similar cultural, economic, and access to health characteristics). A systematic review and a meta-analysis were developed for this purpose.

A total of 2,610 references were found through the database search. After the exclusion of duplicates, 1,388 studies were evaluated by title and abstract, and 113 studies were selected. These 113 studies were completely analyzed, and 24 were further selected. Of these, seven had been conducted in Brazil, one of these used only adolescent subjects and was excluded, and one of these used only elderly subjects and was excluded. Thus, five studies were finally included in the qualitative analysis,

Of the five studies above, four did not have all the necessary statistical information for a metaanalysis. E-mail contacts were successful in retrieving information for three of these, thus resulting in four studies for the meta-analysis.

Figure 1 shows the flow chart for the studies identified, screened, assessed for eligibility, excluded, and finally included in the analyses. No further study could be identified by personal (e-mail) consultation with researchers in the area.

Figure 1

Table 1 presents the characteristics of the studies in the systematic review and meta-analysis. The most common gold standards were sphygmomanometers. Table 2 shows the risk of bias in these studies. The domain with the smallest risk was "Flow and Time", and the domains “Patient Selection” and “Index Test” had the highest occurrence of high/unclear risk.

Table 1

Study	Use of defined question	Reference standard	Samplesize	Minimum age	Sensitivity	Specificity
Lima-Costa et al, 2004	Yes	Esfigmomanometer	970	18	0.72	0.86
Chrestaniet al, 2007	Yes	Authomatic monitor	2906	20	0.84	0.87
Selem, et al 2013	No	Authomatic monitor	535	20	0.71	0.80
Louzada et al, 2010	Not reported	Esfigmomanometer	349	No treported	0.45	1.00
Campos et al, 2011	Yes	Esfigmomanometer	67	18	0.43	0.89

Table 2

Study	RISK OF BIAS				APPLICABILITY CONCERNS
	Patient Selection	Index test	Reference standard	Flow and Time	Patient Selection	Index test	Reference standard
Lima-Costa, 2004	☺	☺	☺	☺	☺	☺	☺
Chrestani, 2007	☺	☺	☺	☺	☺	☺	☺
Selem, 2013	?	?	☺	☺	☺	☹	☺
Louzada, 2010	☹	?	☺	☺	?	?	☺
Campos, 2011	☺	☹	☺	☺	☺	☹	☺

☺ Low risk ☹ High risk ? Unclear risk

The forest plots for sensitivity and specificity according to the study are presented in Figure 2 . The highest sensitivity was found in Chrestani et al.³ (S = 84%) and the lowest in Louzada et al.⁴ (S = 45%). By contrast, the latter presented a specificity of 100%, with the lowest E found in Selem et al. (E = 81%). The four studies that met the eligibility criteria are presented in Figures 2a and 2b. For both S and E, a high degree of heterogeneity was found, with I²> 98% and a statistically significant χ² (p <0.0001). Thus, a random effects model was used to estimate the combined value of S and E, resulting in S = 0.768 (95% CI: 0.745-0.790) and E = 0.875 (95% CI: 0.863-0.886). The small number of studies hindered the development of a meta-regression to assess the influence of study characteristics on sensitivity/specificity or to evaluate publication bias.

Figure 2

This study performed a systematic review of and a meta-analysis on self-reported SAH validation studies from Brazil. Five studies were included in the systematic review, four of which were eligible for the meta-analysis. The accuracy of the self-reported hypertension measurement can be considered satisfactory, as it was possible to correctly identify 77% of the people who truly had the disease (sensitivity), together with a specificity close to 88%, showing a high capacity to detect true non-patients. This information, however, should serve as a warning to researchers dealing with population surveys, since it indicates that estimated self-reported hypertension may be quite divergent from real rates. The pooled sensitivity/specificity results were high, and clearly superior to review studies conducted with more heterogeneous populations. For instance, one systematic review aiming to identify the proportion of knowledge of the disease (i.e. whether people with hypertension were aware of their condition) found a combined sensitivity of 58.4%¹² but included studies from many countries. Another similar study used two of the papers analyzed here, finding a combined sensitivity of 42% and a specificity of 90%,¹³ most likely due to the greater heterogeneity of its studies.

As expected, the study of a similar population (country) makes results more comparable, with a higher combined sensitivity. However, it should be noted that this problem does not arise in the validation of exam procedures, such as resonance versus tomography , since differences will mainly concern equipment validity and accuracy, and not the social and cultural characteristics of studied populations.

The use of self-reporting questionnaires to estimate the prevalence of hypertension may result in severe bias, and some studies present mathematical methods for dealing with this problem (e.g. ^{14 - 16} ). However, knowledge on the sensitivity/specificity of measurement procedures in a specific population is a fundamental step in these correction methods.^{14 - 16} Therefore, the estimates presented here can be useful to obtain better HAS estimates in the analyzed population.

Brazil has a history of population-based health surveys, such as the Health Supplement of the National Household Survey (PNAD), which later gave rise to the National Health Survey (PNS); and VIGITEL – a telephone-based surveillance system for risk factors in chronic diseases,¹⁷ These studies have been conducted throughout the country, allowing, over the years, for a solid basis for epidemiological research and resulting in several self-reported morbidity studies.

Although the separate measures of sensitivity and specificity represented the main objective of this study, Lee et al.¹⁸ point out that analyzing these measures separately (disregarding their correlation) can produce incorrect results and that studies should use the same explicit diagnostic limit.^{18 , 19}

A limitation of the present study was the small number of studies that fulfilled all the characteristics required for analysis. In addition, despite attempts of direct request, missing information for one of the eligible studies could not be recovered. Furthermore, reference tests, although considered as gold standards, may also have problems in the diagnosis of hypertension. In fact, the best method for SAH diagnosis (greater S and E) is Ambulatory Blood Pressure Monitoring (ABPM). However, the complexity and time needed for ABPM application render its use difficult in population surveys, and apparently no study used this method as a gold standard for the validation of self-reported SAH.

Self-reporting has been frequently used for the population screening of SAH, since it is considered to be a valid and relatively cheap procedure. This estimation method may result in bias, but this problem can be reduced with the help of the measurement sensitivity and specificity values. Therefore, the results presented here would allow for health policies based on more reliable data, as government agencies need to know the epidemiological profile of a population, and high-coverage surveys are commonly used for this purpose.

Although the combined values presented here were higher than those that would be used if only one of the analyzed studies were to be considered (sensitivity above 75% and specificity close to 90%), researchers must take into account that the procedure still fails to detect a significant proportion of subjects with the disease.

In summary, the restriction to studies from a similar population allowed for a better characterization of the validity of self-reported hypertension, with combined sensitivity and specificity values higher than those found in studies conducted in several populations. Thus, systematic reviews of self-reported morbidity should consider the use of sub-groups in order to obtain more consistent estimates.