The Effect of Household-based Screening on Blood Pressure Changes in South Africa

The Effect of Household-based Screening on Blood Pressure Changes in South Africa: a Regression Discontinuity Study

This study will evaluate the effect of household-based screening and care encouragement for blood pressure on subsequent changes in blood pressure. The study uses a quasi-experimental regression discontinuity design with existing population-based secondary data from the 2008, 2010, 2012, 2014, and 2017 waves of the National Income Dynamics Study in South Africa.

Study Overview

• Status: Completed
• Conditions: Hypertension; Blood Pressure
• Intervention / Treatment: Other: Household blood pressure screening with care encouragement

Detailed Description

Household-based screening and referral to care for blood pressure may improve blood pressure control at the population level in many low- and middle-income countries.

This observational study will use a quasi-experimental regression discontinuity design to evaluate the effect of household-based screening for blood pressure with care encouragement for potentially hypertensive individuals on subsequent changes in blood pressure over time.

Individuals had their blood pressure measured in the household as part of the National Income Dynamics Study data collection. If individuals had a measured blood pressure in the hypertensive zone, they were told that they had elevated blood pressure, that high blood pressure can lead to life threatening consequences, and that they should seek further care. The study exploits the fact that individuals were given this information based on a hard blood pressure cutoff. Therefore, the investigators will evaluate the causal effect of this household-based intervention in the absence of randomization by comparing individuals with a baseline blood pressure just above and below the cut off.

• Study Type: Observational
• Enrollment (Actual): 3986

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 30 years and older (Adult, Older Adult)
• Accepts Healthy Volunteers: N/A
• Genders Eligible for Study: All

• Sampling Method: Probability Sample

Study Population

Individuals will be drawn from the 2008, 2010, 2012, and 2014 waves of the National Income Dynamics Study (NIDS) with the 2017 wave used only for follow-up. The NIDS is a nationally representative, household-based, survey of families and individuals from across South Africa.

Description

Inclusion Criteria:

• Age greater than or equal to 30
• Valid blood pressure measurements

Exclusion Criteria:

• Prior diagnosis of hypertension
• Currently taking medication for blood pressure
• Measured with a blood pressure above 140 mmHg systolic or 90 mmHg diastolic in a previous wave of data

Study Plan

How is the study designed?

Design Details

• Observational Models: Other
• Time Perspectives: Prospective

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Intervention group; The intervention group consists of individuals with a measured blood pressure just above the hypertensive cut-off of 140 mmHg systolic or 90 mmHg diastolic blood pressure who have never previously been diagnosed as hypertensive and are not taking medication to lower their blood pressure. The exact upper bound on blood pressure will be determined empirically. Individuals in the intervention group were told that that their blood pressure was high, that high blood pressure can lead to life threatening consequences, that blood pressure control can reduce these negative consequences, and that they should seek follow-up care for their blood pressure.	Other: Household blood pressure screening with care encouragement; During the household survey visit, survey enumerators collected two measurements of the respondent's blood pressure. If either of the measurements exceeded 140 mmHg systolic or 90 mmHg diastolic, enumerators told participants: "Your blood pressure readings are higher than normal. High blood pressure is dangerous because it makes the heart work too hard. High blood pressure increases the risk of heart disease and stroke. High blood pressure can also cause other problems, such as heart failure, kidney disease, and blindness. You can control high blood pressure by taking action." Then the enumerators recommend that an individual seek medical care within 2 months.
Control group; The control group consists of individuals with a measured blood pressure just below the hypertensive cut-off of 140 mmHg systolic and 90 mmHg diastolic blood pressure who have never previously been diagnosed as hypertensive and are not taking medication to lower their blood pressure. The exact lower bound on blood pressure will be determined empirically. These individuals were not given the care encouragement intervention.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Two-year change in systolic blood pressure	For each survey wave, blood pressure is measured at the household by a trained enumerator using an electronic blood pressure device. The enumerators take two separate measurements during the course of the visit with at least three minutes between measurements with individuals in a seated position. The investigators will take the average of the two systolic blood pressure measurements as their main outcome measure.	Approximately two years based on the difference between survey waves in the years 2008, 2010, 2012, 2014, and 2017
Nine-year change in systolic blood pressure	For each survey wave, blood pressure is measured at the household by a trained enumerator using an electronic blood pressure device. The enumerators take two separate measurements during the course of the visit with at least three minutes between measurements with individuals in a seated position. The investigators will take the average of the two systolic blood pressure measurements as their main outcome measure.	Baseline in 2008 and approximately nine years later in 2017.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Health-seeking behavior	Health-care utilization is measured at the household based on respondents' answer to the survey question: "When did you last consult someone about your health?"	Cross-sectionally in 2010, 2012, 2014, and 2018
Blood pressure treatment	Whether an individual is currently taking treatment to control their blood pressure is measured during the household survey based on the answer to the question: "Are you currently taking medicine for high blood pressure?"	Cross-sectionally in 2010, 2012, 2014, and 2018

Collaborators and Investigators

• Sponsor: Till Bärnighausen
• Collaborators: Emory University
• Investigators: Principal Investigator: Nikkil Sudharsanan, PhD, Research group leader

Study record dates

Study Major Dates

• Study Start (Actual): February 1, 2008
• Primary Completion (Actual): December 1, 2017
• Study Completion (Actual): December 1, 2017

Study Registration Dates

• First Submitted: November 30, 2018
• First Submitted That Met QC Criteria: November 30, 2018
• First Posted (Actual): December 3, 2018

Study Record Updates

• Last Update Posted (Actual): December 7, 2018
• Last Update Submitted That Met QC Criteria: December 5, 2018
• Last Verified: December 1, 2018

More Information

Terms related to this study

• Keywords: Causal inference; Regression discontinuity
• Additional Relevant MeSH Terms: Cardiovascular Diseases; Vascular Diseases; Hypertension
• Other Study ID Numbers: RDD - BP - South Africa

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: Yes
• IPD Plan Description: The data are already publicly available at: http://www.nids.uct.ac.za/nids-data/data-access
• IPD Sharing Time Frame: Data are already available.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No