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6. Definition of variables

6.1 Blood pressure

6.1.1. Specification of data

The measurement procedures are described in Section 1.4.2 of Part III of the MONICA Manual (1). Any variation between the RUAs in the measurement procedures and quality of the data are described in the reports  quality assessment of data on blood pressure (5) and quality assessment of data on hypertention control (6).

The following extract from the Core data transfer format - survey data of the MONICA Manual (1) specifies the format in which the data were transferred to the MONICA Data Centre:  

 

NAME VERSION SPECIFICATION AND CODES CHARACTERS
HIB 3,6,7  "Have you ever been told by a doctor or other 
health worker that you have high blood pressure?" 
1 = yes 
2 = no (if no, record 8 in item DRUGS) 
9 = insufficient data 		 |__|       

 

 
DRUGS 3,6,7 "Are you taking (in the last two weeks) drugs 
for high blood pressure?" 
1 = yes 
2 = no 
3 = uncertain 
8 if HIBP = 2 
9 = insufficient data 		 |__|      
BPRECD 6,7 "Have you had your blood pressure measured in 
the last year?" 
1 = yes 
2 = no 
9 = insufficient data 		 |__|        
 

The item BPRECD was introduced in the November 1990 version of the manual.

 
SYS      3,6,7 Systolic blood pressure (mm Hg), first measurement 
888 = no information available, although the person 
           attended the survey examination 
999 = person did not attend the survey examination 		 |__|__|__|

 
DIAST1  3,6,7 Diastolic blood pressure (mm Hg), first measurement 
888 = no information available, although the person 
           attended the survey examination 
999 = person did not attend the survey examination 		 |__|__|__|
RZ1      3,6,7 First blood pressure random zero (mm Hg) 
88 = random zero device was not used or no information 
        available about the 1st blood pressure measurement, 
        although the person attended the survey examination 
99 = person did not attend the survey examination 		 |__|__|      
SYST2    3,6,7 Systolic blood pressure (mm Hg), second measurement 
888 = no information available, although the person 
           attended the survey examination 
999 = person did not attend the survey examination 		 |__|__|__|
DIAST2 3,6,7 Diastolic blood pressure (mm Hg), second measurement 
888 = no information available, although the person 
           attended the survey examination 
999 = person did not attend the survey examination 		 |__|__|__|
RZ2 3,6,7 Second blood pressure random zero (mm Hg) 
88 = random zero device was not used or no information 
        available about the 1st blood pressure measurement, 
        although the person attended the survey examination 
99 = person did not attend the survey examination 		 |__|__|     

6.1.2. Systolic blood pressure

Table 6.1.2 reports distribution characteristics of systolic blood pressure (SBP), which was calculated as the mean of two measurements. If one of the two measurements was missing the other one was used, except in SWE-GOT where only the first measurement was used in all 3 surveys.  The measurement values were corrected for the random zero if the random zero device was used (see Table 2  of the quality assessment of data on blood pressure for the RUAs which used the random zero device).

More specifically, if  we have both systolic blood pressure measurements and the random zero device was used then systolic blood pressure is defined as a mean of two measurements SBP = ((SYST1-RZ1)+(SYST2-RZ2))/2. Otherwise, if the random zero device was not used then SBP = (SYST1+SYST2)/2.

6.1.3. Diastolic blood pressure

Table 6.1.3 reports distribution characteristics of diastolic blood pressure (DBP), which was calculated as the mean of two measurements. If one of the two measurements was missing the other one was used, except in SWE-GOT where only the first measurement was used in all 3 surveys.  The measurement values were corrected for the random zero if the random zero device was used (see Section 6.1.2).

6.1.4. Blood pressure categories

Table 6.1.4 reports the proportions of subjects in six blood pressure categories:

Category Definition
I SBP < 160 mmHg and DBP < 95 mmHg, on treatment for hypertension
II SBP >= 160 mmHg or DBP >= 95 mmHg, on treatment for hypertension
III SBP >= 160 mmHg or DBP >= 95 mmHg, not on treatment for hypertension, told about high blood pressure
IV SBP >= 160 mmHg or DBP >= 95 mmHg, not on treatment for hypertension, never told about high blood pressure
V SBP < 160 mmHg and DBP < 95 mmHg, not on treatment for hypertension, never told about high blood pressure
VI SBP < 160 mmHg and DBP < 95 mmHg, not on treatment for hypertension, told about high blood pressure

The categories were defined using variables SBP (the mean of the two measurements of systolic blood pressure), DBP (the mean of the two measurements of diastolic blood pressure), DRUGS and HIBP:

 

SBP  >= 160 mmHg or DBP  >= 95 mmHg 

YES

NO

ID
HIBP HIBP
1 2 9 1 2 9

DRUGS

 1 II II ID I I ID ID
2 or 8 III IV ID VI V ID ID
3 or 9 ID ID ID ID ID ID ID

ID means "insufficient data". The blood pressure measurement was regarded as "insufficient data" if SBP or DBP had insufficient data.

Note that the definitions differ slightly from those reported in the earlier MONICA data books. MONICA manuscript groups for blood pressure publications have reviewed the definitions and recommended the current one.

6.1.5 Blood pressure categories among persons with high blood pressure

Table 6.1.5 reports the proportions of blood pressure categories I-IV among the subjects who are known to have high blood pressure:

 

SBP  >= 160 mmHg or DBP  >= 95 mmHg 

YES

NO

ID
HIBP HIBP
1 2 9 1 2 9

DRUGS

 1 II II ID I I ID EX
2 or 8 III IV ID EX EX EX EX
3 or 9 ID ID ID EX EX EX EX

"EX" means that the subject is not known to have high blood pressure (SBP >= 160 mmHg or DBP >= 95 or DRUGS=1) and is therefore excluded from the analysis.

6.1.6 Have you had your blood pressure measured in the last year?

The November 1990 version of the MONICA Manual introduced the question: "Have you had your blood pressure measured in the last year?".  The proportion of the subjects whose blood pressure had been measured is reported in Table 6.1.6.

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