Ambulatory blood pressure monitoring (ABPM) is now recommended by NICE for use in the diagnosis of hypertension (1).

If blood pressure measured in the clinic is 140/90 mmHg or higher:

• take a second measurement during the consultation
  • if the second measurement is substantially different from the first, take a third measurement. Record the lower of the last two measurements as the clinic blood pressure

If the clinic blood pressure is 140/90 mmHg or higher, offer ambulatory blood pressure monitoring (ABPM) to confirm the diagnosis of hypertension. If a person is unable to tolerate ABPM, home blood pressure monitoring (HBPM) is a suitable alternative to confirm the diagnosis of hypertension

If the person has severe hypertension, consider starting antihypertensive drug treatment immediately, without waiting for the results of ABPM or HBPM

Ambulatory blood pressure monitoring

• when using ABPM to confirm a diagnosis of hypertension, ensure that at least two measurements per hour are taken during the person's usual waking hours (for example, between 08:00 and 22:00).
• use the average value of at least 14 measurements taken during the person's usual waking hours to confirm a diagnosis of hypertension

Notes:

• Classification of hypertension

  • stage 1 hypertension
    • clinic blood pressure is 140/90 mmHg or higher AND
      • subsequently Ambulatory blood pressure monitoring (ABPM) daytime average OR Home blood pressure monitoring (HBPM) average blood pressure is 135/85 mmHg or higher
  • stage 2 hypertension
  • clinic blood pressure is 160/100 mmHg or higher AND
    • subsequently ABPM daytime average or HBPM average blood pressure is 150/95 mmHg higher
  • severe hypertension
  • clinic systolic blood pressure is 180 mmHg or higher or clinic diastolic blood pressure is 110 mmHg or higher
    
    

• Possible indications for ambulatory blood pressure monitoring (ABPM) were outlined in previous BHS guidance (2):

  • if there is unusual variability of clinic blood pressure measurements
  • if there are symptoms suggestive of hypotension
  • to aid the diagnosis of 'white coat hypertension'
  • informing equivocal treatment decisions
  • evaluation of nocturnal hypertension
  • evaluation of drug resistant hypertension
  • determining the efficacy of drug treatment over 24 hours
  • diagnosis and treatment of hypertension in pregnancy
    
    
• study evidence has revealed increased mortality in patients with higher night-time than daytime blood pressure (3)
  • study authors suggest that this probably indicates reverse causality
  • findings support recording the ambulatory blood pressure during the whole day
• readings from clinic and ambulatory blood pressure devices, when used side-by-side, may differ from one another and from true arterial pressure because they use different methods and assumptions
• average ambulatory readings from a series of patients, taken over 24 hours, are commonly lower than clinic readings by between 10/5 and 20/10 mmHg
• only validated well-maintained machines with appropriate cuff sizes should be used for ambulatory blood pressure monitoring ((ABPM) (also known as 24 hour blood pressure monitoring)

Reference:

• (1) NICE (August 2011) Management of hypertension in adults in primary care.
• (2) Williams B, Poulter NR, Brown MJ, Davis M, McInnes GT, Potter JF, et al. Guidelines for management of hypertension: report of the fourth working party of the British Hypertension Society, 2004.BHS IV. J Hum Hypertens 2004;18: 139-85
• (3) Boggia J et al. Prognostic accuracy of day versus night ambulatory blood pressure: a cohort study.Lancet. 2007 Oct 6;370(9594):1219-29