The Relation To Clinic Bp

We have found a markedly lower day time BP (147/ 85 mmHg) than clinic BP (163/95 mmHg) in 102 consecutive NIDDM and IDDM patients referred to ambulatory BP measurement because of repeated clinic BP > 140/90 mmHg [124]. The frequency of white coat hypertension in normoalbuminuric diabetic patients is about 25 % [124,125]. If patients are selected for the presence of organ lesions related to hypertension (diabetic nephropathy) the proportion of white coat hypertension may be reduced [125]. One study reported a much higher frequency of white coat hypertension (41 %) probably due to a shorter observation period before labelling patients as hypertensive and because patients was designated as "true" normotensive on the basis of 24h BP (containing the lower night BP) rather than day time values [126]. Obviously the reported frequency of white coat hypertension also varies with the definition of a normal ambulatory BP [22,23]. An extremely high frequency of white coat hypertension (62 %) was reported in a study measuring clinic BP at one occasion only and using the same cut-off level for establishing the diagnosis of hypertension (clinic mean arterial BP > 100 mmHg) as for identifying those with apparent normal ambulatory BP (day time mean arterial BP < 100 mmHg) [127]. Also in adolescents a very high frequency of white coat hypertension has been disclosed [128]. A low frequency (11 %) was reported in NIDDM patients who was categorized as normotensive if day time BP was < 131/86 (women) and < 136/87 (men) [123]. For patients older than 60 years with isolated systolic hypertension the average systolic day time BP is reported much lower (about 20 mmHg) than clinic BP during the placebo run-in phase of the Syst-Eur trial also containing diabetic patients [129]. During a follow-up of 3.2 years the rate of cardiovascular events was comparable in normotensive and in white coat hypertensive diabetic subjects. Although the absolute number of events in the three groups were low the data suggest a benign clinical course of white coat hypertensive patients at least in the short term. The study showed a higher event rate in female "non-dippers" versus "dippers" [123]

Several international and national institutions now approve ambulatory BP monitoring in certain clinical circumstances [130-132]. The important problems about establishing a normal reference for ambulatory BP have been reviewed thoroughly [133]. Although large individual differences do exist, a clinic BP of 140/90 roughly corresponds to a day time average of 135/85 mmHg [133]. The present general recommendations (for non-diabetic patients) implies that a day time BP < 135/85, and a night BP < 125/75 mmHg is considered normal. Even lower cut off limits (< 125/80 mmHg) for a normal day-time BP has been suggested [131], however the background for this proposal can be questioned indeed [134]. A pertinent question is the optimal goal for ambulatory BP in diabetes. Clearly this depends on coexisting risk factors like microalbuminuria or previous cardiovascular events. While daytime BP usually is lower than clinic BP for (clinic) hypertensive patients, this is not true for patients with a normal clinic BP. The day-time ambulatory BP (125.5/ 77.2) was identical to the clinic BP (125.3/ 76.5) in 137 normoalbuminuric and normotensive (clinic BP< 149/90 mmHg) type 1 diabetic patients (Table 2) [135]. If the goal for clinic BP in a normoalbuminuric diabetic patients without end organ damage is < 130/85 or < 130/80 mmHg, a similar value can be proposed as a goal for the day time ambulatory BP. The recommendations of the British Hypertension Society [132] that a clinic BP goal < 140/80 mmHg corresponds to day time BP goal < 130/75 mmHg is not scientifically based and leads to unjustified statements concerning the usefulness of ambulatory monitoring [136,137].

Table 2: BP for 137 normotensive and normoalbuminuric type 1 diabetic patients [135]

Mean BP ± SD (systolic/diastolic)

90, 95 percentile (systolic/diastolic)

Clinic BP

(auscultatory, Hawskley, mmHg)

117.4 ±10.0/ 77.8 ±7.2

132/87, 135/89

Clinic BP

(oscillometric, Spacelabs, mmHg)

125.3 ±9.6/ 76.5 ±7.0

139/85, 144/86

Day-time AMBP

(oscillometric, Spacelabs, mmHg)

125.7 ± 8.1/ 77.2 ± 5.7

137/85, 140/87

Night-time AMBP (oscillometric, Spacelabs mmHg)

110.8 ±8.2/ 63.1 ±6.2

122/71, 125/74

Night/day ratio

0.88 ±0.05/ 0.82 ±0.07

0.95/0.90, 0.97/0.94

24-hour AMBP

(oscillometric, Spacelabs mmHg)

120.8 ±7.5/ 72.6 ±5.4

131/80, 134/82

The guidelines will doubtless need corrections based on future studies, which ideally should relate ambulatory BP to end organ damage and to clinical events in antihypertensive drug trials. The clinical value of large-scale implementation of ambulatory BP monitoring has never been investigated. However, it seems wise to hesitate with respect to antihypertensive drug treatment of normoalbuminuric diabetic patients (without any other signs of organ damage) with white coat hypertension. The value of targeting antihypertensive drug regimen towards high night BP is unexplored.

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