The diagnosis of White Coat Hypertension or the White Coat effect for treated patients depends on comparing the clinic pressures and out-of-office pressures. For a valid comparison, pressures measured in both settings should be accurate, but representative of each setting. Only one or two pressures are taken at a usual clinic visit by varying personnel (medical assistant, nurse, or physician) on either arm and in the sitting position. The limitations for clinic pressure have been amply documented [22] and include inaccurate devices, incorrect cuff size, lack of training and observer bias if auscultation is used rather than a device [23]. Since the virtual disappearance of mercury column sphygmomanometers due to concern about contamination, many clinics now use either an aneroid sphygmomanometer with auscultation or a device that inflates the cuff has a sensor in the cuff and displays pressure. In general, pressures measured by the physician are higher than those measured by trained nurses, resulting in a greater likelihood of WCH or WCE when out-of-office measurements are obtained for comparison [22].

Measuring more blood pressures with an accurate device at the clinic visit can reduce the chance of a false positive diagnosis of WCH or WCE. Bias is eliminated. Several approaches have been explored. Patients referred to the Mayo Clinic have been evaluated by a 6-h recording using the SpaceLabs ambulatory blood pressure monitor. There was excellent correlation with measurements made by trained nurses for systolic pressure. Diastolic pressures were about 7 mmHg higher for 6 h average compared to nurse measurements. Results were not compared with either out-of-office measurement by ABPM or HBPM [24].

Extensive studies have been reported for use of the BpTru device for clinic pressures. The BpTru consists of a cuff with pressure detector by oscillometry, inflation pump, and recording software that uses a programmed sequence of pressure measurements, then calculates the average pressures. The first measurement is discarded. Average pressures are then calculated from the following five measurements, usually taken at 1–2 min intervals [25]. In a series of 400 patients evaluated by both daytime ABPM and in clinic by BpTru, average systolic and diastolic pressures were very similar and highly correlated: systolic pressure r = 0.640 and diastolic pressure r = 0.693 for comparison between daytime ABPM and BpTru using 1 min intervals. However, the absolute differences for individuals were often >5 mmHg for systolic or diastolic pressure and nearly 20 % had differences of >10 mmHg. The widely available Omron device has been compared to the BpTru for clinic assessment. Both devices give very similar systolic and diastolic pressure measurements when taken at 1-min intervals. When taken at 2-min intervals, systolic pressures were similar, but the average diastolic pressures were higher for the BpTru device [26].

The generally accepted “gold standard” for measuring out-of-office pressure is non-invasive 24-h ambulatory blood pressure monitoring. Several accurate and well-validated devices for this purpose are now available. Protocols for use of ABPM have been described in guidelines and recommend measurements every 15–20 min during the day and every 30 min during the night. Use of ABPM requires well-trained staff, patient education to minimize errors (i.e., exercise), and computers for programing the monitors, collecting stored results and preparing reports. In general, patients go to a practice or station for placement of monitors and return the devices after a day of monitoring. This results in some degree of inconvenience in requiring two visits per ABPM determination. The costs for resources and personnel to maintain and ABPM program are small, by Western standards, but steep for developing nations. At present, US Medicare and other insurance providers pay for ambulatory blood pressure monitoring when the diagnosis of WCH is suspected.

Home blood pressure monitoring (HBPM) is most accurate and reliable when automated devices are used (i.e., Omron et al.). There is very good correlation between HBPM and daytime ABPM. Devices must be checked for accuracy. Patients need to be trained for use of the devices, recording of results (if devices don’t have memory), and transmission of results as data sheets or by telemetry (an increasing trend). Feedback and counseling can be done by phone or e-mail (security necessary) so that there is less need for clinic visits. An average of 10–20 home measurements is needed for comparison with clinic pressures to determine presence or absence of WCH/WCE [27]. Most insurance providers don’t support purchase of HBPM devices. Prices are in the range of $70–100 for devices with automatic inflation and memory for storing results. Devices are widely available in pharmacies and medical supply stores. Combining HBPM with transmission of results directly to the provider by telemetry is now available in some programs. One advantage for HBPM with telemetry for treated patients is that patients can evaluate the effect of treatment and even participate in drug titration during follow-up care, reducing unnecessary medication that might be prescribed if only office pressures were available [28–31].