Table 6: Inaccuracies in the Measurement of Blood Pressure

Table 6:
Inaccuracies in the Measurement of Blood Pressure
Error	Result	Solution
Inaccuracy Resulting from Improper Instruments
Inaccuracy of the manometer	Readings may be over or underestimates of the true blood pressure.	Mercury manometers are the preferred devices. Aneroid manometers must be compared against a mercury device before use. Any discrepancy of 3 mm Hg or more requires calibration.
Cuff too small	Cuff bladders too narrow or too small for the limb will yield artifactually high readings.	Use the proper cuff size as estimated by Tables 4 and 5.
Cuff too large	Cuff bladders too wide or large for the limb may yield artifactually low readings.	Use the proper cuff size as estimated by Tables 4 and 5.
Inaccuracy Resulting from Observer Traits
Terminal digit bias	Most values for blood pressure end in 0 or 5.	Retraining. Proper blood pressure measurements should be recorded within 2 mm Hg. Alternatively, use an automated device.
Cuff pressure is released too fast	The blood pressure is underestimated as the pressure is released faster than the corresponding heartbeats occur.	Retraining. Pressure should be released no faster than 2 mm Hg per heartbeat in order to achieve maximal accuracy.
Examiner bias	The blood pressure may be more often recorded at values just over or just under diagnostic cut-off, in order to institute or avoid institution of an intervention .	Retraining. Alternatively, use of an automated device.
Soft Korotkoff's sounds	Difficulty hearing distinct cut-offs.	Subject elevates arm and opens and closes fist several times; cuff is then applied, arm is lowered, and auscultation is reattempted.
Inaccuracy Inherent in the Technique
White-coat hypertension	Some patients have normal blood pressure when measured at home but higher readings when measured in the clinical setting.	This is a group for whom ambulatory or home blood pressure readings may be the preferred method of making the diagnosis and following the effects of treatment.
Intra-arm differences	Studies have documented pressure differences of >10 mm Hg between the arms of hypertensive patients.	Initially, measure blood pressure in both arms, and use the arm with the higher measurements subsequently.

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