Most patients with hypertension are asymptomatic. The diagnosis is suggested in the emergency department when vital signs are routinely checked. Hypertension is defined as a systolic blood pressure (BP) greater than 140 mm Hg or a diastolic pressure greater than 90 mm Hg. A diagnosis of hypertension is established based on the average of at least two properly measured, seated BP readings on each of two or more office visits. The importance of diagnosing an individual as hypertensive rests on the observation made in multiple studies that cardiovascular and cerebrovascular mortality and morbidity correlate directly with the degree of BP elevation over time. Studies indicate that treatment of patients with even mild hypertension (i.e., diastolic pressures between 90 and 105 mm Hg) may be quite beneficial, although some experts do not agree that there is significant benefit in treating patients with borderline hypertension. Elevated BP readings in the emergency department should be repeated and addressed appropriately.

One concern with elevated BP in the emergency department is that pain or stress may transiently elevate BP. Asymptomatic patients with systolic BP greater than 140 mm Hg or diastolic BP greater than 90 mm Hg should be referred for follow-up of possible hypertension.

Most patients with hypertension will be defined as having essential hypertension in that no secondary cause is discovered after a detailed investigation. However, given that as many as 10% of patients will have a secondary cause, screening for these potential causes is important. Diseases and conditions that cause hypertension include renal disease and renal artery stenosis, primary hyperaldosteronism, Cushing syndrome, pheochromocytoma, coarctation of the aorta, estrogen use, pregnancy, medications (especially NSAIDs), various street drugs, hypercalcemia from any cause, neurologic diseases with increased intracranial pressure (ICP), acromegaly, and hypothyroidism or hyperthyroidism. Evaluation is focused on identifying cardiovascular, renal, neurologic, and ophthalmic end organ damage.

BP should be determined in both arms. Funduscopy should be performed to detect the presence of retinopathic changes consistent with acute or long-standing hypertension. An S₄ or signs of congestive heart failure should be noted as well. Bruits should be sought in the abdomen.

Diagnostic screening tests for evidence of target organ damage in an asymptomatic patient may include urinalysis, serum creatinine level, electrocardiogram, and chest X-ray. Of these, urine dipstick is the only diagnostic ED test with evidence to support its routine use.