Study

Red flags

Creatinine

Evidence of renal impairment

Electrolytes (potassium)

Hypokalemia suggesting potential mineralocorticoid excess

Midstream urine

Evidence of proteinuria or hematuria suggesting a renal etiology

Urine PCR or 24-h urine collection for protein

If midstream urine is positive for proteinuria, recommend for baseline and quantitative assessment

Renal ultrasonography with Doppler

If sudden-onset or worsening hypertension, presence of abdominal bruit, resistance to ≥3 drugs, increase in serum creatinine ≥30% after using ACEI/ARB, significant asymmetry (>1.5 cm) in kidney size, recurrent pulmonary edema, significant atherosclerosis, family history of fibromuscular dysplasia, or personal history in another vascular territory

Sleep study

If evidence of sleep apnea in history (headache, nocturnal choking and gasping, early morning fatigue, snoring)

Plasma renin and aldosterone

If evidence of spontaneous hypokalemia (K <3.5 mmol/L) or hypokalemia with diuretics, resistance to ≥3 drugs, incidental adrenal adenoma

24-h urine metanephrines

If severe ≥180/110 mm Hg refractory hypertension, symptoms of catecholamine excess (headaches, palpitations, sweating, panic attacks, orthostatic syncope), hypertension triggered by beta-blockers, history of multiple endocrine neoplasia 2A or 2b, or incidental adrenal mass

TSH

If evidence of hypothyroidism or hyperthyroidism on clinical assessment

a Only undertaken if signs and symptoms present (see Essential Hypertension).