Investigation for hypertension remains a contentious issue in so much as who should be investigated. It is my personal practice to investigate young people with the onset of hypertension or more elderly people if hypertension control is suddenly lost. I usually investigate all patients in whom good blood pressure control cannot be achieved with three medications.
- UEC’s and U/A.
- Renal Ultrasound. This will show you renal structure and may show asymmetrical kidneys or previous renal scarring.
- Renal Dopplers. Renal artery stenosis is one of the causes of hypertension in the young (fibromuscular dysplasia) and in the elderly (atherosclerotic renal artery stenosis.
- 24 hour creatinine clearance. This is a much more sensitive indicator of true renal function rather than UEC’s and is especially helpful in the elderly.
- Serum renin to aldosterone ratio. This is a routine random blood test which is very helpful for the screening of Conn’s syndrome. It is nice to perform this test early before the patient is on multiple medications as it is effected by most drugs other than calcium channel blockers.
- 24 hour catecholamines. Phaeochromocytoma is a rare but definite cause of hypertension.
Other investigations that are often helpful include 24 hour blood pressure monitoring which often shows a lack of diurnal variation. If I remain suspicious of renal artery stenosis then renal perfusion scanning with deferential GFR and ACE inhibitor challenge is useful especially in patients in whom poor ultrasound images are obtained. The gold standard test for renal artery stenosis is digital substruction angiography which can be performed at the same time as cardiac catheterisation and is frequently done so in patients undergoing angiography who happen to have a secondary diagnosis of hypertension.
Please note that the above investigations are a guide only and may need to be modified for the individual patient.