Hypertension, or high blood pressure, that results from kidney disease is known as renal hypertension. It is a form of secondary hypertension, meaning it is a direct consequence of a kidney-related medical issue. This is different from primary hypertension, which has no single identifiable cause. Identifying and addressing the underlying kidney problem is the focus, as it can lead to better blood pressure control.
How Kidneys Regulate Blood Pressure
The kidneys are central to maintaining stable blood pressure through two mechanisms. The first involves managing the body’s fluid and sodium levels. By controlling the amount of water and salt excreted in urine, the kidneys regulate blood volume. When blood volume increases, so does pressure, and by excreting excess fluid, the kidneys can lower this pressure.
The second mechanism is the Renin-Angiotensin-Aldosterone System (RAAS). When the kidneys sense a drop in blood flow, they release an enzyme called renin. Renin initiates a cascade that converts a protein called angiotensinogen into angiotensin I. This substance is then converted into the active hormone, angiotensin II.
Angiotensin II has a powerful effect on blood pressure. It directly causes small arteries to constrict, which immediately increases blood pressure. It also signals the adrenal glands to release aldosterone. Aldosterone instructs the kidneys to retain more sodium and water, further increasing blood volume and sustaining higher blood pressure.
Renal Conditions That Lead to Hypertension
Kidney disorders can lead to secondary hypertension by affecting blood flow to the kidneys or by damaging kidney tissue. One condition that affects blood flow is renal artery stenosis, which is the narrowing of one or both arteries that supply blood to the kidneys.
This narrowing is most often caused by atherosclerosis, the same buildup of fatty plaques that affects heart arteries. In younger individuals, a condition called fibromuscular dysplasia can be the cause. The reduced blood flow tricks the kidney into believing the body’s blood pressure is low, which triggers an excessive release of renin, activating the RAAS and driving blood pressure to high levels.
Diseases that directly damage kidney tissue also cause hypertension. Chronic Kidney Disease (CKD) impairs the ability to filter blood and manage fluid, leading to fluid retention and an overactive RAAS. Similarly, glomerulonephritis, an inflammation of the kidney’s filtering units, compromises their function and causes blood pressure to rise. Polycystic kidney disease (PKD) is an inherited disorder where cysts enlarge and disrupt normal kidney structure, which also impairs function and activates the RAAS.
Identifying the Underlying Renal Cause
Diagnosis begins when signs raise suspicion, such as hypertension resistant to multiple medications or a sudden worsening of controlled blood pressure. Other signs include the onset of high blood pressure in a person under 30 or over 55. A physician may also listen for a bruit over the abdomen, which indicates turbulent blood flow in a narrowed renal artery.
Initial investigations involve lab tests to assess kidney function. Blood tests measure waste products like creatinine and blood urea nitrogen (BUN), and the creatinine level is used to calculate the estimated glomerular filtration rate (eGFR). A urinalysis is also performed to check for protein or blood, which can signal kidney damage.
If initial tests suggest a kidney issue, imaging studies are the next step to view the kidneys and their blood supply. A renal Doppler ultrasound is a non-invasive test often used first, as it can visualize blood flow through the renal arteries to detect narrowing. For more detailed images, a computed tomographic angiogram (CTA) or a magnetic resonance angiogram (MRA) may be ordered. The definitive test is a renal arteriogram, an invasive procedure that uses dye for precise imaging.
Management and Treatment Strategies
Managing hypertension from renal disorders focuses on controlling blood pressure and addressing the specific kidney problem. If renal artery stenosis is the cause, a procedure to restore blood flow may be recommended.
One procedure is percutaneous transluminal angioplasty, where a small balloon is inflated inside the narrowed artery to widen it. A stent—a small, expandable mesh tube—is often placed to keep the artery open. In complex cases, surgical revascularization, or a renal bypass, might be performed to create a new path for blood to flow to the kidney.
Alongside treating the root cause, controlling blood pressure with medication is fundamental. Because the RAAS is often overactive, medications that target this system are frequently used. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs) are first-line treatments because they directly counteract the hormonal cascade that raises blood pressure.
These medications relax blood vessels and help the kidneys excrete more sodium and water. Other blood pressure medications, like calcium channel blockers or diuretics, may be used in combination for optimal control. Successful treatment of the renal issue can improve or even resolve the hypertension, reducing the need for long-term medication.