26th June 2023

Hypertension and the kidney

Hypertensive nephrosclerosis

Hypertension and renal disease are closely linked; renal dysfunction can develop as a result of chronic hypertension, however, hypertension can also be the result of renal disease. In some cases it can be challenging to differentiate which came first. In benign essential hypertension, arteriosclerosis of major renal arteries occurs. This change is known as nephrosclerosis. Deterioration in renal function accompanies this along with a reduction in the size of both kidneys, which may be asymmetrical if one renal artery is involved more than the other.

Patients with high blood pressure and normal renal function blood tests have a significant reduction in the number of nephrons in each kidney. To compensate for this, there is enlargement of the remaining glomeruli due to hyperfiltration. Microscopic (non-nephrotic range) proteinuria and haematuria occur, as does progressive uraemia.

If treatment of hypertension is initiated before CKD has developed, then there is good prognosis for the preservation of renal function. Patients with CKD should have a blood pressure target of less than 140/90 mmHg for a clinic reading and less than 135/85mmHg for a home or ambulatory blood pressure measurement.

Renal hypertension

Hypertension secondary to renal disease itself can be caused by conditions such as renal artery stenosis, chronic glomerulonephritis, bilateral reflux nephropathy or polycystic disease. There are two main mechanisms which are responsible for the increase in blood pressure:

1.   Activation of the renin-angiotensin-aldosterone (RAAS) system
2.   Retention of salt and water

If the renal disease in question is cortical in nature, such as in glomerulonephritis, hypertension occurs earlier, is more common, and tends to be more severe. This leads to an increase in blood volume and therefore blood pressure. Tight control of blood pressure is necessary to prevent further deterioration in renal function, and there is good evidence that ACE inhibitor treatment offers significant renal protection.