High blood pressure (hypertensionHigh blood pressure.) and chronic kidney disease (CKD) are directly related. The kidneys are involved in the regulation of blood pressure through various mechanisms, such as the production of reninA hormone-like enzyme, generated and stored in the kidneys. If blood pressure drops, it is released from the kidneys and is highly efficient in raising blood pressure...., a hormone-like substance that plays a role in raising blood pressure. However, the kidneys also play an important role in blood pressure by regulating electrolytesElectrolytes are substances that produce an electrically conducting solution when dissolved in water, releasing mineral ions such as sodium, potassium, chloride and calcium. These ions can either be the positively or negatively charged or, combined as a salt, neutral.... (excretion and reabsorption) and maintaining and regulating the amount of water in the body.
This is also known as the heart-kidney axis, meaning that heart and kidney health are closely linked. The gut is also involved, leading to the gut-heart-kidney axis.
How hypertension affects the kidneys
High blood pressure causes hyperfiltration in the kidneys, which means that more substances are excreted than usual. This initially compensates for the failing nephronsNephrone sind die Filtereinheiten der Nieren...., but also causes the sensitive glomeruli to stiffen under the blood pressure (glomerulosclerosis) and eventually die. This creates a vicious cycle of compensation and overload that is also involved in the progression of CKD.
Because high blood pressure also increases the amount of protein excreted in the urine (proteinuriaIncreased protein in urine, leading to loss of protein. Normally, only a very small amount of protein is excreted in the urine. In chronic kidney disease, the amount lost may increase. High blood pressure damages blood vessels in the nephrons making them more permeable and...), it also supports the progression of chronic kidney disease.
In cats, however, it is not clear whether hypertension is a consequence or a cause of CKD. Approximately 20-65% of CKD cats develop hypertension during the course of their disease. This means that there are CKD cats without hypertension. Hypertension is also associated with other diseases such as hyperthyroidism and adrenal gland disease.
Hypertension is known as the “silent killer” because it takes a long time for cats to show symptoms. In addition to the kidneys, high blood pressure can damage other organ systems: bleeding or retinal detachment can occur in the eyes, and damage to the heart and central nervous system can occur. These four organs (kidneys, eyes, heart, brain) are most commonly affected by hypertension.
Effects of high blood pressure on other organ systems
The main symptoms of hypertension can be vision problems: The cat has enlarged pupils, and may also have a prolapsed nictitating membrane. Because her vision is impaired, she will bump into objects. Hypertension can cause the retinaThe layer of nerve cells lining the back wall inside the eye.... to detach, leading to blindness.
Central nervous system problems such as cramps, seizures or loss of balance may be associated with high blood pressure. The risk of stroke is associated with high blood pressure. If headaches occur, cats may show this by pressing their head against walls or objects.
Less obvious are the changes to the heart caused by high blood pressure, which can lead to thickening of the heart wall and impaired heart function.
IRIS Recommendations
In cats with CKD, it is advisable to monitor and control blood pressure to maintain or improve the cat’s quality of life and to slow the progression of CKD by reducing the proteinuria associated with hypertension.
The International Renal Interest Society (IRIS) has published sub-stages and treatment recommendations for high blood pressure. Treatment recommendations generally take into account the risk of organ damage. Treatment for high blood pressure usually improves symptoms and reduces proteinuria.

For moderate hypertension, antihypertensive therapy is recommended if there is a risk of organ damage, for example to the eye. For severe hypertension, antihypertensive medication is always indicated. The goal of treatment is a systolic blood pressure in the range of 150 – 160 mm Hg. In IRIS stage IV, the target blood pressure may be slightly higher because the blood pressure represents the filtration pressure and the minimally functioning kidney will progress more quickly to fatal kidney failure if the blood pressure drops. It is therefore possible that blood levels of creatinineCreatinine is a breakdown product of muscle metabolism. Its blood level is dependent, among many factors, on age, weight, nutritional status and muscle mass. Hence, creatinine levels in the blood vary from individual to individual. Creatinine is continuously excreted in the urine. Increased blood creatinine..., ureaUrea is the nitrogen-containing breakdown product of protein metabolism. The nitrogen from the proteins is converted to ammonia in the liver, which is combined with carbon dioxide to form urea. This is continuously excreted via the kidneys but also via sweat. Urea is one of... and SDMASDMA = Symmetrical Dimethylarginine, which is a degradation product of the amino acid arginine and is excreted solely through the kidneys. SDMA is a highly specific biomarker for kidney function in cats. Read more: SDMA test (blood test)... may increase when antihypertensive medication is taken.