High blood pressure, or hypertension, happens when the pressure of blood in the body is too high.
This is dangerous, because it places extra strain on the blood vessels, which can lead to heart attacks and strokes.
It’s very rare to experience noticeable symptoms if you have high blood pressure. More than a quarter of adults in the UK have high blood pressure, many of whom won’t realise it, according to the NHS.
However, when blood pressure reaches severely high levels, symptoms can appear.
When blood pressure is extremely high, this is known as malignant hypertension, or a hypertensive crisis, and should be treated as a medical emergency.
Malignant hypertension happens when blood pressure spikes suddenly and extremely, and according to medical website Healthline, this could cause a reduced urine output.
A reduced urine output is considered to be a urinary output of less than 400 millilitres over the course of 24 hours.
This could be a sign of many other things, such as kidney disease or dehydration, so it’s important to see a doctor if you experience it.
If present with other symptoms of malignant hypertension, a reduced urine output could signify a hypertensive crisis.
Other symptoms of malignant hypertension include severe headaches, vision problems, chest pain, nosebleeds, blood in the urine, and nausea and vomiting.
According to the NHS, normal blood pressure is considered to be between 90/60mmHg and 120/80mmHg.
High blood pressure is considered to be 140/90mmHg or higher.
Malignant hypertension is considered to be above 180/120mmHg.
If blood pressure is that high during a blood pressure check, Healthline advises waiting a few minutes before measuring it again to check the first reading was accurate.
If the second blood pressure reading is still that high, call the emergency services immediately.
Malignant hypertension develops rapidly and is often a result of high blood pressure not being controlled properly.
For example, if you are taking medication for high blood pressure but miss doses, you could be at risk of developing an hypertensive crisis.
Malignant hypertension is dangerous because it can result in fluid in the lungs, brain swelling or bleeding, and strokes.
As high blood pressure in general rarely has symptoms, the NHS advises getting blood pressure checked regularly by a GP.
“All adults over 40 are advised to have their blood pressure checked at least every five years,” said the NHS.
“Getting this done is easy and could save your life.”