Boris Johnson was admitted to hospital for tests on Sunday night with persistent coronavirus symptoms, 10 days after testing positive. Some estimates suggest that about 5-10% of people with Covid-19 require hospital treatment.

His admission to hospital indicates doctors want to check how his body is responding to the virus, which will probably involve carrying out the following tests:

Ultrasound/CT scans

Imaging of the lungs through ultrasound or CT scans is used to get an indication of how badly the patient’s lungs have been affected. It can show up patches, mainly on the edges of the lungs, which suggest infectious changes. The information can be used to determine whether assistance with breathing is needed and if so to what extent. At the lower end of the scale, oxygen can be provided via a mask, but patients with more serious breathing problems may require a ventilator.

The scans can also show whether pneumonia is catching hold. Dr Bharat Pankhania, senior clinical lecturer at the University of Exeter’s medical school, said it was not possible to determine whether Johnson had pneumonia based solely on his admission to hospital. “It may be just precautionary. If a patient is developing pneumonia, it can get progressively worse very quickly and hence early admission upon the first signs of difficulty with breathing are very important,” he said.

Blood tests

Assessing white blood cell counts will show the response of the prime minister’s immune system to the virus, in other words how effectively his body is fighting the virus. Doctors will be looking for progression of the disease and to establish that he has not entered the second phase, where the immune system goes into overdrive. Tests also assess liver and kidney function for any warning signs. Both of these organs are at risk of damage from coronavirus and a lack of oxygen.

Electocardiagram (ECG)

This measures the electrical activity of the heart to show if it is working normally. Like the liver and kidney, the heart is also at risk from lack of oxygen. Coronavirus has been found to cause problems such as arrhythmia and acute cardiac injury in some patients.