Health experts are concerned some people self-isolating with Covid-19 aren't getting enough information on how to use a small, potentially life-saving device.

More than 1500 people with Covid-19 are currently isolating at home, many with a pulse oximeter.

The device clips onto your finger and measures your heart rate and the oxygen saturation, or levels, in your blood.

"It does that by shining a light and measuring how much it sort of reflects back," GP spokesperson for the New Zealand Medical Association Dr Vanessa Weenick said.

"Then a number is displayed on the little screen, which shows you percentage. So, in the case of Covid, we're looking to make sure that people's oxygen saturation is higher than 95 percent.

But if it drops below that it is a warning sign, she said.

"It means that the oxygen that's coming into your lungs isn't going through into your blood and often that's because of fluid filling up in your lungs like when people get pneumonia."

Weenick said that would feel like they were starving for oxygen.

"They would feel like they just couldn't get a breath and they might be feeling a little bit lightheaded and woozy."

However, new research out of the United Kingdom shows oximeters can overstate the amount of oxygen present in people with darker skin.

UK Health Secretary Sajid Javid was so concerned, he ordered a review into whether medical devices are equally effective, regardless of the patient's ethnicity.

In New Zealand, Maori and Pasifika make up about 72 percent of the current outbreak.

Clinical lead of the Royal New Zealand College of GPs Dr Bryan Betty said the device is just one tool in monitoring someone with Covid-19.

"It should be used as part of a package of care, that you have a number to ring a doctor or nurse if there's any problems, that there's a daily check-in, or once every two days to check how things are going, to look at the reading and talk about how the patient is feeling.

"That package is really, really important in terms of home isolation."

He said the commonly-used device is the best we have at this point and it can quickly show whether an unwell person's condition is slipping.

Pasifika Medical Association chief executive Debbie Sorensen said expecting people to use medical equipment without proper supervision can be a big ask.

"There's an assumption that clicking on to a YouTube, or a video clip that shows you how to use the device, or reading a sheet of paper, will actually be sufficient to tell people how to use a device, and I don't think that that's always the case.

"Certainly in the Pacific community, we have a number of people who, english is not the first language and so relying on that method isn't that helpful."

Sorensen said the instructions provided with the devices often are not clear and more effort needs to made to explain how to use them.

"I think there needs to be a bit more thought put into how are people communicated with, in terms of discussing with someone on the phone, or perhaps on a video call or WhatsApp, or another kind of video call that we're used to using all the time, so that people can be sure that they know how to use the device and what to do.

"And not just relying on this as their only way of deciding whether they are sick or not."

Dr Weenick said it is crucial people self-isolating know they should call for urgent help, if they feel they need it.

"If they are feeling very unwell, very short of breath and feeling as though they can not get a breath, then that is more important than the number on the machine," she said.

"It is really important that people understand that if they are feeling terrible, and that doesn't seem like the number matches how they are feeling, then they need to get medical attention and not wait for somebody to tell them that it is okay to do that."

A Ministry of Health spokesperson said a person isolating at home with Covid-19 is called regularly to see how they're doing, and most people self-isolating are given a pulse oximeter within 24 hours.

"In most cases, pulse oximeters are used to provide a level of assurance that blood oxygen levels are not decreasing, which may require the need for direct medical attention," they said in a statement.

The spokesperson said everyone who is given the device is provided with a leaflet explaining how to use it.

"Cases are asked to use them three times daily (morning, midday and evening) and record the results. Cases are also asked to check if they are feeling unwell and take note of symptoms.

"Cases are asked to contact their health team if the oxygen level falls below 95 percent or if their heart rate is above 100."

The spokesperson said the health teams that contact people with Covid-19 ask for the pulse oximeter results and record them.

Anyone with Covid-19 that has chest pains or feels short of breath is urged to call an ambulance, they said.