How is my oxygen level measured?

Usually with pulse oximetry — a painless clip on a finger or earlobe — and a blood gas test, where a small sample is taken from an artery at the wrist or the earlobe for a more accurate reading. These show whether your oxygen is genuinely low enough to need treatment.

Why is oxygen assessed when I am well, not during a flare-up?

Because your oxygen dips temporarily when you are unwell, so a reading taken during a chest infection would not reflect your true, ongoing need. Assessing when stable makes sure the prescription matches your everyday level.

Do I really have to use oxygen for so many hours?

For long-term oxygen therapy to work, it must be used for the prescribed hours — often at least around fifteen a day including sleep. Using it for fewer hours reduces the benefit. The exact number is set by your team.

Do I have to stop smoking to get home oxygen?

Usually yes. Oxygen is far less beneficial if you keep smoking, and — critically — smoking near oxygen is extremely dangerous and has caused severe burns and deaths. This includes vaping. Your team can refer you to stop-smoking support.

Home Oxygen Assessment & Prescription

Q: Can I just buy home oxygen?

No. Home oxygen is a prescribed medical treatment given only after a proper assessment. The NHS warns that using oxygen without a prescription can be dangerous and could damage the brain, heart and lungs. Both too little and too much oxygen can harm, so it must be prescribed for you.

Written & reviewed by the BestDoctors.sg editorial team · Last updated 28 Aug 2026 · General information, not medical advice

Home oxygen is a prescribed medical treatment, and getting it right starts with a proper assessment. Rather than being something you can simply buy and switch on, oxygen is measured, matched and prescribed to your individual need — and reviewed over time. Understanding how you are assessed, why it is done when you are well rather than during a flare-up, and why the settings are fixed for you helps you get the full benefit safely. This guide explains the process.

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In a medical emergency, or for severe or sudden symptoms such as breathing difficulty, chest pain, fainting or stroke signs, call 995 immediately.

This is general information and does not replace your team’s advice. Oxygen is prescribed for low blood oxygen, not breathlessness on its own, and the flow rate is set by your team — never change it yourself. Call 995 for severe breathlessness, blue lips, or new drowsiness or confusion.

Oxygen is prescribed, not bought

Home oxygen is a prescribed treatment given only after a proper clinical assessment — it is not something to buy over the counter or fit yourself. The NHS warns that buying and using oxygen without a prescription can be dangerous and could damage the brain, heart and lungs. The reason is that both too little and too much oxygen can cause harm, so the right amount has to be worked out and prescribed for you, and then delivered by properly installed equipment.

How you are assessed

Assessment measures how much oxygen is in your blood. This usually starts with pulse oximetry — a painless clip on a finger or earlobe that estimates your oxygen level — and includes a blood gas test, where a small blood sample is taken from an artery at the wrist, or sometimes the earlobe, to give a more accurate reading. These measurements show whether your oxygen is genuinely low enough to need treatment, and if so how much you need. The finger test is quick and can be repeated easily, while the blood test gives the fuller picture that a prescription is based on.

Why assessment when stable matters

Timing matters. Oxygen assessment is done when you are stable and well — not during a chest infection or a flare-up of your condition. That is because your oxygen level dips temporarily when you are unwell, and a reading taken then would not reflect your true, ongoing need. Being assessed when stable makes sure the prescription matches your everyday level, so you are neither under-treated nor given oxygen you do not really need.

Two readings, weeks apart

Before long-term oxygen therapy is confirmed, the blood gas measurement is usually repeated on two separate occasions, a few weeks apart, again while you are stable. This double check avoids starting a long-term treatment on the basis of a single, possibly unrepresentative reading. Your oxygen level can vary from day to day, so two readings taken a few weeks apart give a much more reliable picture than one alone. It can feel like a wait, but it is there to be sure that oxygen is truly the right treatment for you and will genuinely help. Starting long-term oxygen is a significant step, so the team wants to be confident it is the correct one before you begin.

Setting the flow and hours

Your respiratory team sets both the flow rate — how much oxygen you receive — and the number of hours a day to use it, matched to your results. For long-term oxygen therapy to work, it needs to be used for the prescribed hours, often at least around fifteen a day including while you sleep; using it for fewer hours reduces the benefit. Crucially, you must not change the flow rate yourself, as more is not safer and can be harmful.

Stopping smoking

Stopping smoking is usually required before long-term oxygen is prescribed, for two reasons. First, oxygen is far less beneficial if you keep smoking. Second, and just as important, smoking near oxygen is extremely dangerous because oxygen makes fires start and spread fiercely — it has caused severe burns and deaths. This applies to e-cigarettes and vaping too. Your team can refer you to stop-smoking support, and quitting brings benefits well beyond the oxygen itself.

The walk test and follow-up reviews

If portable, ambulatory oxygen is being considered, assessment usually includes a walking test — you walk with and without oxygen while your levels are monitored, to see whether your oxygen drops on exertion and whether portable oxygen helps. After oxygen is started, you will have regular follow-up reviews to check it is still needed, that the prescription is right, and that the equipment is working, because your needs can change over time. These reviews are a normal part of the treatment, not a sign that anything is wrong. In Singapore, your hospital respiratory service arranges this assessment and review, supported by HealthHub’s Airway Programme information.

Sources

Asthma + Lung UK — What is home oxygen therapy: asthmaandlung.org.uk
NHS — Home oxygen treatment: nhs.uk
British Thoracic Society — Quality standards for home oxygen: brit-thoracic.org.uk
North Tees and Hartlepool NHS — Home oxygen therapy: nth.nhs.uk

General information only. This guide supports — but does not replace — the advice of your respiratory team and oxygen supplier, who set your oxygen and tailor it to you. Never change your own oxygen flow rate, and never smoke or allow naked flames near oxygen. Oxygen is prescribed for low blood oxygen, not to relieve breathlessness on its own. Call 995 if breathing becomes severe or does not ease as usual, if the lips or fingertips turn blue, for chest pain, or if the person becomes unusually drowsy, confused or hard to wake (a possible build-up of carbon dioxide from too much oxygen). If you are struggling emotionally, you are not alone — the Samaritans of Singapore (SOS) are on 1767 and mindline.sg on 1771.

Home Oxygen Assessment & Prescription (Singapore)