Understanding Pulse Oximeter Readings

A pulse oximeter shows two numbers, and sometimes a moving bar or wave. They look simple, but interpreting them correctly means knowing what is normal, how precise the device is and which changes matter. This guide explains the display and what to do with the information. For measuring technique, see how to use a pulse oximeter.

The two main numbers

SpO2: oxygen saturation

Shown as a percentage, often labeled %SpO2. Red blood cells carry oxygen from the lungs to the rest of the body. SpO2 estimates how much of that carrying capacity is in use. A reading of 97% means the blood is carrying about 97 percent of the oxygen it could.

PR: pulse rate

Shown in beats per minute, labeled PR or with a heart symbol. It tells you how fast your heart is beating at that moment.

Other display elements

• Pulse bar or waveform: rises and falls with each heartbeat. A regular, even pattern suggests the device has a good signal. An erratic pattern usually means movement or poor contact.
• Perfusion index (PI): on some devices, an indicator of pulse strength at the fingertip. A very low value suggests a weak signal and a less reliable reading.
• Battery indicator.

What is a normal SpO2?

MedlinePlus states that a normal oxygen saturation level ranges between 95% and 100%.

Some people have a lower usual level, particularly those with long-term lung conditions. If you have such a condition, your doctor should tell you what range to expect and what reading should prompt a call. Altitude also lowers oxygen saturation.

When a reading is low

MedlinePlus gives this guidance for home monitoring:

• 92% or lower: contact your provider.
• 88% or lower: seek immediate medical attention.

Follow any different instructions your own doctor has given you. Before acting on a single low number when you feel well, check the basics: warm the hand, sit still, reseat the device and measure again. If the reading remains low, treat it as real.

If you have symptoms such as shortness of breath, chest pain, bluish lips or confusion, seek urgent help whatever the device shows.

How accurate are the readings?

MedlinePlus notes that pulse oximetry results may be 2% to 4% higher or lower than your actual blood oxygen level. A displayed 94% could therefore reflect a true value a few points either side.

The FDA lists several factors that affect accuracy:

• poor circulation;
• skin pigmentation;
• skin thickness;
• skin temperature;
• current tobacco use;
• fingernail polish.

The FDA has also highlighted concerns that pulse oximeters may be less accurate in people with darker skin pigmentation. This makes it especially important not to be falsely reassured by a normal reading when symptoms suggest a problem.

A blood test called an arterial blood gas, performed in a hospital or clinic, measures oxygen directly and is used when precision is needed.

Why trends matter

Because of this margin of error, the pattern over time is more informative than any single reading.

• Measure at the same times each day, at rest, using the same finger.
• Write down each result with the date and time.
• Look for a sustained fall compared with your usual level.
• Report a downward trend to your doctor, even if the numbers are still within the normal range.

Understanding pulse rate

MedlinePlus gives the normal resting heart rate for adults, and children aged 10 and older, as 60 to 100 beats per minute. Well-trained athletes may have a resting rate of 40 to 60.

Pulse rate rises with:

• activity;
• fever;
• pain, anxiety or stress;
• caffeine and some medicines;
• dehydration.

Talk to your doctor if your resting pulse is consistently above 100 or below 60 and you are not an athlete, or if it feels irregular. A fingertip oximeter cannot diagnose a heart rhythm problem.

Readings that do not make sense

The numbers keep jumping

Usually movement, a cold finger or a loose fit. Rest your hand on a table and wait.

The reading is very low but you feel fine

Often a poor signal. Warm your hand, remove nail polish, try another finger and replace the batteries. If it stays low, seek advice.

No reading at all

The finger may not be fully inserted, or circulation to the finger is poor.

The pulse on the display differs from the pulse you count

The device is probably not detecting each beat. Reposition it.

Things an oximeter does not tell you

• The amount of carbon dioxide in your blood
• How hard you are working to breathe
• Whether you have an infection
• The cause of a low reading

It also reads falsely high in carbon monoxide poisoning. If carbon monoxide exposure is possible, get out of the building and call 911, regardless of the number.

Keeping a record

Record:

• date and time;
• SpO2;
• pulse rate;
• whether you were resting or active;
• oxygen use, if any;
• symptoms.

Bring the record to appointments. It gives your doctor far more than memory can.

Who benefits from home readings?

Home monitoring is most useful when a healthcare professional has recommended it, for example for certain lung or heart conditions, and has explained what to do with the results. For healthy people without symptoms, routine checking adds little and can cause needless worry.

Call 911 or seek emergency care for

• severe shortness of breath or struggling to breathe;
• bluish or gray lips, face or nails;
• chest pain or pressure;
• confusion or difficulty staying awake;
• a reading of 88% or lower that does not improve after you recheck.

About our device

Our Fingertip Pulse Oximeter displays SpO2 and pulse rate. Read the instructions, and ask your doctor what readings are expected for you.

The bottom line

Read SpO2 and pulse rate together, allow for the device’s margin of error, follow trends and let symptoms take priority. Find monitoring devices in our medical supplies department.

Sources

1. MedlinePlus. Pulse Oximetry.
2. U.S. Food and Drug Administration. Pulse Oximeters.
3. MedlinePlus. Pulse.