Pulse oximeters are being used here to monitor Covid-19 patients for clinical deterioration and for early detection of complications that may arise.
This is particularly useful for those who face increasing difficulty in absorbing sufficient oxygen for their needs, before other clinical symptoms manifest, the Ministry of Health (MOH) said.
Such devices are also being used in the dormitories for infected migrant workers so that they can monitor their own health status and reach out for medical assistance if needed.
There is no evidence, however, to support broad-based community use of pulse oximeters in asymptomatic people for the purpose of identifying individuals for Covid-19 testing, a spokesman told The Straits Times. She said the oximeters must be used properly for accurate measurements of the degree of oxygen saturation in the blood.
Improper application of pulse oximeters can lead to false readings, the MOH said, adding that low oxygen saturation readings are also not specific only to Covid-19 infection as many medical conditions, including asthma and heart disease, can also affect blood oxygen level.
While the demand for pulse oximeters is on the rise here, a comprehensive clinical assessment that includes checking the patient's contact history, as well as other symptoms such as fever or cough, is important for diagnosis, medical experts said.
Some experts in the United States have called for these to be deployed to detect coronavirus patients with "silent hypoxia", where patients' blood oxygen levels are extraordinarily low even if they are not struggling to breathe. This might allow for earlier medical treatment and prevent deaths.
Recently, the Temasek Foundation, which has contributed oximeters to the migrant worker community, has also supported their use. It has run community service advertisements saying it can be useful to learn how to use a pulse oximeter as a Covid-19 patient may not know if he has "silent pneumonia".
Patients should consult a doctor if the oximeter reading falls below 95 per cent, it said.
Ms Woon Saet Nyoon, chief executive of Temasek Foundation Cares, which runs community initiatives under Temasek Foundation, stressed the importance of monitoring for Covid-19 symptoms.
She added that "besides the common symptoms, it is also useful for us to learn how to use an oximeter, which can help provide early detection if not enough oxygen is getting to our body's vital organs".
Medical suppliers have reported an increase in inquiries and demand for such oximeters lately.
A spokesman for Hoffmann Medical Singapore said sales have risen by at least 70 per cent since February.
Mr Ron Loh, owner of Rehab King, an eldercare products store, said oximeters have been "flying off the shelves" since the start of this month. "We used to sell four or five oximeters a month, but now we are selling at least five a day," he said.
The price of oximeters can range from as low as about $20 to a few hundred dollars.
But Associate Professor Hsu Li Yang, programme leader for infectious diseases at the National University of Singapore's Saw Swee Hock School of Public Health, said having low oxygen saturation as the only sign of Covid-19 is extremely rare. "For the vast majority of people, there is no need to buy a pulse oximeter," he said.
While people's bodies and immune systems may sometimes react differently, leading to less common symptoms, most people do develop the more common symptoms after infection such as cough, fever, muscle aches and breathing difficulties, he added.
Normal pulse oximeter readings usually range from 95 to 100 per cent. But Prof Hsu said it is important to establish the baseline oxygen saturation for the individual in order to determine if one has an abnormal reading.
For instance, while the baseline oxygen saturation for most young and healthy people would be well above 95 per cent, others with underlying lung disease or who are obese may already have a baseline oxygen saturation that falls below 95 per cent, he said.
Professor Shiv Pillai, a medicine and health sciences and technology professor at Harvard Medical School, noted that oxygen saturation will drop only when the disease becomes rampant in the lungs.
Dr Jim Teo, a respiratory physician at The Respiratory Practice, said: "If oximeters are not used properly, they can create unnecessary alarm or even provide a false sense of security. Visiting a doctor will allow for a holistic check-up as oximeter readings alone are not indicative of Covid-19."
Other doctors suggested oximeters might be more suited as a tracking device than a diagnostic one.
Dr Wong Tien Hua, a family physician at Mutual Healthcare Medical Clinic, noted that such devices might be more useful for workers in dormitories who have tested positive, as compared with general use at home, as it can help healthcare workers to detect earlier if the workers' condition has deteriorated.
Some 8,000 pulse oximeters have been distributed to foreign workers in dormitories who have tested positive for Covid-19. A further 12,000 will be given out, Manpower Minister Josephine Teo said on Sunday.
Dr Wong said healthcare workers stationed at the dormitories can also help to verify abnormal oximeter readings on the spot, he added.
"There may also be language barriers, so workers may not be able to tell (staff) that they are feeling breathless. But the oximeter can help to detect if their lung function has been compromised."
• Additional reporting by Charmaine Ng