The CEBM recommend that the assessment of patients with symptoms of Covid-19 should include oximetry

NHSE guidance states certain groups of patients who are symptomatic of Covid-19 should be provided with a pulse oximeter, home monitoring guidance and monitoring texts/check in calls:

• those  >65 years
• or <65 years and clinically extremely vulnerable (CEV)
• or where clinical judgement applies, taking into account multiple additional Covid risk factors

Measurements that require medical review:

NHSE advise patients with an oxygen saturation level of 93 or 94% to seek medical help, and call 999 if oxygen saturations are 92% or less

NHS London Networks advise that patients with oxygen saturations of 93 or 94% receive follow up daily via hot sites or GP to assess change in level of breathless at rest and with usual activity

NHS London Networks advise that if the patient has COPD or Interstitial lung disease you should review their baseline oxygen saturations so that you can grade deterioration accordingly (details on embedded links)

Accuracy of measurements:

The U.S. Food and Drug Administration (FDA) is reviewing evidence suggesting that pulse oximeters may be less accurate in people with darker skin pigmentation. Be aware that multiple factors can affect the accuracy of a pulse oximeter reading, such as poor circulation, skin pigmentation, skin thickness, skin temperature, current tobacco use, and use of fingernail polish. The FDA advise all people to not rely only on a pulse oximeter and to pay attention to other signs or symptoms of low oxygen levels. Changes or trends in measurements may be more meaningful than one single measurement

Exertional desaturation testing:

• Some patients have normal pulse oximetry at rest but their readings deteriorate on exertion
• A positive desaturation test is a fall of 3% or more in pulse oximetry
• Identifying those with exertional desaturation  and escalating their care more promptly could reduce mortality
• The validated 1-minute sit-to-stand test (patient goes from sit to stand as many times as they can) and the unvalidated 40-step test (take 40 steps on a flat surface) are the most appropriate for recommending to patients at home
• They are likely to be specific but not sensitive (that is, a positive test is serious cause for concern but a negative test should not necessarily reassure)
• Neither should be attempted outside a supervised care setting if oximeter reading is <96%

See Also: 

What you need to know to triage and assess suspected cases of Covid-19

24/7 London wide oxygen saturation probe loan service