diagnostic tests for obesity hypoventilation syndrome (OHS)

Last edited 09/2021 and last reviewed 10/2021

Diagnostic tests for obesity hypoventilation syndrome (OHS)

Diagnosing OHS and assessing ventilatory failure

• consider measuring serum venous bicarbonate as a preliminary test if the pre-test probability of OHS is low. If bicarbonate levels are below 27 mmol/litre, OHS is unlikely.
• measure arterial or arterialised capillary blood gases when the person with suspected OHS is awake, to diagnose OHS and assess the extent of chronic ventilatory failure
• do not delay treatment for acute ventilatory failure to carry out further investigations for OHS

Diagnosing the presence of OSAHS (obstructive sleep apnoea/hypopnoea syndrome) or nocturnal hypoventilation in people with OHS

• offer respiratory polygraphy, either in hospital or at home, to determine the presence of OSAHS in people with suspected OHS
• consider adding transcutaneous CO2 monitoring during sleep to respiratory polygraphy in people with suspected OHS to determine the extent of nocturnal hypoventilation and provide additional information to guide treatment
• do not use oximetry alone to determine the presence of OSAHS in people with OHS

Reference:

• NICE (August 2021). Obstructive sleep apnoea/hypopnoea syndrome and obesity hypoventilation syndrome in over 16s