Our systematic review has several limitations. Firstly, we developed a classification of criteria used to define LTOT based on measures of duration or additional criteria. Given the variability and lack of clarity on reporting for some definitions, misclassification could have occurred. However, we minimised misclassification by performing data collection with two independent reviewers. Secondly, since we excluded studies assessing LTOT in surgical settings the results and recommendations drawn from this study may not be applicable for studies assessing LTOT prior or post-surgery. Thirdly, we did not test the performance of different definitions in identifying LTOT users but rather identified those who have been tested to guide future researchers in their choices. Fourthly, we only addressed the completeness of reporting using core items relevant to the operationalisation of LTOT definitions and associated results, identifying key elements that future studies should consider to increase their transparency and reproducibility and did not assess the methodological quality or relevance of included studies.