The post COVID-19 functional status scale has been adopted in 100+ clinics or research projects. I think this is a great testimony to the power that science and collaborations brings to this pandemic. But with a new tool comes also a way of thinking that is perhaps standard in stroke research but perhaps not so obvious outside that field. I might have underestimated that when we proposed the PCFS. To provide some guidance, just think about this. Know, be consistent and open about when, what and who you count when assessing the PCFS in your clinic or cohort. And yeah, do not forget the dead.
- WHEN: when you count the PCFS in your patients is just perhaps one of the most important aspects of the PCFS when you want to make use of all its potential. When you assess the PCFS must be standardized. It would be best if it were standardized between studies or clinics (e.g. @discharge and 4 & 8 weeks thereafter, as we suggest in the original proposal) but this might not be suitable in all instances. If you can’t keep this, try at least to standardize the moment of assessing the PCFS constant, with a narrow time window, within one data collection. As COVID-19 patients are likely to improve overtime, it matters when who is interviewed. Irrespective of whether you were able to keep the time window as tight as possible, make sure to report the details on the window in your papers. Better even – share the data.
- WHO: If you only assess the PCFS in the survivors of COVID-19, you build in a selection. And when there is a selection, selection bias is around the corner. The clearest example comes from the comparison of those patients admitted to the ICU vs those who were not. If we do not count the dead in the ICU population, but we do in the other group, it might well be that the PCFS distribution amongst those with the PCFS assessment is in favor of being in the ICU group. All patients who enter the cohort need a PCFS assessment, also the dead. Again, whatever you did, make sure you describe who were assessed and who weren’t in your methods and results of your papers.
- HOW: in our proposal we give the option to do an interview or a self-assessment questionnaire. We don’t have enough evidence to support one over the other. We think interviews provide a little more depth, but the bottom line is that professionals should choose the one that fits their needs the best. Both outcome assessments methods will provide different scores and that is just fine, as long as it is clear to others what you actually did. But be aware: mixing two types in one study or cohort can bring some bias – see above. Make sure you provide an adequate description of what you did, even when you follow the proposed methods in our manual – the PCFS is not completely standardized in the literature, so you need to bring your colleagues up to speed.
In a clinical setting it is easy to take these three variables into account when discussing a single patient. After all, you only need to put the PCFS in the context of one individual. At most, you need to consider the PCFS measured over multiple time points. But if you want to learn from your experiences, it is best to make the assessment as standardized as possible. It will help to interpret the data of an individual patients quicker, see patterns within and perhaps between patients, and as a final kicker, might make it possible to do some research with that valuable data.