Throughout the use of the PG-SGA or the Pt-Global app/web tool, it is important to think of the patient in terms of whether the patient is anabolic or catabolic. Lean tissue/non-fluid weight increase tend to represent anabolism (positive nitrogen balance) whereas lean tissue/non-fluid weight decrease may represent catabolism in an ill patient. Weight and physical examination are surrogate markers for anabolism or catabolism.
If a patient is anabolic, she will likely improve weight (slow/stop weight loss or increase weight) whereas if the patient is catabolic her weight may decrease and physical examination, particularly of muscle may deteriorate. But the best practical clinical approach to address anabolic competence (positive nitrogen balance) is a 24 hour urinary urea nitrogen (UUN or output) combined with calculation of protein nitrogen intake. If more nitrogen out than in, the patient is in negative nitrogen balance; if more nitrogen in than out, the patient is in positive nitrogen balance. One can only be anabolic in the face of positive nitrogen balance.
Practical consideration: For inpatients (and often for outpatients), Sunday is usually the best day to collect the urine for UUN, because  Sundays are characterized by fewer tests, fewer procedures, fewer activities, and collections tend to be much easier on patient and staff.
The other benefit of collecting the UUN is that one has a very specific target amount of nitrogen (protein) that should be added to intake, to convert from catabolism to anabolism. Sometimes patients can be much more catabolic than one realizes and with the target increase one can accomplish this conversation in a much shorter and precise time frame.