Prealbumin (aka transthyretin) is, like albumin, an acute phase reactant. It is, also like albumin, a negative acute phase reactant because it goes down during illness. It was originally proposed as better nutritional marker than albumin because of its shorter half life, giving more of a “right now” nutritional assessment. Nowadays, neither test is considered useful for nutritional assessment. Instead one should use a clinical instrument based on a nutrition focused H&P.
From the Journal of Hospital Medicine’s Things We Do for No Reason series.
What’s the value in diagnosing malnutrition in the first place? Well, it identifies you and your hospital as having a population of patients with a markedly higher mortality. That’s good for reimbursement and severity adjustment, as the linked article points out. Does it help patients? The evidence that it leads to interventions that improve outcome is scant to none as far as I know. What I am prompted to do, at least, is give thiamine.