METHODS:
Riboflavin,
FMN and
FAD concentrations were measured, by HPLC, in plasma and red cells in healthy subjects (n=119) and in
critically ill patients (n=125) on admission and on follow-up.
RESULTS: On admission, compared with the controls,
critically ill patients had significantly higher plasma
riboflavin and
FMN concentrations (p<0.001) and lower median plasma
FAD concentrations (p<0.001). In the red cell,
FAD concentrations were significantly lower in
critically ill patients (p<0.001). In healthy subjects, plasma
riboflavin was directly associated with both plasma
FMN (r(s)=0.55, p<0.001) and plasma
FAD (r(s)=0.49, p<0.001). Red cell
riboflavin was directly associated with red cell
FMN (r(s)=0.52, p<0.001) but not red cell
FAD. In the
critically ill patients, plasma
riboflavin was not significantly associated with either plasma
FMN or
FAD. Red cell
riboflavin was directly associated with red cell
FMN (r(s)=0.79, p<0.001) and red cell
FAD (r(s)=0.72, p<0.001). Longitudinal measurements (n=60) were similar.
CONCLUSIONS: The relationship between plasma
riboflavin,
FMN and
FAD was significantly perturbed in
critical illness. This effect was less pronounced in red cells. Therefore, red cell
FAD concentrations are more likely to be a reliable measure of status in the
critically ill patient.