Creatinine Excretion as a Determinant of Accelerated Skeletal Muscle Loss with Critical Illness

The 24-h urinary creatinine excretion rate has been used as an approximation of the skeletal muscle (SM) mass in non-intensive care unit (ICU) settings. The study goal or aim was to determine reductions in SM mass in patients with recurrent critical illness who are admitted to a medical ICU.

Retrospective ICU patient records between 2013 and 2015 were reviewed. Inclusion of ICU patients with repeat 24-h urinary creatinine excretion levels at two different ICU admissions done routinely as part of care. The study design is a case series with patients as their own control.

Three patients were found to have data on two separate ICU admissions. The reduction in creatinine excretion among ICU patients was correlated with estimated SM mass. All patients had >50% reduction in creatinine excretion and ≥47% reduction in estimated SM mass over 4 months. All patients were bed-bound after the first ICU admission and met the definition of sarcopenia by the second ICU admission; all patients died during the second ICU admission. The final SM mass in all patients was <4 kg m^-2.

Patients with chronic critical illness admitted to the medical ICU, who become bed bound, can experience up to 50% reduction in SM mass as gleaned from creatinine excretion within 4 months. Low SM mass may predispose patients to increased mortality. Measurement of 24-h urinary creatinine excretion may be a useful ICU biomarker to determine SM mass for diagnostic and prognostic purposes.