Systematic comparison of routine laboratory measurements with in-hospital mortality: ICU-Labome, a large cohort study of critically ill patients.

BACKGROUND: In intensive care unit (ICU) patients, many laboratory measurements can be deranged when compared with the standard reference interval (RI). The assumption that larger derangements are associated with worse outcome may not always be correct. The ICU-Labome study systematically evaluated the univariate association of routine laboratory measurements with outcome.

METHODS: We studied the 35 most frequent blood-based measurements in adults admitted ≥6 h to our ICU between 1992 and 2013. Measurements were from the first 14 ICU days and before ICU admission. Various metrics, including variability, were related with hospital survival. ICU- based RIs were derived from measurements obtained at ICU discharge in patients who were not readmitted to the ICU and survived for >1 year.

RESULTS: In 49,464 patients (cardiothoracic surgery 43%), we assessed >20·106 measurements. ICU readmissions, in-hospital and 1-year mortality were 13%, 14% and 19%, respectively. On ICU admission, lactate had the strongest relation with hospital mortality. Variability was independently related with hospital mortality in 30 of 35 measurements, and 16 of 35 measurements displayed a U-shaped outcome-relation. Medians of 14 of 35 ICU-based ranges were outside the standard RI. Remarkably, γ-glutamyltransferase (GGT) had a paradoxical relation with hospital mortality in the second ICU week because more abnormal GGT-levels were observed in hospital survivors.

CONCLUSIONS: ICU-based RIs for may be more useful than standard RIs in identifying ICU patients at risk. The association of variability with outcome for most of the measurements suggests this is a consequence and not a cause of a worse ICU outcome. Late elevation of GGT may confer protection to ICU patients.