Defining the optimal cut-off values for liver enzymes in diagnosing blunt liver injury

Based on the results from a previous study from our institution published in a Japanese
journal 16], all blunt trauma patients admitted to Teikyo University Hospital Trauma and Critical
Care Center who underwent initial evaluation with abdominal contrast enhanced (CE)
multi detector-row computed tomography (MDCT) within 3 h after injury, were retrospectively
enrolled between May 2006 and July 2013. This study was approved by Teikyo University
Hospital Ethics Committee.

Admission data collected included the following: age, gender, mechanism of injury,
Glasgow Coma Scale (GCS), and Revised Trauma Score (RTS). All patients included in
the study were followed throughout their hospital stay. Injury Severity Score (ISS),
Probability of survival (Ps), interventions (laparotomy and/or angioembolization (AE)),
liver related complications, and mortality were recorded.

The admission values of AST and ALT were measured using LABOSPECT 008 Automatic Analyzer
or Clinical Analyzer Model 7600 (both Hitachi High- Technologies Corporation (Corp.),
Tokyo, Japan).

Hemodynamically normal patients, on admission or after initial resuscitation, underwent
CE-MDCT if at least one of the following criteria was fulfilled: (1) complaint of
severe abdominal pain, (2) peritonism, (3) external signs of abdominal injuries, (4)
presence of hematuria, melena or hematemesis, (5) abnormal radiographic findings commonly
associated with abdominal injuries (intraperitoneal free air, lower rib fracture,
pelvic fracture, or lumbar fracture) (6) positive abdominal focused assessment with
sonography in trauma (FAST), (7) acute anemia with hemoglobin 10 g/dl, (8) impaired
consciousness due to suspected traumatic brain injury.

CT was performed using a 64-slice MDCT scanner (Aquilion 64, TSX-101A/HA, Toshiba
Medical Systems Corp., Japan) with intravenous contrast material (Omnipaque 300 injection
syringe, Daiichi Sankyo Company (Co.), Limited (Ltd.), Tokyo, Japan or Oypalomin 300
injection syringe, Fuji Pharma Co., Ltd., Toyama, Japan) unless the patient was known
to suffer from chronic kidney disease.

The liver injury was defined from CE-MDCT scans based on Organ Injury Scale (OIS,
1994 revision) described by the American Association for the Surgery of Trauma 17]. Attending staff reviewed the CE-MDCT at the following morning conference, and consensus
was reached.

Statistical analysis was performed using the IBM SPSS Statistics version 22 for MacOSX
[International Business Machines Corp., New York, United States of America (USA)]
and the Microsoft Excel for Mac 2011 (Microsoft Corp., Washington, USA). Categorical
variables were presented as medians and underwent Chi square test. Continuous variables
were presented as median with interquartile range (IQR), and subjected to the Mann–Whitney
U test. All p values reported are two-sided, and p values 0.05 were considered to
indicate statistical significance.

Receiver operating characteristic (ROC) curve analysis was performed to define the
optimal cut-off values for AST and ALT 18]. Two additional analysis methods were used to determine the optimal cut-off values
objectively. The first method was ‘The closest to (0, 1) criteria’, in this paper
called ‘upper-left (UL) index’, and represents the values at the shortest distance
from the upper left corner to the ROC curve. The second was ‘the Youden index’, which
describes the maximum vertical distance between the ROC curve and the diagonal or
chance line 19]. After determining the optimal cut-off values for AST and ALT with these methods,
sensitivity and specificity were calculated.