Liver Enzymes as Predictors of Liver Damage due to Blunt Abdominal Trauma in Children.

ABSTRACT

Background. Blunt abdominal trauma in children can result in injury to the liver. In hemodynamically stable patients, initial evaluation of liver transaminase levels may be useful in determining the need for computed tomography (CT).

Methods. We reviewed the medical records of 44 hemodynamically stable children who had abdominal CT and who also had liver enzyme determinations as the initial workup.

Results. Liver enzymes were found to be elevated in all but one patient with CT confirmed hepatic injury. The sensitivity and specificity of elevated liver enzyme levels were 92.9% and 100%, respectively, for predicting liver injury.

Conclusions. When hemodynamically stable pediatric patients with blunt abdominal trauma have AST levels >400 and/or ALT levels >250 IU/L, abdominal CT is indicated. Children in this study with serum transaminase levels below these values were at decreased risk of liver injury.

TRAUMATIC INJURIES are the leading cause of death in children more than 1 year of age. (1,2) Blunt trauma is a common cause of multiple injuries in children, and many of them will have internal injuries without external physical findings to suggest internal injury. Blunt trauma is a nonpenetrating injury without open wounds with little to no external blood loss even though there is a high probability of bleeding in abdominal injuries. Mechanisms of these injuries include, but are not limited to, motor vehicle crashes (with victim as passenger, pedestrian, or bicyclist), fall, and intentional injuries. The organs most frequently injured are spleen, liver, and kidney. Serious intra-abdominal injuries occur in about 8% of children admitted to pediatric trauma centers, and hepatic injury is present in 27% of these cases. (3) In hemodynamically unstable children, there is little opportunity for computed tomography (CT) scans while waiting for the results of the liver enzyme studies, but in children who are stable there is adequate time for studies to either establish or exclude the presence of liver injury. Although CT is a valuable imaging technique in evaluating solid organ injuries, it is expensive and can be time consuming. All pediatric patients brought to the emergency department after trauma have blood drawn for a trauma panel. This includes complete blood cell count (CBC), aspartate aminotransferase (AST), alanine amino transferase (ALT), type, and screen. Elevation of hepatic enzymes has demonstrated correlation with CT-confirmed liver injury. Both AST and ALT enzymes are predominantly formed in the mammalian liver and have a significant role in the degradation of amino acids. On blunt abdominal trauma, the resulting cellular disruption breaks open the hepatic cell, causing an outpouring of the cytoplasmic contents. This releases AST and ALT enzymes that were previously enclosed in the cell membrane into the bloodstream. Thus, biochemical tests of serum levels of AST and ALT are useful in evaluating the cell for damage and may indicate whether CT is warranted. The present study was undertaken to determine the accuracy of liver enzyme measurement in predicting liver injury associated with pediatric blunt abdominal trauma.

MATERIALS AND METHODS

Medical records of all pediatric patients with suspected blunt abdominal trauma seen by the Broward General Medical Center Trauma Service between January 1992 and April 1998 were reviewed. According to Florida guidelines, patients from birth to 15 years of age were included. Data collected on all patients included age, sex, mechanism of injury, physical findings, results of CBC, serum AST level, serum ALT level, radiographic evaluation including CT scans, outcome of injury, operative reports, ICD-9 codes describing anatomic nature of injury, and hospital course. Hepatic injury was diagnosed if the radio1 aginst reported the presence of liver injury n review of the CT scan. Asyrnptomatic children whose CT scan did not show a hepatic injury were included as a comparison group. Serum transaminase levels at time of admission were used for analysis. Differences between mean AST and ALT levels were analyzed by the t test comparing those patients whose CT scan showed hepatic injury versus those without injury. An a ttempt to determine which levels would be most predictive of injury was evaluated by sensitivity, specificity, and positive and negative predictive values.

RESULTS

All 44 patients brought to the emergency department and classified on arrival as having blunt abdominal trauma had abdominal CT scan with intravenous contrast medium and were admitted to the hospital. No patient died, and none required surgical intervention or treatment of injuries related to an abdominal organ. Table 1 summarizes the general characteristics of the study sample. According to t test, patient age, sex, and mechanism of injury were not significantly different between the groups with and without liver injury.

The mean AST and ALT levels for patients with hepatic injury were 1,128 IU/L [+ or -]850 (SD) and 685 IU/L [+ or -] 350 (SD), respectively. In those without hepatic injury visible on CT scan, these values were 139 IU/L [+ or -] 112 (SD) and 80 IU/L [+ or -] 71 (SD), respectively. The difference is shown in the Figure.

In this study, serum AST levels >400 IU/L and/or serum ALT levels >250 IU/L yielded the highest sensitivity and specificity. Of the 14 patients who had marked elevation of serum transaminase levels, all 14 had liver injury visible on CT scan (Table 2). Thirty-one patients had AST and ALT levels <400 IU/L and <250 IU/L, respectively. One of these patients had liver injury visible on CT scan. The sensitivity, specificity, and positive and negative predictive values of AST levels >400 IU/L and/or ALT levels of >250 IUI/L in identifying hepatic injurywere 92.9%, 100%, 100%, and 96.8%, respectively (Table 2). Table 3 summarizes the type and extent of injuries visible on abdominal CT.

DISCUSSION

Blunt abdominal trauma is a common injury in childhood, with a mortality rate estimated to be 10%. (4) In hemodynamically unstable patients, quick surgical intervention is often needed. In hemodynamically stable patients, an undetected hepatic injury can result in serious morbidity and even mortality. Since most hepatic injuries in these stable patients can be treated nonsurgically, these patients need to be identified so that appropriate nonsurgical observation plans can be instituted. This primarily involves close observation in the pediatric intensive care unit, follow-up of vital signs, serial measurement of hemoglobin and hematocrit levels, and in some patients, blood transfusion. A concern is that some may continue to show evidence of bleeding, necessitating surgical intervention. Abdominal CT has proven itself as a valuable diagnostic tool for evaluating intra-abdominal injury, but it is an expensive test and can be time consuming. In a hemodynamically stable child with a possible injury, serum liver transaminase levels can be of assistance in determining whether CT of the abdomen should be done. The biochemical test can provide a relatively inexpensive and quick alternative to routine CT scanning of every patient.

Measuring the concentration of serum transaminase was reported in a study by Haftel et al (5) in which serum transaminase levels (AST and ALT >35 IU/L) had no significant correlation with positive CT scans. Lack of correlation in their study may be the result of low AST and ALT levels used to delineate those at risk of hepatic injury. A contusion or laceration must be great enough to cause elevation above certain levels. On the other hand, in a prospective study to investigate the possible relationship between hepatic injury and elevated serum transaminase levels, Oldham et al (6) used a higher range of values that were considered significantly elevated. They found that if abnormally elevated serum transaminase levels (AST >200 and ALT >100 IU/L) were used as a screening test before obtaining abdominal CT scan, the yield for the CT scan with positive results would rise from 43% to 62%. This increase in cutoff level produced a greater degree of accuracy in defining those at risk of hepatic injury. Hennes et a l (4) concluded from their study of 63 patients that cutoff levels at higher serum transaminase values (AST >450 and ALT >250 IU/L) accurately identified children with hepatic injury in 89.5% of cases.

We found that the measurement cutoff of AST at >400 and ALT >250 IU/L classified those who were most likely to have hepatic injury. Comparison of the serum transaminase levels between injured and noninjured patients revealed significant differences. Thus, AST and ALT tests appear to be sensitive indicators of hepatocellular injury.

Despite the high levels of sensitivity and specificity of positive determination of patients with hepatic injury, there was one patient with hepatic injury found on CT scan with AST and ALT levels greatly below the cutoff level for suspected liver injury. This patient had AST and ALT levels of 145 and 149 IU/L, respectively. If serum transaminase levels were the sole criterion for evaluating the presence of hepatic injury in blunt abdominal trauma, this patient would have been misdiagnosed. Theoretically, it is possible that a patient with hepatic disorder may not have significant elevation of liver enzymes. However, in this particular patient, there was no evidence of any hepatic disorder. Therefore, use of serum transaminase levels should not be the sole criteria in deciding need for abdominal CT scan. Clinical evaluation also plays a significant part in that decision.

Two other aspects of this biochemical study deserve mention. The degree of liver enzyme elevation above the threshold levels does not seem to correlate accurately with severity of injury or need for surgical intervention. Second, the levels of serum enzyme elevation by themselves are not useful as predictors of outcome. However, Nishida et al (7) found that preoperative ALT level combined with base excess and platelet count may assist as a prognostic factor for hemorrhagic death after liver trauma. They believe the preoperative ALT value is indicative of the amount of the damage to liver tissue. This aspect needs further study.

In hemodynamically stable children with blunt abdominal trauma, significant elevation of liver enzymes (AST >400 and ALT >250 IU/L) will identify the majority of children at risk of having hepatic injury. Computed tomography should be obtained on these children to detect possible liver injury. Patients who do not show significant elevation of transaminase levels after blunt abdominal trauma are at decreased risk of injury but should be carefully monitored by repeated physical examination. The clinical picture should be considered also in deciding the need for CT scan of the abdomen. Elevated liver enzyme levels should not be the sole criterion in making that decision.

From the Division of Trauma Services, Broward General Medical center, Fort Lauderdale, Fla.

Reprint requests to Subbash R. Puranik, MD, 300 NW 70th Aye, Suite 202, Fort Lauderdale, FL 33317.

References

(1.) Mayer T, walker M, Berger P: causes of morbidity and mortality in severe pediatric trauma. JAMA 1981; 245:719-721

(2.) Roche BC, Bugmann P, LeCoultre C: Blunt injuries to liver, spleen, kidney and pancreas in pediatric patients. Eur J Pediatr Surg 1992; 2:154-156

(3.) Cooper A: Liver injuries in children: teatments tried, lessons learned. Semin Ped Surg 1992; 1:152-161

(4.) Hennes MS, Smith DS, Schneider K, et al: A predictor of liver injury. Pediatrics 1990; 86:87-89

(5.) Haftel A, Lev R, Manhour C, et al: Abdominal CT scanning in pediatric blunt trauma. Ann Emerg Med 1988; 17:684-689

(6.) Oldham KT, Guice KS, Kaufman PA: Blunt hepatic injury and elevated hepatic enzymes: a clinical correlation in children. J Pediatr Surg 1984; 19:457-461

(7.) Nishida T, Fujita N, Nakao K, et al: A multivariate analysis of the prognostic factors in severe liver trauma. Surg Today 1996; 26:389-394

[Graph omitted]

TABLE 1

Demographic Characteristics of the Sample (*)

                     No.(%) With   No.(%) without
Characteristic       Liver Injury   Liver Injury

Sex
  Male                 4 (28.6)       9 (30)
  Female              10 (71.4)      21 (70)

Age (years)            6.19           6.16

Mechanism of injury
 MVA (pedestrian)      4 (28.6)       9 (30.0)
 MVA (passenger)       3 (21.4)      10 (33.3)
 MVA (bicycle)         1 (7.1)        2 (6.7)
 Fall                  1 (7.1)        3 (10.0)
 Other                 5 (35.8)       6 (20.0)

(*)None of the differences were statistically significant.

MVA = Motor vehicle accident.
TABLE 2

Association Between Transaminase Level and Results of Computed
Tomography (*)

                        Hepatic   No Hepatic
  Transaminase Level     Injury     Injury
        (IU/L)          (n = 14)   (n = 30)   Sensitivity  Specificity

AST>450 and/or ALT>250     13         0          92.9%        100%
AST<450 and/or ALT<250     1          30

                         Positive    Negative
  Transaminase Level    Predictive  Predictive
        (IU/L)            Value       Value

AST>450 and/or ALT>250     100%       96.8%
AST<450 and/or ALT<250

AST = Aspartate aminotransferase

ALT = alanine aminotransferase.
TABLE 3

Findings on Abdominal Computed Tomography

                       No.(%)        No. (%)
                     With Injury  Without Injury
Findings              (n = 14)       (n = 30)

Spleen injury         1 (7.1%)      15 (50.0%)
Kidney injury         0              9 (30.0%)
Pulmonary contusion   5 (35.7%)      5 (16.7%)
Hepatic injury (*)
 Laceration           9 (64.3%)      0
 Contusion            5 (35.7%)      0
 Hematoma             4 (28.6%)      0

(*)Four patients had more than one type of injury.

RELATED ARTICLE: KEY POINTS

* This study collected data by retrospective medical record review.

* Included in the study were the medical records of 44 hemodynamically stable children who had abdominal computed tomography to evaluate blunt abdominal trauma

* Liver enzyme levels were analyzed by hepatic injury. Risk of injury was related to aspartate aminotransferase and alanine aminotransferase levels.