The Utility of Laboratory Testing in Pediatric Trauma: A Primer

Causes of traumatic pediatric death by mechanism, with a clear majority found in MVCs. (1)

Approximately 6,200 infants and adolescents die annually in the United States due to unintentional injuries, with the majority of injuries attributed to motor vehicle trauma. In addition to these deaths, over 9 million children visit  pediatric emergency departments annually for unintentional injuries (1). As emergency medicine physicians, we have the primary responsibility of diagnosing and managing these patients rapidly in order to allow for the most favorable outcomes. The most important method in determining the severity of presenting trauma in a pediatric patient is a thorough primary and secondary survey. However, in the process of rapidly managing a pediatric patient’s injuries, laboratory studies can serve as useful adjuncts. This post serves to highlight the key laboratory studies that should (and should not) be considered in the setting of two common sources of major pediatric trauma: blunt thoracic trauma and blunt abdominal trauma.

Case 1

It’s a Friday night at the pediatric emergency department when all of a sudden your trauma pager goes off. You immediately rush to the trauma bay and there lies a 13 year-old male that presents after an MVC. Airbags were deployed with no loss of consciousness. The patient was able to ambulate on scene. Initial vitals are: HR: 120; BP: 100/60; SpO2: 96%; RR: 22. The patient is GCS 15. He is able to talk to you and says his chest hurts. Primary survey intact. Secondary survey reveals bruising over the anterior right chest.

+ Should I order an EKG in this patient?

The most recent multicenter retrospective study evaluating the efficacy of EKG for blunt cardiac injury reviewed 184 patients across 16 centers that were diagnosed with myocardial contusion, myocardial concussion, or myocardial laceration (2). For the 184 patients analyzed, 73 patients (39.7%) presented as pedestrian vs. auto, 71 patients (38.6%) presented in a motor vehicle collision, and 13 patients (7.1%) presented as auto vs. bicycle. The remainder of the patients had other presenting injuries including crush injuries, horsekicks, falls, assaults, sledding injury, soccer injury, and biking into a parked car. 52% of patients presented with hemodynamic instability (hypotension and tachycardia) and 60% of patients presented with external evidence of thoracic trauma. In the study, 82% (150 patients) were selected to receive an EKG via the specific institution’s protocol for pediatric blunt thoracic trauma. Of the 150 patients, 57% (86 patients) presented with abnormalities in their EKG including ST-T wave changes, new bundle branch blocks, sinus tachycardia, supraventricular arrhythmia, and ventricular arrhythmia (2). Given that the majority of patients with documented cardiac injury had an abnormal EKG on initial presentation, clinicians should consider the use of EKG in the setting of pediatric blunt thoracic trauma.

Abnormalities in EKG, such as electrical alternans, can often prompt further diagnostic testing to further delineate the cause of a patient’s condition. Bedside ultrasound is often used following an abnormal EKG as a rapid way to determine if the patient has a pericardial effusion/tamponade secondary to myocardial rupture and for wall motion abnormalities suggestive of blunt cardiac injury (3). If bedside ultrasound reveals any abnormalities, it is important to obtain a comprehensive echocardiogram for thorough investigation of a patient’s cardiac function.

An EKG was ordered with the following results:

Sinus tachycardia with rate related ST changes (4)

+ Is there any value in ordering a troponin for this patient?

Currently, there is unclear evidence on value of troponin levels in the evaluation of pediatric trauma. In a review of cardiac troponin I in the setting of cardiac injury, 7 pediatric patients that were hospitalized for blunt thoracic trauma had troponin levels measured at initial presentation. In 4 of these patients that were determined to have a high likelihood for blunt cardiac injury/myocardial contusion based on abnormalities in EKG or echocardiogram, 3 patient displayed troponin I levels greater than 2ng/mL. The other 3 patients with a low likelihood for BCI as determined by normal EKG’s and echocardiograms had troponin levels lower than 2 ng/mL. Despite this correlation in the elevation of troponin I levels for those with suspected BCI, larger multicenter trials are required to fully determine if initial troponin I levels have utility in the screening of blunt cardiac injury in setting of pediatrics (5).

Large sample size cohort studies and retrospective studies have been performed in adults with contrasted findings. In a prospective study analyzing the use of troponin in 187 patients presenting for blunt thoracic trauma, it was determined that an evaluation of troponin of greater than 1.05 micrograms/L correlated with an increased likelihood for myocardial injury (6). In contrast, a retrospective study analyzing the use of initial troponin measurements in 359 patients with blunt thoracic trauma determined no evidence of increased troponin in patient diagnosed with myocardial contusion (as determined by abnormalities in EKG and echocardiography) (7). Therefore, given the contrasting evidence in the use of cardiac biomarkers, current guidelines recommend considering initial troponin levels only in hemodynamically unstable patients presenting for blunt thoracic trauma.

You elect not to order a troponin on your patient and proceed to evaluate your patient via a CXR. CXR demonstrated a 5th and 6th right posterior rib fractures and the patient was admitted for observation with serial pulmonary exams to monitor the development of pulmonary contusion. Pain control was provided resulting a resolution of your patient’s tachycardia.

Case 2

Shortly after dispositioning your 13 year-old male patient, you go back to the break room to grab some much deserved coffee. While pouring that sweet black nectar into your cup, your trauma pager goes off again. You rush to the trauma bay and there lies an 8 year-old female that is presenting after an MVC. Initial vitals are as follows: HR: 145; BP: 90/57; SpO2: 98%; RR: 18. She is crying profusely and yelling that her tummy hurts. Primary survey is intact. Secondary survey reveals a seat belt sign over lower abdomen.

+ Should I order a CBC in the setting of blunt abdominal trauma?

Although initial hemoglobin and hematocrit can be normal due to lack of equilibration of intravascular volume, an initial CBC demonstrating low hematocrit may be indicative of massive hemorrhage within the abdomen (8). Given that a FAST examination does not evaluate the retroperitoneum, a low hemoglobin can be an adjunct in determining the location of suspected hemorrhage if FAST examination is negative (9). An initial normal CBC in a hemodynamically stable patient with abdominal pain can be trended to determine if intra-abdominal hemorrhage is present or is developing (9). For all patients, a type and screen should also be ordered in the event that patient will need resuscitation with blood product (if crystalloids are not improving status) or if the patient requires a surgical intervention.

While waiting for your CBC results, a FAST Examination was performed which was negative.

Comparison of LFT sensitivity, specificity and negative predictive value in the setting of pediatric trauma to rule out or in intra-abdominal injury

+ Given the low sensitivity of FAST in pediatric trauma, is it worth obtaining LFTs for this patient?

Liver function tests have proven to be useful adjuncts in suggesting intra-abdominal injury (IAI) in the setting of blunt abdominal trauma. Intra-abdominal injury can be defined as abdominal organ or tissue damage resulting in bleeding, contamination, or end-organ dysfunction. In a prospective study from Holmes et al. that analyzed 1095 pediatric patients under the age of 16 presenting with blunt abdominal trauma, it was determined that with an AST >200 and an ALT >125 demonstrated a specificity of 96% for IAI when compared to a gold standard of computed tomography with IV contrast of the abdomen/pelvis. Sensitivity was recorded at 50%; therefore, LFTs should only be used to rule in the possibility of IAI based off the data in this study (8,9). Increased sensitivities have been noted in studies where the cut-off for AST/ALT are increased. For example, in a study from Hennes et al. demonstrated a sensitivity and specificity of 100% and 92.3% respectively when using cutoffs of AST>450 and ALT>250 (10). However, a more recent study by Zagary et al. that analyzed 247 pediatric patients that experienced blunt abdominal trauma used an AST/ALT cutoff of 400/200 with a sensitivity and specificity of 59% and 86% respectively (11). Therefore, in the setting of pediatric abdominal trauma, a clinician should consider the use of LFTs as an adjunct to further suggest if a patient has suffered intra-abdominal injury.

+ Should I order an amylase or lipase as well to evaluate for pancreatic injury?

In setting of suspected acute pancreatitis, amylase/lipase have served as useful adjuncts to determine if a person is suffering from pancreatic injury. However, in the realm of blunt abdominal trauma, multiple studies have demonstrated little correlation between amylase/lipase and acute pancreatic injury and have also shown that amylase/lipase can be non-specifically elevated (12,13). The largest retrospective study to determine the efficacy of amylase/lipase was conducted by Adamson et. al which analyzed 1,821 pediatric trauma patients over 64 months. From these 1,821 patients, 507 patients had amylase/lipase testing with 116 (23%) demonstrating elevated amylase/lipase levels. 74 of the patients with elevated amylase/lipase underwent CT of the abdomen and pelvis with 38 (51%) of the patients having normal scans. Only 5 (1%) patients out of the 507 tested for amylase/lipase had elevated levels with true pancreatic injury (14). In a prospective study conducted by Bucheter et. al for 83 pediatric patients that undergone blunt abdominal trauma, 45 patients (53%) had an elevation of either amylase/lipase over a 7 day period, however, only 1 (1%) patient demonstrated pancreatic injury (12). Therefore, although an elevated lipase/amylase can suggest the possibility of IAI, they should not be ordered to evaluate for pancreatic injury in the setting of pediatric blunt abdominal trauma.

 You elect not to order an amylase/lipase for this patient. Your CBC comes back with an H/H of 11.1/33.8. LFTs are elevated with an AST of 240 and ALT of 130. On secondary survey, you note there is no blood at the urethral meatus. Given the mechanism of the patient’s injury, you contemplate the possibility of genitourinary trauma.

+ What is the utility in obtaining a urinalysis in the setting of blunt abdominal trauma?

Genitourinary injuries are common in the setting of blunt abdominal trauma (15). In the absence of blood at the urethral meatus during primary survey, hematuria present in UA can rule in the possibility of genitourinary trauma with location of injury determined by CT of the abdomen and pelvis. To minimize the amount of radiation endured by the pediatric population, current guidelines recommend a CT when UA demonstrates 50 RBCs/hpf (16,17). In the event that a hemodymically stable patient does not exhibit >50 RBCs/hpf on UA but physical signs of renal injury such as significant CVA tenderness, a CT may be indicated to rule out genitourinary injury.

UA results are unremarkable. A chest X-Ray and pelvis X-ray were performed with no acute cardiopulmonary abnormalities or bony abnormalities. Given the elevated LFTs measured previously, you elect to obtain a CT of the abdomen and pelvis with IV contrast. CT Scan demonstrates a Grade II liver injury with a 5 cm laceration overlying Zone 5 and 6 with 1cm of parenchymal depth. You elect to admit the patient to the PICU for further management of his injuries and mild anemia.

Post by Shan Modi, MD

Peer Review and Editing by Ryan LaFollette, MD


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