A 75-year-old man presents to the emergency department with fatigue. He has had severe nausea, vomiting, and diarrhea for the past 3 days. Today, his wife noticed that he was confused. The patient has a history of coronary artery disease with a drug-eluting stent placed 1 year ago, obesity, hypertension, and dyslipidemia. He denies chest pain or dyspnea, but complains of diffuse abdominal pain. His temperature is 99.0°F (37.2°C), blood pressure is 100/60 mmHg, pulse is 105/min, and respirations are 22/min. Physical exam reveals a confused man with dry mucous membranes. His abdomen is diffusely tender to palpation. Laboratory studies are ordered and notable for the following:

Serum:
Na+: 147 mEq/L
Cl-: 112 mEq/L
K+: 3.5 mEq/L
HCO3-: 14 mEq/L
BUN: 80 mg/dL
Glucose: 100 mg/dL
Creatinine: 2.1 mg/dL
Troponin: 0.10 mcg/L (normal < 0.01 mcg/L)

An ECG is ordered and is pending. Which of the following is the most appropriate management of this patient's elevated troponin?
Aspirin, heparin, clopidogrel, and cardiac catheterization
Ringer lactate bolus
Metoprolol and aspirin
Obtain a urinalysis and creatine phosphokinase level
Ringer lactate bolus
This patient with likely gastroenteritis (given his nausea, vomiting, and diarrhea) is dehydrated, as indicated by his low blood pressure, tachycardia, dry mucous membranes, and prerenal kidney injury (elevated BUN and creatinine with BUN:creatinine ratio > 20:1) in the setting of an anion gap (anion gap = [Na+] - [Cl-] - [HCO3-] = 147 - 112 - 14 = 21). His elevated troponin is likely secondary to poor renal clearance and dehydration, which is most appropriately addressed with IV fluids such as Ringer lactate.

Troponin is a lab marker classically thought to be elevated when there is an injury to the heart causing leakage of this enzyme from the cardiac myocyte. However, there are many possible causes of an elevated troponin that may not be directly cardiac in nature or related to myocardial ischemia. Acute kidney injury is a common cause of an elevated troponin. For this reason, patients with an elevated troponin with kidney dysfunction without any cardiac symptoms or ECG changes should have their renal etiology addressed, and this will often clear the troponin. In the setting of a prerenal injury (dehydration causing poor kidney perfusion and a BUN:creatinine ratio > 20:1), IV fluids will restore perfusion and treat the underlying cause. Patients with chronic kidney disease or kidney failure should have an ECG obtained and their current troponin should be compared to previous troponin levels to ensure it is not higher than their baseline. If there is uncertainty regarding a troponin level, it can be trended to see if it is rising, falling, or staying the same. Correlation with clinical symptoms is important when evaluating an elevated troponin level.

Masri et al. review the causes of an elevated troponin. They note that a troponin elevation can be seen in myopericarditis, renal failure, heart failure, pulmonary embolism, septic shock, rhabdomyolysis, stroke, and many other possible causes that are not related to myocardial infarction. They recommend keeping a broad differential and correlating the troponin with the patient's clinical presentation.

Incorrect Answers:
Answer A: Aspirin would be appropriate management of an elevated troponin secondary to acute coronary syndrome as its antiplatelet activity reduces mortality. It should be administered prior to performing an ECG in patients with chest pain thought to be from a cardiac etiology.

Answer B: Aspirin, heparin, clopidogrel, and cardiac catheterization is appropriate management of a ST elevation myocardial infarction, which presents with chest pain, diaphoresis, dyspnea, and ST elevation within a vascular distribution with reciprocal changes on ECG. This patient has no cardiac symptoms and has a better alternative explanation for their troponin elevation.

Answer C: Metoprolol and aspirin may be indicated in acute coronary syndrome, and metoprolol would reduce this patient's heart rate. However, note that this patient's tachycardia is secondary to volume depletion; thus, beta-blockade for sinus tachycardia is inappropriate and may make the patient hemodynamically unstable.

Answer D: Obtaining a urinalysis and creatine phosphokinase level may be performed in rhabdomyolysis which presents in the setting of seizures, electrical shock, heatstroke, or with vigorous exertion. Patients will complain of muscle pain, oliguria, and dark urine. Management is centered on the administration of large volumes of fluid to protect the kidney and clear the toxic myoglobin. Note that rhabdomyolysis may elevate the troponin; however, there is nothing in this patient's history that suggests rhabdomyolysis.

Bullet Summary:
Prerenal injury causing an acute kidney injury may elevate the troponin due to decreased renal clearance and should be addressed with the administration of fluids.