According to the CCRN website, ED nurses can take the CCRN exam. So your ED experience would count toward experience needed to sit for the exam. However, whether it would be helpful is another question. What is your motivation for taking the exam? Is it to enhance your resume? Make yourself more marketable? Eventually take an ICU position? The exam costs 220 for AACN members and 325 for non-members, so it's a lot of money if you don't really need the credentials. There are also emergency nurse cerficiations and trauma nurse certifications.
Here is the link to FAQ about CCRN:
Some parts you might be most interested in:
Who is eligible to sit for the CCRN certification exam?
The CCRN exam is for nurses who work at the bedside of acutely or critically ill patients, regardless of the setting (includes areas such as ICU, CCU, Emergency Department, Trauma Unit, Interventional Radiology/Cardiology, and Critical Care Transport/Flight). Certain other units with high acuity patients may also be eligible; please contact AACN Certification Corporation to inquire.
What areas does the CCRN exam cover?
The CCRN exam is weighted most heavily in the areas of Cardiovascular, Pulmonary, Multi-system and Professional Caring and Ethical Practice. Pulmonary questions address ventilator settings and how they would be adjusted according to ABG results. Cardiovascular items include hemodynamic settings, as well as questions about MI, CHF, PE, and IABP. If you are not familiar with or do not have experience in caring for these types of patients, we recommend that you gain the necessary experience before taking the exam.
^^ Notice that in the above question it says that the CCRN covers vent settings and adjusting them based on ABG results. You probably don't do a lot with vents and repeat AGBs in the ED. So you might want to learn more about them before taking the CCRN.