Introduction: For patients bitten by a Green Pit Viper (GPV), the Ministry of Public Health (MoPH) guideline suggests a physician order blood tests immediately after the ED arrival and repeat them 2 h later, if initial results are normal. If repeat tests remain normal, the patient can be discharged and scheduled for outpatient-follow-up at 24, 48 and 72 h. Objectives: To determine the probability of abnormal blood tests at the second draw (2 h after the first draw), and to determine the probability of adverse events within 24+/−12 h among those discharged home for outpatient-follow-up. Methods: This retrospective study included patients with a history of GPV (Trimeresurus albolabris or Trimeresurus macrops) bite who were 15 years or older presenting to our ED from 2008 to 2015. We excluded those with other types of animal bites or those with missing medical records. Results: 320 cases were included. The majority were male (56.3%) and median age was 44 years old. There were only 4 cases (1.3%) with abnormal venous clotting time (VCT) or platelet count (PC) at the second blood draws when the first test results were normal. Of those discharged after the second blood draws came back normal, and who had outpatient follow-up at 24+/−12 h, 3 had minor adverse events and none received antivenom. Conclusions: This study showed a very low probability of abnormal test results 2 h after initial tests. However, they were still needed if the first tests were done too early. This study also confirms the safety of the guideline’s recommendation for outpatient follow-up, especially within the first 24 h, with a very low rate of minor adverse events, and instruction to seek immediate medical attention if symptoms worsen.