O2097: Utility of Routine Postoperative Laboratory Testing After Posterior Spinal Fusion for Adolescent Idiopathic Scoliosis

Background: Adolescent idiopathic scoliosis (AIS) is a common spine condition in children. Surgical treatment is generally considered safe with few complications. Perioperative blood loss is a major risk, which may necessitate the transfusion of allogeneic red blood cells, carrying risks of infection and alloimmunization, as well as hemolytic, febrile, and allergic reactions. With modern improvements of blood management strategies such as the use of intraoperative cell salvage and the use of tranexamic acid, the risk of perioperative transfusion has significantly diminished. Despite low rates of symptomatic acute anemia, routine laboratory blood draws on post-operative day 1 (POD1) and beyond are still commonplace. We hypothesized that perioperative transfusion events can be predicted based on several risk factors, and that the majority of patients who undergo surgical treatment of AIS may otherwise be exempt from routine postoperative laboratory testing.

Methods: We performed a retrospective cohort study of consecutive patients age 11-19 with AIS who underwent posterior spinal fusion at a single institution. Patient characteristics and operative details were recorded (Table 1). The proportion of patients who had a hematocrit level ≤22% on POD1 and those who required postoperative transfusion were estimated with a 95% confidence interval. Univariable logistic regression was utilized to determine if there were factors associated with patients having a hematocrit ≤22% on POD1 or a postoperative transfusion. Firth’s penalized logistic regression was used for any separation in the data. Youden’s index was utilized to determine the optimal point on the ROC curve that maximizes both sensitivity and specificity. P-values less than 0.05 were considered significant.

Results: Of the 527 patients, only eight (2%) had POD1 hematocrit ≤22%, none of whom underwent transfusion. These patients had lower last intraoperative hematocrit levels compared to patients with POD1 hematocrit >22% (24.1% vs 31.5%, p< 0.001), and there was no difference in preoperative hematocrit levels in this group (38.2% vs 39.8%, p=0.11). Four patients underwent postoperative transfusion. Both preoperative hematocrit levels (34.0% vs 39.9%, p=0.001) and last intraoperative hematocrit levels (25.1% vs 31.4%, p=0.002) were lower compared to patients who did not undergo transfusion (Table 1). Intraoperative hematocrit < 26.2%, operative time of more than 35.8 minutes per level fused, or cell salvage of more than 241cc were significant risk factors for postoperative transfusion (relative risk of 105.6; 28.6; and 9.8, respectively) (Table 2). No other risk factors were associated with postoperative transfusion.

Conclusion: Postoperative transfusion after posterior spinal fusion for pediatric AIS is exceedingly rare, and routine blood laboratory testing is unnecessary. POD1 labs should be considered when last intraoperative hematocrit < 26%, operative time per level fused >35 minutes, or cell saver amount is >241cc. Otherwise, unless symptomatic, patients do not benefit from additional laboratory screening on POD1 and beyond.