Abstract Body (Do not enter title and authors here): Background
Interstage programs decrease morbidity and mortality and are potentially resource intensive. The accurate cost of these programs is unknown. Understanding cost and outcomes of care is necessary to provide high-value care for this population. Time-driven activity-based costing(TDABC) provides an accurate way to understanding costs that occur at the level of the patient.

Research Question
What is the outpatient cost of the interstage period to the health care system?

Methods
Single-center study of outpatient interstage care. Direct observation (over 9 months) and retrospective review were utilized to develop process maps. Outpatient interstage and pediatric visits were timed by 5 observers. Cost of personnel was calculated in dollars per minute utilizing median national health system salary data.

Results
Patients attended a median of 13 cardiology, 5 pediatric, 3 physical therapy(PT), 4 occupational therapy(OT), and 7 speech therapy(SLP) visits while interstage. Total cost of interstage visit personnel was $258.18[$208.59-$389.24] and equipment cost was $1457.79. Total cost of a pediatric visit was $123.55[$130.80-$167.12]. Total cost of outpatient PT, OT, and SLP was $70.58, $66.68 and $72.43, respectively. Total cost of the outpatient interstage period was $6417.38[$5808.94-$8338.96] per patient.(Table) In interstage clinic, patients spent 132[89-165] minutes with providers and 64[41-66] minutes waiting.(Figure) In pediatric clinic, patients spent 73[71-76] minutes with providers and 9[6-13] minutes waiting.

Conclusion
This work demonstrates that while challenging, TDABC analysis can be applied to complex interstage care to understand costs and move to deliver high-value care for this population. While caring for a child during the interstage period is time and resource intensive, it carries a relatively low cost to the health care system with a total cost of $6417.38 per patient. Additional work is needed to understand costs of inpatient interstage care.