For patients with xanthelasma, aside from a lipid panel, do you perform any additional lab workup or send referrals?   

It is reasonable to get a lipid panel and screening thyroid dysfunction labs (tsh, t4, and t3). Since xanthelasma are benign but often recur, I think an important aspect here is managing expectations. Let the patient know that recurrence is common and not associated with poor surgical techniques.