I'd let them use the sample they already have. I'd also encourage you to try getting a test done through IGeneX - http://www.igenex.com/ because LabCorp does not report all the Lyme-Specific bands on the Western Blot (they omit bands 31 and 34, which are outer surface proteins and very specific for Bb/Lyme).
IGeneX will send you a kit for the bloodwork required. Just make sure you list a doctor to whom they can report results on the necessary form. At the bare minimum, I'd recommend tests #188 and #189 (Lyme Western Blot IgG and IgM).
Chronic Lyme Disease, Chronic Bartonella (clinical dx only), Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication/Chemical Allergies & Intolerances, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD ("Secondary Lupus-Like Syndrome"), Osteoporosis, chronic Lymphopenia, etc.; G-Tube; Currently weaning off TPN.
Meds: Pulmicort, IV Doxycycline, Heparin (to flush PICC line), Claritin, Singulair, Domperidone, Colloidal Silver (topically & nasally), probiotics, Liver support herbs, Ailanthus, digestive enzymes, homeopathy.