Veja esta postagem no blog dos blogs do MSDN.
Citações do blog:
A BitLocker volume has a clear-text BPB much like FAT and NTFS. The BPB is located at the first 0x54 bytes of the first sector of the volume.
Além disso:
BitLocker stores multiple copies of the volume metadata, and the first copy can be located from information in the BPB. The byte offset of the first metadata location is calculated as MetadataLcn * SectorsPerCluster * BytesPerSector.
Há também a consulta WMI GetEncryptionMethod
disponível, conforme instruído na postagem do blog.