Reed is one of five changes made by Director of Rugby Mark Hammett as Blues target a third win of the season in the league.
Argentina international duo Lucas Amorosino and Joaquin Tuculet, who scored a spectacular try on his debut for the region against Benetton Treviso last month, both earn recalls after missing European action.
Scrum half Lewis Jones will partner Gareth Anscombe at half back, with Lloyd Williams missing the game through injury.
Hooker Kristian Dacey is also named in the front row alongside captain Gethin Jenkins and Adam Jones.
Scrum half Tavis Knoyle and centre Tom Isaacs both earn recalls to the replacement bench along with prop Taufa’ao Filise who is set to claim legendary status at the region.
If Tongan ace Filise comes off the bench he will make a record-breaking 183rd
appearance for Blues, putting him clear in the all-time appearance charts.
Mark Hammett said: “We’re all looking forward to the game and the battle of ‘East versus West’.
“It will be a new experience for me and my first taste of a festive Welsh derby. But I’ve heard all about the big crowds and the fantastic atmosphere these games generate. We now need to harness that emotion and energy to help us perform.
“Scarlets secured an impressive European win over Ulster Rugby last weekend and are powerful side that plays with real aggression,” he added.
“They like to pin you back and create pressure. They also have real line speed in defence and are physical around the contact area.
“We’ve got to be ready to meet that challenge head on because we know how crucial a win could be for our league campaign and aspirations of climbing the table.”
Tickets remain on sale NOW for our big festive fixture with Scarlets at BT Sport Cardiff Arms Park. Call the
Ticket Office on 02920 302030 or click on www.cardiffblues.com/tickets to take your seat.
Cardiff Blues: 15 Joaquin Tuculet, 14 Alex Cuthbert, 13 Cory Allen, 12 Adam Thomas, 11 Lucas Amorosino, 10 Gareth Anscombe, 9 Lewis Jones; 1 Gethin Jenkins (c), 2 Kristian Dacey, 3 Adam Jones, 4 Filo Paulo, 5 Lou Reed, 6 Josh Turnbull, 7 Sam Warburton, 8 Josh Navidi
Replacements: 16 Matthew Rees, 17 Sam Hobbs, 18 Taufa’ao Filise, 19 Macauley Cook, 20 Manoa Vosawai, 21 Tavis Knoyle, 22 Gareth Davies, 23 Tom Isaacs