Forensic scientist Nighean Stevenson told the jury at the High Court in Glasgow the chance of the blood belonging to anyone else is a million to one.
Dr Stevenson was giving evidence at the trial of Colin Coats, 42, David Parker, 38, Paul Smith, 47, and Philip Wade, 42.
All four deny abducting, torturing and murdering Miss Spence at a flat at Meadowfoot Road, West Kilbride, between April 14 and 28, 2011.
Miss Spence went missing on April 14, 2011.
Dr Stevenson told Solicitor General Lesley Thomson, prosecuting, a DNA sample was taken from one of Miss Spence's metal bangles.
The court heard the DNA obtained from the bangle was compared with that of Miss Spence's parents Jim and Patricia.
Dr Stevenson said: "The DNA sample taken from the bangle was consistent with her being a daughter of Mr and Mrs Spence.
"She was their only daughter. Therefore it is assumed to be the DNA profile of Lynda Spence."
The forensic scientist said she examined the flat from October 28, 2011, and took swabbings.
She was asked by Miss Thomson about a blood swabbing taken from linoleum near the bath.
Dr Stevenson said: "The probability of finding someone else matching that DNA profile is more than one in a million."
The trial continues.