California Code, Evidence Code - EVID § 712

Notwithstanding Sections 711 and 1200, at the trial of a criminal action, evidence of the technique used in taking blood samples may be given by a registered nurse, licensed vocational nurse, or licensed clinical laboratory technologist or clinical laboratory bioanalyst, by means of an affidavit. The affidavit shall be admissible, provided the party offering the affidavit as evidence has served all other parties to the action, or their counsel, with a copy of the affidavit no less than 10 days prior to trial. Nothing in this section shall preclude any party or his counsel from objecting to the introduction of the affidavit at any time, and requiring the attendance of the affiant, or compelling attendance by subpoena.