Someone from the lab is not enough, the Supremes let the country know today in their opinion in Bullcoming v. New Mexico (PDF File). In 2004 the Supreme Court decided Crawford v. Washington which began the current jurisprudential consideration (in about 25 years) of the Confrontation Clause of the United States Constitution, which is part of the 6th Amendment and states that "the accused shall enjoy the right to . . . be confronted with the witnesses against him." In Crawford the Supreme Court said that a tape recording could not be used in evidence against a criminal defendant, because the tape recording could not be cross examined.
In Melendez-Diaz v. Massachusetts, the prosecution entered into evidence a laboratory certificate which indicated that suspected narcotics were tested and confirmed to be cocaine. The Defendant objected at trial that under Crawford the certificate could not be introduced without the laboratory analysts testimony and the defendant's ability to cross examine him. While the state courts found for the government, the Supreme Court of the US, in 2008, ruled that the state does have to produce the lab analyst at trial, because the lab certificate is testimonial in nature and thus covered by the Confrontation Clause.
Most states operated in the same method as Massachusetts before Melendez-Diaz was decided, in that suspected drugs were sent to a state lab, analyzed and a certificate was sent back to police with identification and weight of the drugs. This certificate was later admitted into evidence at trial to prove the substance seized from the defendant was illegal drugs.
After Melendez-Diaz, states scrambled to come into compliance with this new ruling, or else face dismissal of many drug and DUI charges because of this new barrier to admission into evidence the nature of the drugs (or blood alcohol level, which undergoes a similar analysis for blood analysis). In Virginia prosecutors adopted a number of policies that ensured that every defendant received notice of his ability to object to the presence of an analysts, and the law was changed to require notice and objection by the defendant or else the objection be waived. The legislature responded with changes to section 19.2-187 and the addition of 19.2-187.1.
Today, in Bullcoming, the US Supremes define the confrontation clause even further. Bullcoming was a DUI case where the defendant refused a breath test and was compelled to give a blood sample instead. The blood sample was analyzed by the state lab for alcohol content, the certificate produced and a representative from the lab appeared to testify at trial. However the person who appeared to testify was not the same person who actually tested the sample, and did not witness the test being performed. The Supremes voted no in a 5-4 decision, stating that the Confrontation Clause does not lend itself to exceptions or deviation, but instead the court supported the notion that the Right of Confrontation was a bright line rule. Justice Ginsburg states the matter better than I am able, where she writes "the analysts who write reports that the prosecution introduces must be made available for confrontation even if they possess “the scientific acumen of Mme. Curie and the veracity of Mother Teresa."
From the Bullcoming ruling comes the hint that the Court may approve of entry of such a certificate if the analyst was unavailable and the defense had enjoyed a previous opportunity to cross examine the witness in an earlier proceeding. Further, as New Mexico requires preservation of laboratory samples, the state could have simply had the sample re-tested by the analyst who was able to appear in court.