Shares of Quest Diagnostics ( DGX) sank 3% Thursday after the lab specialist guided lower for 2007. The diagnostic test outfit earned $151 million, or 77 cents a share, in the fourth quarter, vs. $149 million, or 73 cents a share, in the year-ago period. Analysts surveyed by Thomson First Call expected Quest to earn 74 cents a share. Revenue grew 8.5% to $1.55 billion, thanks in part to Quest's acquisition of LabOne in November 2005 and Focus Diagnostics in July of last year. Analysts expected revenue of $1.57 billion. For 2007, the company expects earnings of between $2.70 and $3 a share on $6 billion to $6.2 billion in revenue. Analysts were expecting earnings of $3.21 a share on sales of $6.4 billion for the year. Quest's 2007 estimates reflect reductions related to the anticipated impact of contract changes, the company said in a press release Thursday. Last October, huge insurer UnitedHealth ( UNH) dropped Quest in favor of rival LabCorp ( LH), saying LabCorp was cheaper. Shares fell $1.58 to $49.48.