Updated from 1:59 p.m. EDT

Quidel ( QDEL) was easily the worst-performing health care stock Friday after the San Diego diagnostics company warned that second-quarter results would fall well short of expectations.

Instead of reporting a profit, Quidel now expects to report a loss of 12 cents a share on sales of $14.3 million. Analysts polled by Thomson First Call had expected earnings 2 cents a share on sales of $20.8 million. The company said unanticipated confusion surrounding intellectual property litigation led to "disappointing" Strep A orders and weaker-than-expected second-quarter sales. Shares of Quidel traded down $1.77, or 33.8%, to $3.46.

Shares of CTI Molecular Imaging ( CTMI) slumped after the maker of medical scanners warned that third-quarter numbers wouldn't meet guidance. Instead of earning 8 cents to 10 cents a share, CTI now expects to earn 2 cents to 4 cents. Revenue, meanwhile, is now expected to be $85 million to $90 million, well short of the previous guidance of $95 million to $100 million. Analysts had expected the company to earn 10 cents a share on sales of $98.5 million. The company attributed the weak results to fewer scanner shipments in the quarter. Shares of CTI Molecular traded down $1.37, or 10.2%, to $12.

A day after gaining nearly 6%, shares of Cantel Medical ( CMN) gave back all of their gains and more on Friday. Shares of Cantel rose Thursday after its subsidiary, Minntech, received Environmental Protection Agency clearance for the use of its Minncare cold sterilant, which is used to disinfect ultrapure water production and distribution systems used by kidney dialysis centers, pharmaceutical manufacturing companies and the microelectronics industry. Shares of Cantel Medical traded down $2.11, or 8.1%, to $24.

Abbott Laboratories ( ABT) fell modestly after the drugmaker reported in-line second-quarter earnings and better-than-expected sales. Excluding several items, it reported earnings of 54 cents a share on sales of $4.7 billion. Analysts expected the company to report earnings of 54 cents a share on sales of $4.58 billion. Looking ahead, however, Abbott said third-quarter earnings would be between 51 cents and 53 cents a share. Analysts had expected earnings of 54 cents a share. Shares of Abbott Laboratories traded down 38 cents, or 0.9%, to $39.90.

Other health care volume movers included Pfizer ( PFE), up 6 cents to $34; Amgen ( AMGN), up 29 cents to $53.61; Genentech ( DNA), down 65 cents to $51.35; Schering-Plough ( SGP), up 25 cents to $18.07; and Johnson & Johnson ( JNJ), up 23 cents to $54.99.