The Supreme Court avoided a major patent ruling Thursday, dismissing a case involving a test for diagnosing B vitamin deficiencies.

Justices split 5-3 in throwing out the case which had been argued this spring.

Chief Justice John Roberts recused himself because his old law firm represented Laboratory Corp. of America, a medical testing company that brought the appeal to the Supreme Court.

The court's action affirms a lower court judgment against LabCorp.

During arguments in March, justices struggled with broad questions of what can and cannot be patented.

Had the court found that a 1990 patent on a method of diagnosing B vitamin deficiencies covered a law of nature, the decision would have restricted the areas that are subject to patents.

Such an outcome would have had a widespread economic impact affecting claims in tens of thousands of older patents on drugs, medical devices and computer software.

Metabolite Laboratories Inc. and Competitive Technologies Inc., sued LabCorp after it stopped paying royalties.

LabCorp lost in the lower court and was ordered to pay about $5 million.

Under federal law, patents cover broad subject areas but can't be used for abstract ideas or laws of nature, such as Albert Einstein's theory on mass and energy or Sir Isaac Newton's law of gravity. But applying such a law of nature through a test or process can be subject to a patent.

LabCorp's attorney argued that the patent created a monopoly over a natural phenomenon and said the patent could be infringed by doctors who merely think about the relationship between B vitamins and homocysteine levels.

But Metabolite Laboratories insisted the patent makes use of a discovery as part of a diagnostic step.

The case is Laboratory Corporation of America Holdings v. Metabolite Laboratories Inc., et al., No. 04-607.