A new shortage of a key testing component is hobbling the U.S. battle against COVID-19 as the number of confirmed coronavirus cases continues to rise. 

Earlier testing was marred by problems that produced potentially inaccurate results. Now, as U.S. testing ramps up, some labs have run short on the kits and components needed to determine whether samples taken from ailing patients confirm the presence of the novel coronavirus.

The problem is emerging as the number of confirmed COVID-19 cases in the U.S. rose to above 1,000 as of Wednesday, with 28 deaths, according to Johns Hopkins University.

In some cases, the shortage has prompted lab personnel to borrow components from colleagues who were using similar kits for testing unrelated to COVID-19, said Marc Lipsitch, a Harvard University epidemiologist. The extent of the problem could not immediately be determined.

"What we need is a lot more testing, right now," Lipsitch said, but testing kits and components "are in very short supply."

Some of the testing components are manufactured by Qiagen, a multinational leader in molecular testing headquartered in Germany. Spiking demand for its products has prompted the company to increase production to three shifts a day, seven days a week, at plants in Germany and Spain.

"This now is an unprecedented situation," said Qiagen corporate spokesman Thomas Theuringer. "Demand is exploding, especially in the United States ... and this is stretching our capacity."

Michael Mina, a Harvard professor of epidemiology, tweeted Monday that the testing components are critical.

The shortage results in part from the recent increase in COVID-19 testing across the U.S. after a slow start due to problems with testing kits from the U.S. Centers for Disease Control. State and local health officials responded by calling on the federal government for authorization to use tests they developed. That began in many places over the last week.

Now testing is being done by health departments and clinical diagnostic laboratory giants such as Quest Diagnostics and Laboratory Corporation of America.

Testing for coronavirus typically uses reagents, which are substances used in chemical analyses. The reagents extract, purify and stabilize RNA, or ribonucleic acid, in samples taken from patients suspected of having COVID-19.

That's the first step in confirming or ruling out a tentative diagnosis. Qiagen says it leads the world in this type of testing.

However, testing demand has led to a shortage of reagents for the RNA extraction process, said Dr. Eric Blank, the chief program officer for the Association of Public Health Laboratories, which represents state and local governmental health laboratories in the U.S. and responds to disease outbreaks.

"We are now in the phase of the response where demand for testing is greater than the tests available, even when the private/commercial sector is doing testing," Blank said in an email.

The Association of Public Health Laboratories is working with member labs and the Centers for Disease Control to understand how the shortage will be addressed, Blank said.

Along with increasing its production, Qiagen is hiring more employees and increasing manufacturing at a facility in Germantown, Maryland.

"Given our ongoing supply to the United States," Theuringer said, "we are now working directly with the customers to understand their flexibility and specific needs in order to be able to ensure broad availability of our products."