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CHICAGO — Baxter International Inc. says two kidney patients in Texas who underwent treatment on dialysis machines using Baxter filters have died and two others were hospitalized with complications. 

The U.S. Food and Drug Administration, which oversees the manufacture and distribution of medical products, is investigating the cause of the deaths. 

“We are in the process of looking into it,” spokeswoman Sharon Snider said Thursday. 

Baxter on Wednesday announced a worldwide recall of its Series A and Series AF dialyzers which are manufactured in Sweden by Althin Medical AB, acquired by Baxter last year. The devices filter waste substances from the blood before it is returned to patients with kidney failure. 

The A series of dialyzers were used in Croatia, where authorities blame the dialyzers for the deaths of 23 kidney patients earlier this month, and in Spain, where 15 patients reportedly died in August at health centers while undergoing kidney dialysis. 

The filters used in connection with the Texas deaths were of the AF series. Both series use a similar fiber. 

Baxter said it is not clear what role the filters played in any of the deaths. 

“There is no information linking these deaths to the dialyzer made by Baxter,” spokeswoman Tanya Tyska said. “We’ve instituted the recall as a precaution until an investigation into all aspects of their treatment is completed.” 

“It’s unusual. We haven’t seen this with dialysis membranes before causing widespread death like this,” said Dr. Paul Scheel, dialysis director at Johns Hopkins Medical Center. “The dialyzers are a relatively new brand for Baxter and that certainly raises some uncertainty about what the potential interaction between the blood” and the dialyzers could be. 

Baxter has sent investigators to Texas, Spain and Croatia. The company has not released the names of the Texas patients, nor the hospital in which they were treated. 

Tyska said one of the two hospitalized kidney patients has been treated and released. 

Dialyzers are hollow filtering tubes that are attached to dialysis machines, which clean impurities from blood of patients with kidney failure.  

Blood is drawn from the patient’s vein and pumped through the dialyzer, where impurities are filtered into a special fluid called dialysate, which mixes with water to flush the impurities away. The patient’s blood is then pumped back into the body. 

Tyska said potential causes of adverse reactions could occur at any point in the process because of inadequate water treatment and quality, contaminated dialysate concentrate, machine malfunction, clogged blood lines and needles, and the medication administered before and during the process. 

“The investigators might look at all these possible causes of adverse events,” Tyska said. 

In Zabreb, Croatian Health Minister Ana Stavljenic-Rukavina said the filters are suspected in the deaths because all the victims were treated using them and deaths dropped to normal levels when hospitals replaced the filters with other brands. A panel of experts is investigating. 

In Spain, an investigation by a European quality standards firm found no link between the deaths and filters, although the Spanish government is still running tests. 

The Texas Department of Health hasn’t received any complaint that would prompt an investigation. 

“We haven’t received any complaint or any question from any hospital or facility,” said department spokeswoman Emily Palmer. 

Baxter is a global medical products and services company that provides therapies for people with life-threatening conditions.