“Oxy” cleaners may make forensic tests, such as this one checking a shoeprint for blood, ineffective.

Criminal investigations begin with a search for clues. Teams of investigators arrive at a crime scene armed with special fact-finding gear. They look for standard evidence like fingerprints, footprints or blood at the scene of a crime.

But scientists recently discovered something troubling. Some new household cleansers can remove all traces of blood. If criminals simply use these products to clean up after themselves, police may have a hard time gathering evidence.

To get at particularly stubborn stains, like an accident from your pet, your parents may use one of these new products called “oxy” cleaners. These cleansers use oxygen and water to attack stains, including blood. Some of the ads claim to clean “over 101 stains on multiple surfaces.” That sounds good, but scientists have identified a downside to that much cleaning power.

The oxy cleaners even go beyond getting rid of visible stains. Usually detectives’ gear can find traces of blood that are invisible to the naked eye. But these oxy cleaners make even the invisible traces of blood unrecognizable to the most common blood-detecting tests.

The three standard tests for picking up blood rely on a protein in the blood called hemoglobin. This protein loves oxygen. In the body, it’s hemoglobin’s job to grab onto oxygen and carry it from the lungs to the rest of the body. But the new oxy cleaners flood a blood stain with a lot of oxygen. Once the protein gets its fill of oxygen, it won’t even bother to snatch oxygen from the investigators’ blood detecting tests. This means these tests will come up negative.

When you scrape your knee, a nurse, parent, or coach may rub it with hydrogen peroxide. Hydrogen peroxide contains hydrogen and oxygen and helps stop the bleeding. The chemical causes oxygen that looks like foam to rise to the surface of your cut. There, too, hemoglobin in your blood seeks the oxygen in the hydrogen peroxide.

Common blood detectors rely on the same kind of reaction between blood’s oxygen and hydrogen peroxide. The detectors contain hydrogen peroxide that reacts with hemoglobin in a blood stain. When hemoglobin grabs some oxygen, the blood detecting test gives a positive result. Depending on the chemical in the test, a positive result might glow or turn pink.

In the name of science, a group of researchers decided to test the oxy cleaners. The scientists made their own fake crime scene by using samples of their own blood to stain a couple pieces of cloth. The team put five drops of their own blood on a soft cotton cloth, some jeans and a towel.

Then, the researchers washed part of each cloth sample in “Neutrex,” an oxy cleanser. The team thought the oxygen in Neutrex would be released upon contact with water. The large amount of oxygen would cause the hemoglobin to work overtime. This would effectively clean up the blood, but also tire out the hemoglobin so that it wouldn’t react with the tests. The scientists also washed other samples of blood-stained cloths with a traditional cleaner. All the samples were then left to air dry.

The cleaners worked as the scientists suspected. The cloths washed without oxy cleaners looked clean, but the three tests still picked up the blood traces. But after an oxy wash, the other sample fabrics looked spotless to the naked eye, and also came up clean on the blood tests. The difference: The oxygen bath given to hemoglobin exposed to the oxy cleaners. After spending time in the presence of that much oxygen and trying to snatch it, the hemoglobin couldn’t react with the investigators’ tests.

Despite the study’s results, this cleaning possibility doesn’t mean that bloody crime scenes are a thing of the past. “People committing violent crimes often don’t have time to clean up; they leave a lot of stuff behind,” says Walter Rowe, a forensic scientist, someone who examines evidence in a legal case, at George Washington University in Washington, D.C.

But how long can blood be safely stored before it’s no longer any good? Today, the government says hospitals can hold it for 42 days before it’s considered too old. The average age of blood used in transfusions is about 15 days. But new research shows even 15-day-old blood might be past its prime.

The blood stored in these bags can save lives—but its useful shelf-life is shorter than researchers had realized.

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Blood performs a crucial role in our bodies. It transports oxygen and other nutrients to cells and hauls off waste from those cells.

Previous research has shown that blood changes while it is in storage. But no studies had teased out whether these changes affect the people who receive the blood. In a new study, scientists at the Cleveland Clinic in Ohio examined hospital records of 6,002 people who received a transfusion of red blood cells after heart surgery. (Red blood cells carry and deliver oxygen around the body.) Almost half of the patients had been given new blood, less than 14 days old, and a little more than half had received blood older than 2 weeks. The scientists tracked the health records of the patients to check for any other differences.

By following what happened to the patients after the surgery, the scientists found that those who received the older blood had a higher chance of some serious problems. They were more likely to die in the hospital after the operation. Their kidneys didn’t function as well. They had more frequent occurrences of a blood disease called sepsis. And more of them died during the year after surgery.

Some changes in the blood might account for the health differences. Red blood cells that have been stored for too long start to lose the chemical that allows the cells to hand oxygen over to other cells in the body.

Also, scientists saw a difference in blood cell shape. After sitting in storage, cells link together to form long chains, “like miniature doughnuts stacked on one another,” says Eugene Blackstone, a doctor at the Cleveland Clinic. These doughnut-like chains might become too big to fit through capillaries, the smallest of blood vessels, and might therefore prevent the donated cells from reaching their targets.

The scientists caution that this study doesn’t give the final answer on the best storage time for blood. They say larger studies are necessary. But more than 5 million people in the United States receive blood transfusions each year. Studies such as this one may help those patients receive the healthiest blood possible.—Cynthia Graber

Power Words

From The American Heritage® Student Science Dictionary, The American Heritage® Children’s Science Dictionary, and other sources.

blood transfusion The transfer of blood from one person to another.

capillaries Tiny blood vessels that connect the smallest arteries to the smallest veins. Oxygen is delivered to, and carbon dioxide is removed from, the tissues of the body by means of the capillaries.

cells The most basic part of a living thing, made up of a jelly-like substance called cytoplasm that is enclosed by a thin membrane. The cells of plants and many-celled animals have a nucleus, which contains the genes and other structures.

oxygen A chemical element that is a colorless, odorless gas and that makes up about one-fifth of the Earth’s atmosphere. Oxygen is the most common element in the Earth’s crust, and it combines with other elements to form water, carbon dioxide, and iron ore. Oxygen is needed for plants and animals to live.

red blood cells A cell that is shaped like a disk and is found in the blood of humans and other vertebrates. Red blood cells contain hemoglobin, which carries oxygen to all the cells of the body and gives red blood cells their color.

Copyright © 2002, 2003 Houghton-Mifflin Company. All rights reserved. Used with permission.

Going Deeper:

Seppa, Nathan. 2008. Bad blood? Old units might be substandard. Science News 173(March 22):179. Available at http://www.sciencenews.org/articles/20080322/fob1.asp .

To learn more about blood transfusions, visit www.kidshealth.org/teen/your_body/
medical_care/transfusions.html (KidsHealth for Teens).

You can play a blood-typing game online at www.nobelprize.org/educational_games/
medicine/landsteiner (Nobel Foundation).

Seppa, Nathan. 2007. Stored blood loses some of its punch. Science News 172(Oct. 27):269. Available at http://www.sciencenews.org/articles/20071027/note12.asp .

Wang, Linda. 2001. Blood relatives. Science News 159(March 31):206–207. Available at http://www.sciencenews.org/articles/20010331/bob16.asp .