August 29, 2008
It seems innocuous enough—draw some blood, perform some tests and take a giant leap toward an accurate diagnosis. Just don’t forget about the potential red flags—even the ones that present as yellow or opaque.
Hemolysis, lipemia and icterus are three common endogenous interferants that can sabotage precise blood chemistry analysis. That’s true whether you perform blood work in-house our send out for analysis.
“All hematology is affected by sample-integrity issues, whether you have a $10,000 analyzer or a $150,000 one,” says Craig Tockman, DVM, director of professional services for Abaxis, a leading maker of point-of-care blood analyzers in Union City, Calif. Dr. Tockman also owns and operates two veterinary hospitals in St. Louis.
There are two overriding considerations when dealing with these interferences, experts say.
The first is to ensure your system provides an alert when hemolysis, lipemia and icterus occur at levels that threaten the dependability of test results.
The second key step is to employ clear and strict methods to prevent interferants from compromising otherwise reliable findings. Care in drawing, handling and storing blood should always be a primary consideration.
“A lot of it is education on the proper way to draw and to prepare samples,” Tockman says.
“We all get into habits, and not all of them are good. I’ve been in practices where 20-year-veteran technicians handle samples inappropriately and cause problems. If your staff turns over frequently or someone does things incorrectly and teaches others, you can be frustrated by results.
“All hematology is affected by sample-integrity issues, whether you have a $10,000 analyzer or a $150,000 one.”
—Craig Tockman, DVM, Abaxis
“I tell people that if you’re having excessive amounts of hemolysis, it’s probably not a sign of problems with your instruments; it’s probably a sign of a problem with the sample being analyzed.”
The time-honored first means for evaluating a sample is to examine it for endogenous substances. For instance, the presence of lipemia or fats in the sample can scatter light and cause opacity of appearance.
“It can be like trying to look through a milkshake,” says Karen Rosenthal, DVM, MS, chief of the Special Species Section for the Matthew J. Ryan Veterinary Hospital at the University of Pennsylvania.
Lipemia can be minimized by fasting an animal before blood collection, but it isn’t always easy to isolate an animal and be sure it hasn’t eaten, says Dennis Bleile, Ph.D., director of assay performance and compliance for Abaxis.
The indicator for icterus is the yellowing of the skin, mucous membranes and the whites of the eyes caused by an accumulation of bilirubin in the blood. However, “We really can’t eyeball how severe icterus is,” Dr. Rosenthal says.
As for hemolysis, the indelicate handling of the blood—using too much suction or forcing clotted blood from a syringe—can damage red blood cells, which leads to the release of hemoglobin.
But here, too, it’s not enough just to see red and think hemolysis, experts say.
“As with the presence of lipemia and icterus, a system that can show how much hemoglobin has been released from red cells is the key to getting results you can trust,” Bleile says.
“The system needs to determine the quality of the sample and either suppress the value or at least warn you that there might be an effect.”
Rosenthal says she has come to depend on the depth of information provided by her in-house laboratory system.
Her Abaxis VetScan VS2 blood chemistry analyzer measures each sample for hemolysis, lipemia and icterus, using algorithms generated by built-in software. The machine determines the level at which each substance will potentially interfere with the reliability of the results and alerts the user.
“The machine needs to be able to read analytes, and if there’s such a high degree of interference that it can’t make a determination, then the machine just won’t give a reading at all,” says Rosenthal, who is also interim medical director of the veterinary hospital at Penn.
No reading is many miles better than an unreliable reading, Rosenthal adds.
“Because the lab is in-house, I can find out in several minutes if the sample is compromised,” she says. “So before the client and the pet leave the hospital, I can say, ‘Let me repeat that test.’
As an expert in the treatment of exotics, Rosenthal draws clients from hundreds of miles away.
“The last thing I want to do is make someone use more gas to drive all the way back so we can repeat a test.”
It’s more than a matter of convenience, Rosenthal says. The reputation of the practice is on the line.
Of course, there’s also the matter of her own control issues.
“Being a control freak, I want to make sure my samples never leave the practice,” she says. “I want to know where the sample’s been and where it’s going at all times.”
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