October 23, 2020MaryBeth DiDonna
Cindy Brawley, MT(AMT), MHA, is the US diagnostic product manager at SARSTEDT, Inc. She previously worked as a senior medical technologist, and later as community operations and strategy manager for the outpatient healthcare system at Children’s Healthcare Atlanta.
Q: What are the consequences of hemolysis in patient samples?
A: Hemolysis can lead to biased results, and it can possibly cause misdiagnosis, incorrect patient treatment, or lack of treatment. Just 5 percent hemolysis can raise a potassium level from 4.0, which is normal, to 7.0, which generally requires treatment. It can lead to misdiagnosis because if the patient has a low potassium level and the sample is hemolyzed, it could generate a normal result, and treatment isn't provided for that hypokalemic state.
Q: How do you know when you have a hemolyzed sample in the laboratory?
A: In chemistry testing, you centrifuge the blood to separate the cells from the plasma or serum. Hemolysis occurs when the red blood cells rupture and release hemoglobin into the plasma or serum, most often occurring during the preanalytical testing phase. You can visibly see a red color from the hemoglobin in the plasma or serum, and most laboratory chemistry analyzers can measure the hemolysis level. When the hemolysis level interferes with the reporting of the measured analyte, like potassium, an instrument indicator will flag the affected analyte results. Many laboratories also have middleware that prevents erroneous or flagged results to cross into the patient’s electronic health record, preventing a misdiagnosis or treatment. A recollection of the specimen is necessary to ensure a quality specimen is tested and reported.
Q: How do you know that hemolysis has occurred in point-of-care testing?
A: With point-of-care testing, you don't know the sample is hemolyzed because it's whole blood. You don’t see the plasma or serum separated from the cells, so no visual cue, and there are no hemolysis indicators in POC instruments. If the blood is hemolyzed and the result goes directly to the patient’s electronic health record, the result is there. Neither the collector nor the doctor has any idea that the specimen was hemolyzed. If the clinical picture doesn't fit, testing must be repeated in the laboratory. Sometimes you cannot tell by the clinical picture that there was a blood specimen quality issue.
Q: What can be done to identify hemolysis in point-of-care testing?
A: A wide variety of people perform point-of-care collections. Nurses, respiratory therapists, phlebotomists, and medical assistants in both doctor's offices and hospitals collect and perform point-of-care testing. How can we standardize that process? It’s important to set parameters for confirming your point-of-care testing quality by doing side-by-side testing regularly in the laboratory to identify pre-analytical errors that may occur during the collection phase.
The tools used to perform blood collection and the process for dosing point-of-care cartridges could be the root cause of poor-quality specimens. A common practice is to collect blood from the patient’s line using an evacuated tube, and then transfer the blood to the POC cartridge using a disposable transfer pipette; both steps can introduce shear force resulting in hemolysis. It can also be challenging to properly dose POC cartridges using a transfer pipette. Common problems like over-filling, under-filling, and bubbles can cause an error code and no result. The test must be repeated, and the cartridge wasted.
SARSTEDT developed a point-of-care kit with these challenges in mind. It includes an anticoagulated S Monovette® tube to collect blood by venipuncture or from an IV catheter using a gentle aspiration technique that minimizes the shear force on red blood cells and thus the threat of hemolysis. The syringe-style tube collects a low collection volume of 1.1 milliliter of blood. A dosing tip is then attached, and the POC cartridge is dosed by using a slight turn of the piston to expel blood into the cartridge. It is a totally closed system<em-dash>no opening of tubes full of blood<em-dash>minimizing exposures to blood.