Clinical samples from patients?

Question

I was just wondering what are some ways a clinical sample can be contaminated from the time it is taken from the patient to the time it is analyzed in the laboratory...

Answer 1

The main "contaminant": is improper collection. Years ago all laboratory blood samples were collected by highly trained medical technologists. Then phlebotomists were trained to do this while the techs remained in the laboratory. Then nurses were assigned this task. Nurses receive very little training in specimen collection. It isn't their fault that they mess up because they are now assigned a critical task with inadequate training - but it is very frustrating for them and those in the laboratory. How many nurses know the proper order of draw and why it is important???? Each tube either contains a special anticoagulant or has no additive. Any anticoagulant left on the needle can contaminate the following tube so it is very important that each color tube be filled in correct order. It is also very very important to never ever draw above an IV and best to avoid the arm with an IV or IV fluid can contaminate the tubes. Nurses often like to use the IV line for blood drawing - they may pull a bit of blood first thinking they are clearing the line, but often some contaminating fluid remains. Especially a problem when heparin in the line contaminates a test for coagulation lab. Leaving a tourniquet on too long will also contaminate a lab specimen. Another common "contaminate" that we see daily is when a nurse draws the samples and then doesn't fill all the tubes and then transfers some blood from the purple top tube and puts the blood in the green top tube. The purple top tube contains potassium, so when we run the green top tube and get a potassium level outside the normal range (patient would be dead if the result was correct) we know the nurses are messing with the test tubes again. But the number one concern of all laboratory professionals is specimen labeling. It is not uncommon to discover samples that do not belong to the name on the label. If a hospitalized patient has a dramatic change in results form one day to the next that is what we always suspect and we are almost always right. Strange how a patient's blood type can change from O pos to B pos! Actually- blood types do not change but that is one of the ways we prove that the wrong patient was drawn. My pet peeve is when samples are drawn and left unlabeled for hours and then labeled later. All samples - each and every tube should be labeled at the patient's bedside. I wish that nursing understood how important this is.
Another "contaminate" is improper specimen handling - not mixing each tube as it is drawn and then the anticoagulated tubes clot. Once clotting starts in a tube with anticoagulant the specimen is no good. Removing the clot alters the specimen and it is still no good. Once a specimen is anticoagulated it remains anticoagulated and will not clot for days and days. Many times when there is a specimen collection problem, the nursing staff blames it on the lab rather than fessing up to the problem. This makes patients lose confidence in the laboratory.
Other "contamination" problems are hemolysis - from too much force applied to the specimen during collection or excessive mixing, delay in delivering specimen to the lab, and last but definintely not least - improper arm preparation and contaminating blood cultures with skin bacteria.

sorry - you hit a nerve. :)

Answer 2

the answer is always yes! It depends what the result says. For every sample there is "usual contaminants." What type of sample and what is the finding? Ask the doctor if they think it's a contaminant