Real-Life Math

You're the head medical lab technologist working for a blood transfusion service. The level of responsibility in your job is high -- you ensure that the lab is running smoothly and efficiently.

Your lab runs tests daily, but today is going to be the real test of your clinic. It's January 31 -- the end of the month -- and it's your job to analyze the results of the month's tests or the "count" period.

By looking at the month's blood test results, you can hazard a guess as to how accurate your testing methods have been. If this month's tests show results well above or below the results of past months, then something may be wrong with the testing procedures.

You're going to start out by examining the accuracy of your lab's antibody tests. An antibody is the part of the immune system that combats disease. The lab runs tests on every patient's blood to see what antibodies are present. If the lab detects unusual or abnormal antibodies, this may help in the diagnosis of the patient's illness.

You have 3 methods of examining 2 tests.

In total, you have had 30 blood samples per day during the count period. Of the total blood samples you tested, 58 showed signs of foreign antibodies and you had to perform further tests for abnormal antibodies. If you have well above or below the average percentage of abnormal antibodies that you normally get, the testing procedure might be too sensitive or not sensitive enough.

For example, if they are well above the average amount of foreign antibodies this month, then your lab technicians are probably being too careful.

You also want to examine the efficiency of your procedures. Of the total samples, 25 had to be reinvestigated because of a faulty sample. In other words, something happened to the original sample so that your lab had to perform a re-test. If there are many more faulty samples than usual this month, then you need to be more careful when taking and handling the samples.

You also have to perform a direct antigolbulin test, or DAT, on the abnormal antibody samples. It could mean that a patient's red blood cells are coated, if they test positive for a DAT sample. That means that their red blood cells are being destroyed, and it can lead to serious medical conditions. As with the initial test, if you get too many positive tests, then you probably have too sensitive a test. Of the cases, 53 tested negative for DAT, while 5 tested positive.

Count Period Guidelines

• No more than 7 percent of all blood samples should show foreign antibodies
• No more than 1 percent of all blood samples should have to be re-tested
• No more than 17 percent of abnormal samples should test positive for DAT

Questions

1. What percentage of the total samples did you have to test for abnormal antibodies? Was that percentage within the acceptable guidelines?
2. How good were your samples? Did you have to do too many re-tests?
3. Was the DAT test too sensitive? Were there too many positive DATs?

• Ready for the solution?