In writing a procedure, I strive to make it the reference on the bench. Yet no matter how good a written procedure is, the package insert is always invaluable.
There are two reasons for this. One, the package insert is the main reference for any procedure and should be consulted to resolve questions. This can be useful if information changes, for example. Two, there are details in the package insert that may not be included in a stepwise procedure meant to standardize performance on the bench.
I'll use a urine pregnancy test package insert as an example. A common question is, "How soon after conception is the test positive?" Unless explicitly stated in a procedure, the package insert becomes the reference. Under "Limitations" there are the following statements:
- Very low levels of hCG (less than 50 mIU/mL) are present in urine specimen shortly after implantation…
- A number of conditions other than pregnancy… cause elevated levels of hCG…
- The test provides a presumptive diagnosis for pregnancy.
"Sensitivity and Specificity" claims the test will detect as little as 25 mIU/mL in urine, but "Expected Values" reminds us that the amount of hCG will vary with gestational age and between individuals.
Other details include storage and stability of the specimen, collection technique, presence of particulate matter, the condition of the reagents, and cross reactivity of substances or chemicals in the urine. What seems like a simple question quickly becomes complicated. The real question is, is there an answer?
While package inserts are invaluable for details, they may not answer simple questions well. This is where a stepwise procedure can help. A statement such as "Repeat in 48 hours on a first morning void to confirm equivocal or weak positive tests" can help. Package inserts often remind us that a single laboratory test result is only one piece of the puzzle.