A friend called me in a state of confusion. She said that one of her friends was diagnosed with intermediate stage breast cancer despite undergoing regular mammography. “Isn’t mammography supposed to detect breast cancer?” she asked. So why did the doctors miss my friend’s cancer?
I have previously said that none of the interventions we employ in medicine come with absolute guarantee. Similarly, the laboratory tests that we do are also not 100% fail-safe. Not all diagnostic tests are as accurate as we hope them to be. There are many factors affecting the degree of validity and accuracy of these test results such as:
• Inter-laboratory variability – different labs can produce different results.
• Intra-laboratory variability – different results on different days due to factors such as different person performing the test, use of a different brand of chemical to carry out the same test, lack of calibration of machines
• Reader or interpretation variability – interpretation of results often depend on the reader’s experience such as reading of x-rays or CT scans. The same results can be interpreted differently by different persons.
• The quality of machines or reagents used – old machines (x-rays, CT scans, MRIs, ultrasounds) though cheap, can produce substandard results
• The inherent flaws of a test – not all tests, no matter how seemingly accurate, high-tech or done at reputable centers will give 100% correctness and accuracy. Some tests are bound to miss a positive diagnosis while others can detect problems that are not really there.
Tips to Minimize the Flaws and Maximize Laboratory Results
• Make sure that you are going to reputable laboratories instead of fly by night labs which offer lower prices to lure patients
• As much as possible, stick to the same laboratory to allow to minimize inter-laboratory variability.
• When doing specialized tests such as mammography, CT scans, MRIs, etc, better inquire from your doctor whether you can go ahead with a certain diagnostic center of your choice other than where your doctor wants to have it done. Patients often scout for cheaper prices (there is nothing wrong with this but let us take a lot of caution)and find them in small diagnostic centers not knowing that the cheaper cost is because they are using outdated machines which do not provide the same accuracy as the more expensive ones and hospital-based labs do. (I’ve had patients go for cheaper CT scans or MRI’s only to have them repeated at more reputable centers because the results did not give us the information that we needed)
• For tests that are done in series or annually such as xrays, CT scans, ultrasounds, mammography, MRI, request for the same reader to interpret your results.