3 Reasons Why Lab Tests Sometimes Lie

1. “Normal Ranges” aren’t “normal”. Having worked in a hospital laboratory for 20 years and being involved in setting “normal” ranges, what these ranges actually are is “average” ranges. That is, they’re an average of a set number of people who have been tested for whatever you are testing for. But, here’s the problem with doing that, you are making the very broad assumption that most of the people you are testing are normal. Are the majority of the people who end up in a doctor’s office or hospital perfectly normal, healthy people who are just wondering what their blood levels are like? No, they’re sick, and the doctor is ordering specific tests related to their sickness to determine why they might be sick. So, what labs do is average blood tests from unhealthy people to come up with a normal range!

2. Some lab values vary throughout the day, throughout the menstrual cycle, from one day to the next, sometimes one measurement isn’t enough to deem everything “normal”. Cortisol peaks in the morning and tapers to it’s lowest between 8 p.m. and midnight, measuring just a morning cortisol level, doesn’t tell you what is happening to cortisol throughout the rest of the day, at least a second measurement and preferably 4 measurements throughout the day is best. Progesterone isn’t produced until after mid-cycle ovulation and peaks about a week after ovulation, measuring it at any point other than a week post-ovulation or around day 21 in the cycle isn’t all that helpful. Prolactin is a hormone that enables breastfeeding and can suppress the ovaries, it can go up and down day to day depending on stress.

3. Equipment or operator error. Most blood tests are performed by complicated, computerized analyzers. Sometimes this equipment goes awry. If a lab value seems unusual, the operator should repeat it to confirm the value, but mistakes do happen and outliers sometimes get missed. Sometimes unusual values slip under your medical doctor’s radar too. No one is perfect.

What to do about it

1. Ask for copies of your blood work from your family doctor. Take it to someone who uses the optimal range to assess your results, rather than the “average of unhealthy people” range. At the very least, if you notice that one of your results is at either extreme of the normal range AND you are experiencing symptoms related to that particular test, bring this to your doctor’s attention. If he/she doesn’t have a solution, then bring it to a naturopathic doctor for ways you can be proactive about improving your lab values and get off the borderline.

2. Ask the ordering physician when the blood tests should be done – should they be fasting? first thing in the morning? later in the day? at a certain point in the menstrual cycle? is a one-off test sufficient, or should it be repeated a couple of times?

3. If a test is particularly abnormal or a big deviation from your normal, it should be repeated. It’s good to keep copies of your own blood work so that you can compare previous tests and see if there is a trend, such as your cholesterol was 3.20 last year and this year it’s 4.14, odds are that next year it will be close to if not outside the upper limit unless you are proactive about reversing it.

by Dr Pamela Frank, BSc(Hons), ND
Licensed Naturopathic Doctor with 30 years of experience with lab test interpretation

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