Understanding Your Lab Results: Normal vs. Optimal Ranges & What They Mean
- Melissa Nichols
- Jul 19
- 4 min read
Updated: Aug 13
Laboratory test results drive approximately 70% of clinical decisions, making them a crucial component to understand. Ever been told your labs were normal, but you still felt off? You're not alone. Many people walk away from routine bloodwork frustrated, knowing something doesn't feel right.
The truth is, there's a difference between being "within normal limits" and being in an "optimal range" for health. Let's dive into what your labs are saying and how to interpret them more meaningfully.
What Are Laboratory Reference Ranges?
A reference range is the set of values that 95% of a healthy population falls into. The population considered suitable for blood donation is generally considered healthy, and specimens from this population are often used to determine normal reference ranges for lab test results.
Under ideal circumstances, each laboratory is expected to determine its normal reference ranges by testing at least 120 individuals without discernible disease, from each relevant age, gender, and ethnic group in the population served by the lab.
But here's the catch:
These values represent population averages, not necessarily ideal health.
This "healthy population" may include people with early signs of disease or
poor lifestyle habits.
You can fall within the "normal" range and still experience symptoms or risk factors.
This is where optimal ranges come in.....
Normal vs. Optimal: What's the Difference?
Lab Test | Normal Range* | Optimal Range* |
Fasting Glucose | 70–99 mg/dL | 75–85 mg/dL |
Vitamin D (25-OH) | 30–100 ng/mL | 50–80 ng/mL |
TSH | 0.4–4.0 mIU/L | 0.5–2.0 mIU/L |
CRP (hs-CRP) | <3.0 mg/L | <1.0 mg/L |
*These ranges can vary slightly depending on the lab
Normal Range = you're unlikely to have acute disease
Optimal Range = your body is functioning at its best, and there's a reduction in your risk for chronic disease
What Are Conventional & SI Units?
Lab results are reported using either conventional units or SI units (International System of Units), depending on where you live and the lab's standards.
Conventional Units (U.S. standard):
Example: Glucose is measured in mg/dL (milligrams per deciliter)
SI Units (global standard):
Example: Glucose is measured in mmol/L (millimoles per liter)
To convert:
Glucose: 1 mmol/L = 18 mg/dL
Cholesterol: 1 mmol/L = 38.67 mg/dL
👉 Always pay attention to the units when reviewing international lab results or online references. Also, if you have your blood drawn at different labs, you may need to convert the results before comparing them. There are many conversion calculators online.
What Influences Reference Ranges?
Normal values reported by the testing laboratory are derived through a process with many assumptions, differences in methods or expert opinion, and other sources of variation in results. For example,
(a) blood levels of creatinine kinase, a muscle enzyme, go up with normal
activities;
(b) blood levels of alkaline phosphatase are higher after a meal.
This emphasizes the importance of following the direction of your health care provider when preparing for a blood draw.
Several factors affect what is considered "normal" on a lab test:
Age
Laboratory results can vary by age. Some examples are:
A child's normal alkaline phosphatase levels should be higher than an adult's.
Postmenopausal women naturally have lower estrogen levels.
Gender
There are differences in some reference ranges by gender. Hormones play a role in this. The reference ranges for non-binary/transgender people are still being worked out.
Ethnicity
Some laboratory values differ by ethnicity.
One reference value
Some analytes only have an upper-level range. This includes blood creatinine, where values over the upper reference range indicate kidney insufficiency.
Method of testing
Test results and normal values vary by the method of testing.
Variation by Laboratory
There is additional variation in results among laboratories using the same methods and instruments, including for lab assays that have undergone harmonization. The variability in repeat testing per laboratory is narrower, encouraging the use of the same laboratory for serial monitoring of a given assay.
Fasting vs. non-fasting
Fasting status directly affects glucose, insulin, and triglyceride levels.
According to the Journal of the American Board of Family Practice, lab ranges should always be interpreted within the full context of the patient, including their medical history, physical examination, and individual risk factors. Results should always be reviewed with your physician.
Personal Experience
I have personally experienced how the differences in lab ranges can impact the standard of care. A short while ago, my TSH levels were 3.14 at my primary care physician's office. I had symptoms of weight gain (which was unusual for me), and I was feeling bloated. My doctor took no action as this value was within the normal range. I then went to my functional medicine doctor for a second opinion. She noticed my TSH was not within the optimal range and did additional testing. It turns out that I had hypothyroidism. Once I went on a low dose of medication, I felt better, and my weight normalized.
What This Means for You
Being told your labs are “normal” doesn’t always mean you're healthy. If you still have symptoms like fatigue, low libido, weight gain, or poor sleep, it’s time to dig deeper. Seek alternative options to get answers. Nobody knows your body like you do.
Final Thoughts
Understanding the difference between normal and optimal lab values puts the power back in your hands. It helps you ask better questions, seek better care, and make informed choices about your health.
If you’ve been feeling off but your labs are normal, trust your instincts. You deserve clarity, not confusion.
Need help making sense of your labs? Check out the resources section of my website for optimal ranges and reference links. www.reformingyou.com
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