5 Things you need to know about blood testing
We all get blood tests, whether at our annual physical or from another company, but do we know what they mean? Here, Dr. Anjali Dsouza shares five insights to help you make sense of your results.
Blood tests are a standard part of our diagnostic arsenal, but few of us really know what to make of the numbers that come back beyond a simple "good" or "bad." The truth is that there is a lot of nuance in those results that---once you understand---can help you know what to think of your results, and have a more informed conversation with your doctor.
Dr. Anjali Dsouza, who founded the District Center for Integrative Medicine in Washington, DC, is a functional health practitioner who can spend more time with patients than the 12 minutes primary care docs typically have, so she can walk them through this nuance. Here's what she wants everyone to know when they get lab results back.
1. Most "abnormal" results might not mean what you think
Blood tests are incredibly sensitive to what you did in the 48 hours before the draw. This sensitivity means many concerning results may have simple explanations that don't require medical intervention.
"More than 50% of the time, if something is really out of range, that is kind of outside of the pattern that somebody has, oftentimes when we repeat it, it's normal the next time we check it," Dr. Dsouza explains.
Common factors that can skew results
- Exercise: Intense workouts can elevate inflammation markers like hsCRP for days. Dr. Dsouza recalls a patient whose hsCRP spiked to 8 after Orange Theory class---indicating serious inflammation---but dropped to 0.2 the following week.
- Supplements: Biotin, popular for hair growth, can make your entire thyroid panel appear abnormal if taken before testing.
- Dehydration: Can artificially elevate kidney markers like BUN, making healthy kidneys appear compromised.
- Stress and illness: Even minor viral infections can cause temporary spikes in liver enzymes or inflammatory markers.
- Timing: Hormones should be tested before 9 AM when they're at peak levels for accurate assessment.
Before panicking over an abnormal result, consider what was different about the days leading up to your test. Many "red flags" resolve completely with proper retesting.
2. "Normal" ranges are designed for population averages, not optimal health
Laboratory "normal" ranges encompass 95% of the tested population---but that population includes people with undiagnosed illness, poor lifestyle habits, and suboptimal health.
"If you consider the fact that we also have sick people in the population, we're going to have a much larger range of what's considered acceptable," Dr. Dsouza notes. These ranges might keep you out of the hospital, but they won't necessarily help you feel your best.
For example, TSH (thyroid-stimulating hormone) typically has a reference range of 0.4-4.5, but Dr. Dsouza prefers to see it between 0.9 and 2.5, especially for women experiencing fatigue or weight gain.
The key is grounding everything in how you actually feel. Someone might thrive with a B12 level that would leave another person brain-fogged and exhausted. If you're experiencing symptoms but your labs are "normal," it may be worth exploring whether your numbers are optimal for you specifically.
Dr. Dsouza often contracts reference ranges by about 30% when looking for optimal rather than just adequate levels, but always correlates this with clinical symptoms.
3. Your blood work reflects your lifestyle choices
"I like to think about the gut as a muscle," Dr. Dsouza says, but the same principle applies to all your biomarkers. Your blood reflects what you've been doing consistently, not what you did once.
This creates both opportunity and responsibility. You can see improvements in weeks or months, not years, but they disappear just as quickly if you revert to old patterns.
Different markers respond at different speeds
- Quick responders (2-6 weeks): Glucose, insulin, triglycerides, some nutrients
- Moderate responders (2-3 months): Inflammatory markers when underlying causes are addressed
- Slower changers (3-6 months): Cholesterol (more genetic influence), some hormones
As Dr. Dsouza puts it, your blood work becomes "a Polaroid photo of your choices." The habits you maintain day after day determine what those numbers look like, making lab work an excellent feedback loop for lifestyle changes.
4. Context and patterns matter more than individual numbers
As testing becomes more comprehensive, you'll encounter results that don't fit textbook patterns. Maybe your glucose and insulin don't follow expected relationships, or other markers seem contradictory.
Dr. Dsouza takes a practical approach: "I believe that our bodies are more complex than we understand." Rather than forcing results into neat categories, she looks for patterns over time and focuses on the clinical picture.
"I don't hang my hat on one laboratory value or two laboratory values that are out of range," she explains. Sometimes puzzling results resolve on their own by the third test. Other times, they reveal individual variations that don't indicate problems.
Key principles for interpreting results
- Look at trends over time, not single data points
- Ground everything in how you actually feel
- Consider the whole picture, not isolated markers
- Work with practitioners experienced in comprehensive testing
- Don't panic over values that don't fit expected patterns
Many factors affect blood tests beyond your health status---from lab handling errors (rare but possible) to individual physiological variations that don't match standard patterns.
5. Strategic additional testing can provide valuable insights
Standard annual physicals typically include a complete blood count, basic metabolic panel, TSH for thyroid function, hemoglobin A1C for diabetes screening, and sometimes urinalysis. These tests answer one primary question: do you have a diagnosable disease right now?
While these tests are valuable, they may not reveal how you'll feel tomorrow, whether you're headed toward illness, or why you're exhausted despite being "healthy."
If you're interested in expanded testing but cost is a concern, Dr. Dsouza identifies three additional markers that offer significant value for a modest investment (typically under $100 combined):
Fasted insulin: Catches insulin resistance years before diabetes appears on A1C tests. "I find dysfunction in this number pretty much every time I look at it," Dr. Dsouza says. "It's very rare, unless I'm working with someone in their early 20s, that I don't see some kind of rise in insulin."
hsCRP (highly sensitive C-reactive protein): Reveals chronic inflammation that could be driving unexplained fatigue, brain fog, or mood issues. When persistently elevated, it points to underlying problems worth investigating---from gut imbalances to chronic stress.
Vitamin D: Despite being crucial for immune function, bone health, mood, and hormone production, vitamin D testing has become less common as insurance companies reduce coverage. "I actually think there's so much you can help just by having a sufficient vitamin D level," Dr. Dsouza notes.
These three tests provide insights into metabolic health, inflammation status, and a key nutrient affecting multiple body systems---areas standard panels often miss.
Getting the most from your testing
Whether you stick with standard panels or pursue expanded testing, several strategies can help you get more actionable information:
Optimize your test preparation
- Fast as directed (usually 8-12 hours for metabolic panels)
- Stay well-hydrated, but don't overdo it
- Avoid intense exercise 24-48 hours before testing
- Take hormone tests before 9 AM when possible
- Continue your usual supplements (except biotin before thyroid tests)
- Note anything unusual---illness, stress, changed routine
Track your patterns
Regular testing allows you to establish your personal baseline and notice trends before they become problems. Dr. Dsouza recommends comprehensive panels every 1-2 years for healthy adults in their 20s-30s, annually for those over 40.
Work with knowledgeable practitioners
Standard primary care physicians may have limited time to interpret extensive lab panels. If you pursue expanded testing, consider working with functional medicine practitioners or asking your doctor to focus appointments on specific concerning areas.
Moving forward with confidence
The goal isn't to become obsessed with perfect numbers---it's to have the information needed to feel your best and prevent problems before they become serious.
Dr. Dsouza's approach centers on four foundational areas that blood work can help optimize:
- Sleep quality and stress management
- Movement patterns that build rather than break down your body
- Nutrition that supports rather than fights your metabolism
- Recovery practices that allow adaptation and growth
"Those four things are the first section of every treatment plan that I make for a patient," she explains, "to communicate how fundamentally important that is."
Your blood work provides valuable feedback, showing whether your lifestyle choices are moving you toward or away from optimal health. The numbers matter, but only to help you feel energized, clear-headed, and resilient for years to come.
Understanding how to interpret and act on blood test results empowers you to be a more informed participant in your healthcare, whether you're working within the constraints of standard medicine or exploring expanded testing.
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