Your labs came back ‘normal.’ So why do you still feel off?
One of the most common frustrations we hear from patients is this: "My doctor said my labs were normal, but I still feel terrible."
We believe you!
That's because conventional lab ranges are designed to catch disease, not to optimize health. In functional medicine, we use tighter, evidence-based ranges to identify imbalances before they become diagnoses. Functional Medicine Physician Dr. Bobbie Sinha and Registered Dietitian Sarah Becker walk us through a few of the labs we prioritize, what they reveal, and the ranges we’re looking for.
1. Vitamin D (25-OH Vitamin D) Optimal range: 60–80 ng/mL
Dr Sinha: Vitamin D functions less like a vitamin and more like a hormone. It influences over 200 genes and plays a central role in immune regulation, mood, bone density, insulin sensitivity, and inflammation control. The conventional "sufficient" threshold sits at 30 ng/mL, but research consistently shows that health benefits become most robust between 60 and 80 ng/mL. Deficiency is strikingly common, especially in those who work indoors, live at higher latitudes, or have darker skin tones.
2. Ferritin Optimal range: 70–150 ng/mL (women) | 100–200 ng/mL (men)
Sarah Becker RD: Ferritin is your body's primary iron storage mechanism, and it is often not tested. Standard labs often don't flag low ferritin until it falls below 12 ng/mL, but fatigue, hair loss, cold intolerance, poor exercise recovery, restless legs, and brain fog can all appear when ferritin drops below 50. On the other end, elevated ferritin above 200 can signal systemic inflammation, insulin resistance, or iron overload — which carries its own serious risks. We want our patients in the middle of a healthy range, not simply "not deficient."
Before we ever recommend iron supplements, we want to understand why ferritin is low. Is it dietary? Gut imbalances and absorption? Heavy periods? Chronic inflammation? The answer changes everything. Start with food first: pairing vitamin C-rich foods with iron sources significantly improves absorption, and cast-iron cookware is an underrated tool. Red meat 2–3 times per week and lentils regularly can make a real dent.
3. Vitamin B12 Optimal range: 600–1,000 pg/mL
Dr Sinha: The conventional lower limit for B12 is often listed around 200 pg/mL, a threshold at which neurological symptoms may have already been present for some time. Functionally, we want levels above 600, especially for patients experiencing fatigue, numbness or tingling, mood changes, or cognitive fog. Those at highest risk include vegetarians and vegans (this can happen in meat-eaters too, especially those with low stomach acid), adults over 60, and anyone on long-term metformin or proton pump inhibitors (PPIs).
B12 is one of those labs where the standard range will give patients false reassurance. I also frequently order methylmalonic acid (MMA) and homocysteine alongside B12 — these functional markers tell us whether B12 is actually working at the cellular level, even if the blood level looks adequate. And when we supplement, form matters: I prefer methylcobalamin over cyanocobalamin, particularly for patients with MTHFR gene variants.
4. hs-CRP (High-Sensitivity C-Reactive Protein) Optimal range: < 1.0 mg/L
Sarah Becker, RD: hs-CRP is one of our most sensitive markers of systemic inflammation — and chronic low-grade inflammation, often completely silent, is now understood to be a root driver of cardiovascular disease, type 2 diabetes, Alzheimer's disease, autoimmune conditions, and accelerated aging. Conventional labs consider anything below 3.0 mg/L acceptable, but we want to see our patients below 1.0. Levels persistently above 2.0 warrant a serious conversation about diet, sleep, stress, gut health, and movement.
This is where food is genuinely medicine. Omega-3 fatty acids and antioxidant rich foods from fatty fish (salmon, sardines, mackerel), extra virgin olive oil, colorful produce, turmeric, and adequate fiber are among the most well-researched dietary strategies for lowering hs-CRP. We also look at ultra-processed food intake, because even moderate consumption has been associated with measurably higher inflammatory markers. Gut testing can help rule out dysbiosis, infections and food sensitivities that may be contributing as well.
Important context: hs-CRP spikes acutely with any infection, injury, or illness, so we never interpret a single elevated value in isolation. Trend and clinical context matter.
5. Fasting Insulin Optimal range: 2–6 µIU/mL
Sarah Becker MS RD: This may be the single most underutilized lab in conventional medicine. Fasting blood glucose can remain perfectly "normal" for a decade while insulin climbs steadily, a sign the pancreas is working overtime to compensate for growing insulin resistance. By the time glucose is elevated, significant metabolic dysfunction has often been brewing for years. Fasting insulin catches the problem early.
Elevated fasting insulin is one of the most diet-responsive lab values we see in practice. Strategic carbohydrate timing, adequate protein at each meal, prioritizing fiber, and even meal sequencing (vegetables and protein before starches) can produce meaningful improvements in 8–12 weeks. This is an area where nutritional intervention often outperforms medication as a first-line approach.
6. Thyroid Panel (TSH + Free T3 + Free T4) Optimal range: TSH 1.0–2.0 mIU/L | Free T4 1.1–1.7 ng/dL | Free T3 3.2–4.4 pg/mL
Dr. Sinha: Most conventional thyroid testing stops at TSH alone, which tells us what the brain is asking the thyroid to do, but not whether the thyroid is actually delivering. TSH can look "normal" (within the wide conventional range of 0.5–4.5) while a patient is actively struggling with fatigue, weight gain, hair thinning, constipation, depression, cold intolerance, or slow recovery. We always want the full picture: TSH, Free T4 (the storage form of thyroid hormone), and Free T3 (the active form your cells actually use). The conversion from T4 to T3 is where many patients run into trouble. Conversion from T4 to T3 happens in the liver, kidney and intestine.
We also routinely add thyroid antibodies (TPO and anti-thyroglobulin) to screen for Hashimoto's, which is an autoimmune condition that frequently goes undetected for years. Treating the immune component, not just the hormone level, changes outcomes.
When you are pregnant, you get the benefit of a growing thyroid from your baby! Postpartum, you lose that extra thyroid gland and may feel the symptoms. Pregnancy also “suppresses” your immune system and you can get an autoimmune reaction to your own thyroid postpartum. Lots of important changes after pregnancy, so a great time to get your labs checked! (about 6-8 weeks after delivery or sooner if you notice unusual symptoms).
After having a baby, thyroid issues are common and if you had abnormal thyroid labs before pregnancy, it’s worth staying on top of in the postpartum period. Nutrition can play a big role. Foods rich in iodine (seaweed, fish), selenium (brazil nuts), zinc (pumpkin seeds) and iron (beef, poultry) are all beneficial for thyroid health and if you have thyroid antibodies, avoiding gluten can be helpful too.
How to Get These Labs
There are many other functional labs we like to see, and most of these can be ordered through your primary care provider. If your provider isn't familiar with functional ranges or declines to order the full panel, we can order them directly through your appointment with Dr. Sinha. Results are always reviewed in context alongside your symptoms, health history, and goals never as isolated numbers. From there, we can create a nutrition, lifestyle and supplement plan, personalized to you.
→ Book with Dr. Sinha for labs or a lab review
→ Book with Sarah for nutrition and supplement support
Warmly,
Dr. Sinha, MD Functional Medicine Physician
Sarah Becker, RD Registered Dietitian
This blog is for educational purposes only and does not constitute individualized medical advice. Please consult your provider before making changes to your supplementation or care plan.