This question is highly personal and depends on several factors, but after observing lab trends for the past 10 years, I consistently see many of the same common blood markers overlooked or dismissed as “normal.” I am also alarmed at how rarely nutritional inadequacies are ruled out as contributors to various diagnoses or symptoms.

Because of this, I strongly encourage my clients to advocate for several lab markers that are inexpensive and yet invaluable for understanding possible root causes of symptoms. I cannot recommend these as medical interventions, of course, but from an educational standpoint, I hope you find this informative and actionable at your next well check.

One of the top questions I get from clients is, “What labs should I ask my PCP to run?”

Vitamin D

• Traditional medicine typically recommends: Testing only if deficiency is suspected; sufficiency often defined as ≥30.
• What I recommend: Routine testing at least annually, with an optimal target range of 45–80.
• Why it’s crucial: Immune function, inflammation regulation, bone health, and overall disease risk.

My #1 top recommendation, if you haven’t done it in the past year, is to have your Vitamin D levels checked. It is inexpensive to test, it is a common deficiency that affects essentially all organs in the body and many disease states, and most providers will agree to add it to a standard well-check panel. (Note: Vitamin D is NOT included with standard labs, believe it or not.) You do have to ask for it, but most providers will oblige because it is so well substantiated in the research literature.

Most lab ranges are around 30–100, but as a functional medicine dietitian, I would argue that a level between 45 and 80 is most beneficial. There are at least 50 studies in the past five years (if there’s one good thing that came out of COVID, it’s this!) supporting less hospitalization and reduced severity of viral illness when blood levels of Vitamin D are at least 45. In cases of autoimmune disease and cancer, blood levels of 70–80 may be additionally protective. There is minimal research related to Vitamin D levels greater than 100, so I typically recommend avoiding that range, as studies are mixed on whether it is protective or possibly harmful.

Once you’ve had Vitamin D tested, remember your level or save it somewhere for future reference. If deficient, it may take three or more months to increase to a more optimal level, so it’s helpful to track what supplement dosage gets you there. I typically recommend 5,000 IU per day for three months, then re-check to see how much levels have increased. From there, adjust as needed to maintain. Another re-check may be required to confirm what that amount is, as it may be less than the 5,000 IU per day required to increase blood levels.

The exact amount of Vitamin D needed to maintain a blood level of at least 45 will vary from person to person. Genetics (such as the VDR gene) play a role, as well as skin color and active disease states such as obesity or diabetes, which may require a higher ongoing dose to support adequate levels. Personally, I have seen among my clients that somewhere between 2,000–5,000 IU per day for maintenance is usually optimal.

Anyone can benefit from measuring Vitamin D levels, but especially those with an autoimmune history or tendencies, frequent colds or illness, or those dealing with a chronic condition such as cancer, diabetes, obesity, or thyroid conditions. It is such a simple tool to support the immune system gently and naturally, with well-documented benefits.

Insulin

• Traditional medicine typically recommends: Fasting glucose and/or Hemoglobin A1C to assess blood sugar control.
• What I recommend: Adding fasting insulin to catch early insulin resistance before glucose markers become abnormal.
• Why it’s crucial: Blood sugar regulation, metabolic health, weight balance, and hormone signaling.

Insulin is not a commonly checked blood marker, but it can be immensely helpful beyond the standard fasting glucose included in a Comprehensive Metabolic Panel (CMP), which is typically tested annually. Some providers also check Hemoglobin A1C, which is a three-month average of blood glucose levels. This can be helpful to observe trends beyond a single measurement, such as fasting glucose.

However, I have seen blood sugar instability—meaning large fluctuations within a day—in clients who still have a “normal” A1C. In other words, even if blood sugar swings up and down like a rollercoaster, the average may still appear normal. A fasting insulin level provides an additional clue as to how the body is handling carbohydrates from a proactive perspective rather than a reactive one.

This marker is most helpful when done fasting, with a lower level (4–6) being ideal. This suggests that, at rest, the body is not producing excessive amounts of insulin. If fasting insulin levels are higher (above 8–10), this may imply an early stage of insulin resistance, where the body produces more insulin due to decreased sensitivity to its effects on blood glucose. While this is not diagnostic on its own, it can provide valuable insight into potential root causes of weight gain or hormonal imbalances that further testing may help clarify.

Thyroid Panel

• Traditional medicine typically recommends: TSH alone as an initial thyroid screening tool.
• What I recommend: A full thyroid panel including TSH, Free T4, Free T3, thyroid antibodies, and sometimes Reverse T3.
• Why it’s crucial: Metabolism, energy production, digestion, temperature regulation, and cognitive function.

Many clients tell me early on that they feel hopeless when they’re struggling with symptoms such as constipation, weight gain, fatigue, brain fog, dry skin, or thinning hair, because their “doctor said my thyroid is normal.” First of all—what does that even mean? What blood markers define a normally functioning thyroid? And is there a difference between normal and optimal?

This topic is near and dear to my heart because I, too, struggled for years trying to understand normal versus optimal, what to ask for, and what the standard of care dictates in traditional doctor’s offices.

The standard screening marker for thyroid function is TSH. That’s it—one number. And it’s not even a thyroid hormone. It’s a pituitary hormone that reflects what the thyroid is producing. I meet many women who may be dealing with “sub-clinical” hypothyroidism, meaning they are symptomatic but their blood levels appear within range, especially if only one marker is checked.

For this reason, a full thyroid panel should include additional values such as Free T4, Free T3, thyroid antibodies (especially if there is any positive family history of thyroid disease), and sometimes Reverse T3, which can be helpful for those on T3 medication or with suspected cortisol imbalance.

Free T4 is essentially the raw material produced from the nutrients we consume. However, it must be converted in order to be used. This raises two important questions: is the issue too little T4 production, or poor conversion? To answer that, we must also test Free T3, the most bioactive form of thyroid hormone that influences metabolism and other downstream processes.

Free T3 is the star of the show. It is the most bioactive form of thyroid hormone and plays a key role in metabolic function. Slightly or moderately low Free T3 levels (2–2.7) are fairly common in the client population I see—primarily women ages 35–55. In many cases, diet changes and/or supplements can gently support levels closer to 3–3.5, often resulting in meaningful symptom improvement. It can truly be a game-changer, but we have to test to know.

Reverse T3 is a more obscure blood marker, and many providers don’t routinely check it. In situations where hypothyroid symptoms are present but TSH remains in range, Reverse T3 can be helpful in understanding the root cause of dysfunction. It acts as a sort of “exit pathway” for excess T3 that the body does not want to use.

This pattern is most common during chronic stress, when the body essentially downshifts metabolism to prevent further strain. In these cases, thyroid dysfunction may not originate in the thyroid itself at all. Instead, cortisol imbalance or cellular inefficiencies may be the underlying issue, which completely changes how we approach hypothyroid symptoms with “normal labs.”

Other Helpful Nutritional Labs

• Traditional medicine typically recommends: Screening for anemia or deficiency only when values fall outside standard reference ranges.
• What I recommend: Evaluating ferritin and B12 through an optimal (not just normal) lens, especially in symptomatic individuals.
• Why they’re crucial: Oxygen delivery, neurological health, energy production, sleep quality, and cognitive performance.

Ferritin is a form of stored iron and is an earlier nutritional indicator of iron deficiency than hemoglobin levels. It is inexpensive to order and can often be added to a CBC, which is a standard annual well-check lab. From a nutritional standpoint, I do not agree that a range of 20–150 is sufficient to define optimal levels. This is another example of how “normal” does not always equate to optimal.

In my one-on-one clinical experience, ferritin levels between 50–90 are more optimal, especially for active, menstruating women and for children. I frequently see young women told their ferritin of 20–30 is normal, yet they struggle with symptoms of iron deficiency such as fatigue, dizziness, brain fog, and poor sleep. It is also important to note that ferritin levels closer to the upper end of the range may indicate iron overload or chronic inflammation and may warrant additional testing.

B12 is another common deficiency worth checking in those dealing with fatigue, shortness of breath, depression, or poor memory. Similar to ferritin, traditional lab ranges are broad because they are based on population averages rather than optimal health. Most of my clients feel best with a B12 level between 600–900, even though levels above 200–300 are typically considered normal.

There are also nuances with B12 testing. In some cases, serum levels may appear normal while red blood cell (RBC) levels remain low, which requires deeper interpretation. This is particularly relevant for individuals consuming B12-fortified foods. The B12 added to energy drinks, protein shakes, and cereals is often a poorly absorbed form that can raise serum levels without effectively supporting cellular metabolism.

In my experience, most people respond well to methyl-B12. If symptoms persist despite improved blood levels, I often suggest hydroxo- or adenosyl-B12 forms.

Lab Testing FAQs

Do I need all of these labs every year?
Not necessarily. Some labs are helpful annually, while others may only need to be checked if symptoms are present or if you’re monitoring a known imbalance.

Will my primary care provider order these labs?
Many providers will order them if you ask, especially when framed as preventative or symptom-driven. Some markers may require advocacy or follow-up discussion.

Are these labs covered by insurance?
Coverage varies by plan. Many of these labs are relatively inexpensive, even when paying out of pocket.

What if my labs are “normal” but I still feel unwell?
This is where the difference between normal and optimal matters. Labs can fall within reference ranges while still contributing to symptoms.

Can I interpret these labs on my own?
While lab results are accessible, proper interpretation requires context. Trends, symptoms, and lifestyle factors all matter.

Is this medical advice?
No. This information is for educational purposes only and is meant to support informed conversations with your healthcare provider.

What other labs do you have questions about? Have you had any of the above tested and been surprised by the results? Next month, I’ll be reviewing essential hormone labs—so stay tuned!

Want help interpreting your labs or knowing what to ask for?