Functional Testing: What’s Worth Measuring (and Why)

Key Points Summary

✓ Testing should inform action: Only order tests that will change what you do
✓ Hormone testing is tricky: Fluctuations make single tests less useful than patterns
✓ Nutrient status matters: Iron, ferritin, vitamin D, B12, and magnesium can all affect sleep
✓ Metabolic markers provide context: Blood sugar, inflammation, and thyroid function interact with sleep
✓ Comprehensive panels have limits: More testing isn’t always better

When I see a woman with perimenopausal sleep problems, part of my evaluation involves deciding what testing might actually help. This is a place where both conventional medicine and functional medicine can fall short in different ways—conventional medicine sometimes tests too little and misses contributing factors, while functional medicine sometimes tests too much and generates confusion without clarity.

The right approach is testing that will actually change what we do. I want to share how I think about this.

The Philosophy: Test to Inform Action

Every test I order, I ask myself: “If this comes back abnormal, what will I do differently? If it comes back normal, what does that tell me?”

If the answer to both questions is “nothing really,” I probably shouldn’t order it. Testing for the sake of being thorough, or to feel like we’re doing something, or because it’s part of a package, doesn’t serve you well. It generates information that doesn’t translate to better treatment.

With that philosophy in mind, here’s what I find genuinely useful.

Hormone Testing: More Complicated Than It Sounds

The first thing women often want is “hormone testing.” This seems reasonable—if perimenopause is about hormonal changes, shouldn’t we measure the hormones?

But it’s more complicated than it appears.

The fluctuation problem. During perimenopause, hormones fluctuate wildly—not just across the menstrual cycle but from day to day. A single blood draw captures one moment in a dynamic process. Your estradiol on Tuesday might be completely different from your estradiol on Friday.

What FSH tells us (and doesn’t). FSH (follicle-stimulating hormone) is often used to “diagnose” menopause. Elevated FSH suggests the ovaries are becoming less responsive. But FSH levels fluctuate too, and a “normal” FSH doesn’t rule out perimenopause. Conversely, an elevated FSH in a single sample doesn’t mean you’re definitively perimenopausal. It’s a clue, not a verdict.

The clinical picture matters more. Often, the pattern of your symptoms (cycle changes, hot flashes, sleep disruption, mood changes) tells us more about where you are in the menopausal transition than blood tests do.

When hormone testing adds value:

• If there’s uncertainty about whether you’re in perimenopause (particularly in younger women with symptoms)
• If evaluating for premature ovarian insufficiency
• As baseline before starting hormone therapy
• If considering testosterone therapy (testosterone levels are useful)
• Tracking AMH (anti-Müllerian hormone) for fertility planning

My approach: I don’t order hormone testing for every woman with perimenopausal sleep problems. When the clinical picture is clear, testing doesn’t change management. When there’s genuine uncertainty, it can help.

Nutrients That Matter for Sleep

Several nutrients directly affect sleep, and testing can identify deficiencies worth correcting.

Iron and ferritin. Low iron/ferritin is associated with restless legs syndrome, which disrupts sleep. This is common in women, especially those with heavy periods. I check ferritin (not just hemoglobin) because you can have low ferritin and still have normal hemoglobin. Ferritin below 50-75 ng/mL may contribute to restless legs, even though the “normal” range often goes lower.

Vitamin D. Low vitamin D is associated with poor sleep quality in observational studies. It’s easy to be deficient, especially if you don’t get much sun exposure. Checking 25-OH vitamin D and optimizing to 40-60 ng/mL is reasonable.

B12. Deficiency can cause neurological symptoms, fatigue, and mood changes that interact with sleep. Worth checking, especially if you feel tired or have brain fog, you’re vegetarian/vegan, take metformin, or are over 50.

Magnesium. Here’s a frustration: serum magnesium isn’t a good indicator of body stores. Most magnesium is inside cells, and blood levels are tightly regulated. You can be depleted and have normal serum magnesium. I often recommend magnesium supplementation empirically rather than relying on testing.

RBC magnesium (magnesium measured inside red blood cells) is somewhat better than serum but still imperfect. If available and not too expensive, it can be useful.

Thyroid Function: More Than TSH

Thyroid problems affect energy, mood, and sleep. They’re also more common in women and can emerge during the perimenopausal years.

Standard screening usually involves TSH (thyroid-stimulating hormone), which is a reasonable start. If TSH is abnormal, further testing (free T4, free T3, thyroid antibodies) is indicated.

But here’s where it gets nuanced: the “normal” range for TSH is quite wide, and some people don’t feel well at the higher end of normal. Functional medicine practitioners often aim for more optimal TSH (typically under 2.0 or 2.5), not just “normal.”

I think there’s something to this, though the evidence isn’t definitive. If someone’s TSH is technically normal at 4.0 but they have significant fatigue and other symptoms consistent with suboptimal thyroid, it’s worth having a conversation rather than reflexively saying “your thyroid is fine.”

Checking TPO antibodies (thyroid peroxidase antibodies) can identify Hashimoto’s thyroiditis, even when TSH is currently normal. This matters because it can predict future thyroid problems and sometimes explains symptoms even before frank hypothyroidism develops.

Metabolic Markers

Blood sugar regulation and metabolic health affect sleep, and testing can reveal issues worth addressing.

Fasting glucose and insulin. Glucose alone can be normal even when insulin resistance is developing. Fasting insulin adds information about how hard your body is working to maintain that glucose. High fasting insulin (even with normal glucose) suggests insulin resistance.

HbA1c. Reflects average blood sugar over the past 2-3 months. Levels 5.7-6.4 indicate prediabetes; 6.5+ indicates diabetes.

Lipid panel. Not directly about sleep, but relevant for overall cardiometabolic assessment, especially if considering hormone therapy.

hs-CRP. High-sensitivity C-reactive protein is a marker of inflammation. Chronic low-grade inflammation is associated with poorer sleep and can be elevated with obesity, metabolic syndrome, and other conditions.

These tests provide context for understanding whether metabolic factors might be contributing to sleep problems and inform lifestyle recommendations.

Cortisol and Adrenal Testing

Cortisol testing is popular in functional medicine, often framed around “adrenal fatigue” (a concept not recognized in conventional medicine).

Here’s my take: cortisol matters for sleep, and abnormal patterns can disrupt sleep. Cortisol should be high in the morning and low at night. If this rhythm is disrupted—high cortisol at night, for instance—it can cause trouble falling or staying asleep.

When cortisol testing might help:

• If there’s a clear stress-related pattern to sleep problems
• If symptoms suggest cortisol dysregulation (wired-but-tired at night, exhausted in the morning)
• As part of ruling out actual adrenal pathology (rare but real)

The testing options:

• Salivary cortisol (collected at multiple points across the day) can capture the rhythm
• Morning serum cortisol is a useful screen for actual adrenal insufficiency
• 24-hour urinary cortisol can assess total daily output

I don’t order cortisol testing on everyone. But when stress appears to be a significant driver and the clinical picture suggests cortisol dysregulation, it can inform treatment (though the interventions are often similar regardless: stress management, nervous system regulation, adaptogens).

Gut Testing: When It Makes Sense

The gut-brain axis is real, and gut issues can affect sleep and mood. But comprehensive gut testing (stool panels looking at microbiome composition, inflammation markers, digestive function) isn’t necessary for everyone.

When I consider gut testing:

• Significant GI symptoms (bloating, irregular bowel habits, discomfort)
• Strong suspicion of food sensitivities affecting symptoms
• Autoimmune conditions or systemic inflammation
• Treatment-resistant mood or sleep problems where we’ve addressed other factors

When it’s probably not necessary:

• GI function is fine
• Sleep problems have clear hormonal or stress-related drivers
• Simpler interventions haven’t been tried yet

Gut testing can be expensive and generate complex data. I use it selectively, not routinely.

What I Actually Order

For most women with perimenopausal sleep problems, my typical initial workup includes:

Standard labs:

• CBC (complete blood count)
• Complete metabolic panel
• TSH (thyroid)
• Fasting glucose and HbA1c
• Fasting insulin (if metabolic concerns)
• Iron, ferritin, TIBC
• Vitamin D
• B12

Added based on presentation:

• TPO antibodies (if thyroid symptoms)
• hs-CRP (if inflammatory or metabolic concerns)
• Hormone panel including FSH, estradiol (if diagnostic uncertainty)
• Lipid panel (if considering HT or assessing cardiovascular risk)
• RBC magnesium (if accessible and affordable)
• Cortisol assessment (if clear stress-related pattern)

Comprehensive functional panels:

• Reserved for more complex situations where simpler approaches haven’t worked
• Gut testing if GI symptoms or clinical indication
• More extensive nutrient testing if malabsorption is suspected

Using Results Wisely

Testing generates data. The question is what you do with it.

Low ferritin: Supplement iron, investigate if severe (heavy periods? bleeding?)

Low vitamin D: Supplement vitamin D

Suboptimal thyroid function: Trial of thyroid optimization, ongoing monitoring

Evidence of insulin resistance: Lifestyle intervention (nutrition, exercise), consider metabolic medications if significant

Elevated inflammation: Address drivers (weight, metabolic health, sleep itself, gut health)

Cortisol dysregulation: Stress management, adaptogens, nervous system work

The goal isn’t collecting data; it’s identifying actionable factors that inform treatment.

The Limits of Testing

I want to be honest about what testing can’t do.

It can’t measure your subjective experience. No test captures how miserable you feel at 3 a.m. when you’re lying awake for the fourth night in a row.

It can’t always explain symptoms. Sometimes everything tests “normal” and you still feel terrible. That doesn’t mean your symptoms aren’t real, it means our tests don’t capture everything relevant.

It doesn’t replace clinical judgment. The clinical picture—your history, your symptoms, your pattern—often matters more than lab values.

Testing is a tool. An important one, but just a tool. It’s most valuable when used thoughtfully to answer specific questions, not as a replacement for actually understanding what you’re experiencing.