5 Tests Worth Asking For at Your Next Appointment
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There are tests your doctor orders to rule out disease. And there are tests that tell you how well your body is actually functioning. Most standard panels only do the first one.
The reference ranges printed on your lab results were built by averaging a broad population — one that includes people who are sedentary, inflamed, and metabolically compromised. When your doctor tells you everything looks normal, what they're really saying is you fall somewhere in the middle of that group. That's not the same as thriving.
Here are five tests worth adding to the conversation at your next appointment — none of them exotic, all of them available at standard labs, and most of them rarely ordered.
Standard metabolic panels measure blood glucose — but glucose is a lagging indicator. By the time glucose becomes abnormal, insulin resistance has often been quietly progressing for years, or even decades.
Fasting insulin is measured separately and tells a fundamentally different story. You can have completely normal glucose while insulin is chronically elevated — a state called hyperinsulinemia that is now recognized as an early and independent marker of metabolic dysfunction.[1]
A 2023 paper published in Frontiers in Clinical Diabetes and Healthcare described hyperinsulinemia as "an early biomarker of metabolic dysfunction" — one that precedes abnormal glucose by years and is associated with cardiovascular disease, cognitive decline, and metabolic syndrome.[2] Despite this, fasting insulin is not part of routine screening for most women.
Functional target: Most functional medicine practitioners consider optimal fasting insulin to be below 8–10 μIU/mL. Standard lab ranges can run up to 25 μIU/mL — a threshold many metabolic health researchers consider far too permissive.
Hemoglobin tells you whether you're anemic. Ferritin tells you how much iron your body has in storage — and the gap between these two numbers is where most women fall through the cracks.
Hair follicle matrix cells are among the most rapidly dividing cells in the body and are extremely sensitive to even minor drops in iron availability. Research consistently shows women begin experiencing fatigue, hair loss, and brain fog at ferritin levels that most labs still consider normal.[3]
A 2023 study in PMC recommended redefining the normal ferritin threshold for women with hair loss at ≥60 ng/mL — substantially higher than the 12–15 ng/mL floor used by many standard labs.[4] A separate study found that the odds ratio for diffuse hair loss was 21.0 at ferritin levels ≤30 ng/mL.[5]
You can have completely normal hemoglobin and still have insufficient iron stores for optimal hair growth, energy, and recovery. The standard lower limit at some labs is 12. The functional target for hair health alone is 50 to 70.
Synthesis of clinical research — PMC 2023, PubMed 2010TSH — thyroid stimulating hormone — is the standard thyroid marker ordered on most panels. But TSH measures a signal from the brain, not what's happening at the cellular level. Free T3 is the active form of thyroid hormone that actually enters your cells and drives metabolism.
It's entirely possible to have a normal TSH while conversion from T4 to the active Free T3 is impaired — a pattern that can produce classic hypothyroid symptoms including fatigue, weight gain, cold intolerance, and brain fog despite a "normal" thyroid panel.
These are not the same number. And only one of them explains how you feel.
Vitamin D deficiency is widespread, and the gap between what labs call "sufficient" and what researchers consider optimal is significant. The standard reference range marks 30 ng/mL as sufficient — but functional medicine targets are typically 60 to 80 ng/mL, a level associated with better immune function, mood regulation, hormone balance, and metabolic health.
When ordering, specify 25-OH D3 — the specific form that reflects your body's true vitamin D status. Some panels default to a combined D2/D3 measure that can obscure deficiency.
CRP is a protein produced by the liver in response to inflammation. The high-sensitivity version (hs-CRP) can detect low-grade, chronic inflammation that standard CRP tests miss — the kind of slow-burn inflammatory state that drives cardiovascular disease, metabolic dysfunction, and accelerated aging years before symptoms appear.
Many standard panels include a basic CRP, but the high-sensitivity version is what you want. It's the difference between a smoke alarm that only triggers in a fire and one that detects a smoldering ember.
Optimal target: Below 1.0 mg/L. Above 3.0 mg/L is considered high risk for cardiovascular events. Most labs only flag results above 10 mg/L — far above where the damage is already accumulating.
The Summary
None of these tests are obscure, experimental, or difficult to access. All five are available through standard labs. Most of them can be added to an existing blood draw with a simple conversation with your provider — or ordered directly through functional medicine practices or lab ordering services.
The goal of standard screening is to catch disease. The goal of optimization is to prevent it. These five tests are the difference between the two. Understanding your own biomarkers — knowing what the numbers mean, what optimal looks like, and what questions to ask — is one of the most powerful things you can do for your long-term health.
References
- 1Sung KC et al. Elevated fasting insulin predicts the future incidence of metabolic syndrome: a 5-year follow-up study. Cardiovascular Diabetology. 2011;10:108. doi:10.1186/1475-2840-10-108
- 2Vaidya RA et al. Hyperinsulinemia: an early biomarker of metabolic dysfunction. Frontiers in Clinical Diabetes and Healthcare. 2023;4:1159664. doi:10.3389/fcdhc.2023.1159664
- 3Serum ferritin and vitamin D levels should be evaluated in patients with diffuse hair loss prior to treatment. PMC. 2020. PMC7394174
- 4Diagnosis and treatment of female alopecia: Focusing on the iron deficiency-related alopecia. PMC. 2023. Recommends redefining normal ferritin as ≥60 ng/mL. PMC10683524
- 5Rushton DH. Iron status in diffuse telogen hair loss among women. PubMed. 2009. Odds ratio 21.0 for hair loss at ferritin ≤30 ng/mL. PMID:20021982
- 6Zhang X et al. Fasting insulin, insulin resistance, and risk of cardiovascular or all-cause mortality in non-diabetic adults: a meta-analysis. Bioscience Reports. 2017;37(5). doi:10.1042/BSR20170947
- 7Levels Health. What are normal levels of insulin and why don't we test it more? Summary of functional medicine expert recommendations. levels.com