Written by Dr. Ryan Kneessi, ND · Last updated November 5, 2026

Lab reports can list dozens of markers, and each one is a small window into how a different system in the body is working. This page gathers my plain-language guides to common functional lab markers in one place and groups them by body system, so you can find the marker you are curious about and read what it measures, what higher or lower results generally reflect, and how researchers connect it to the deeper mechanisms of aging and root causes.

Every guide is educational and cites the published research it draws on. A single result is best read in context, alongside your history, other markers and the direction your numbers move over time, and your own provider is the right person to help you interpret it. You can also see the specialty tests I commonly recommend on my functional labs page.

Metabolic health

Adiponectin: Explains what adiponectin, a hormone made by fat tissue, reflects about insulin sensitivity and inflammation, and why very high levels can mean something different in older adults.
Fasting Insulin and HOMA-IR: Explains what fasting insulin and HOMA-IR suggest about how hard the body works to keep blood sugar steady.
Glucose Variability and Fructosamine: Explains what fructosamine, a two-to-three-week blood sugar average, and swings in fasting or day-to-day glucose reflect beyond a single glucose or HbA1c number.
Glycemic Control: Looks at blood sugar and insulin markers and how glycemic control relates to aging.
HbA1c (Hemoglobin A1c): Explains what HbA1c shows about average blood sugar over about three months and what can skew the result.
Inositol Levels: Explains what measured myo-inositol and D-chiro-inositol levels reflect about insulin signaling, and why the evidence for inositol as a lab marker is still limited.
Leptin, IGF-1 and Uric Acid: Explains what leptin
Triglyceride-to-HDL Ratio: Explains what the triglyceride-to-HDL ratio from a standard lipid panel reflects about insulin sensitivity and the type of LDL particles in the blood.

Heart and blood vessels

ADMA and SDMA: Explains how ADMA and SDMA relate to nitric oxide and blood vessel function.
ApoB Test: Explains why ApoB counts the particles that carry cholesterol.
Arginine and the Arginine-to-ADMA Ratio: Explains what blood arginine, the arginine-to-ADMA ratio and the global arginine bioavailability ratio reflect about how much raw material blood vessels have for making nitric oxide.
Ceramides Blood Test: Describes ceramides as signaling fats and what research says about them and heart health.
Fibrinogen: Explains what fibrinogen, a liver-made clotting protein that also rises with inflammation, reflects when it shows up on a cardiovascular panel.
Heart Strain Markers: Covers NT-proBNP and other markers that reflect strain on the heart.
Lipoprotein(a): Describes lipoprotein(a) as an inherited heart marker that is usually measured once.
Omega-6 to Omega-3 Ratio and Arachidonic Acid: Explains what the omega-6 to omega-3 and AA-to-EPA ratios reflect, why low omega-3 usually drives a high ratio, and what research shows about linoleic and arachidonic acid.
Plant Sterols in the Blood: Explains what blood levels of plant sterols such as sitosterol and campesterol reflect about how much cholesterol the gut absorbs versus how much the body makes.
Small Dense LDL (sdLDL): Explains why the size of LDL particles may matter alongside the standard cholesterol number.
The Omega-3 Index: Explains what the Omega-3 Index measures and what studies have found.
Understanding Your Cholesterol Panel: Walks through the standard cholesterol panel and newer lipid markers.
VO2 Max and Longevity: Explains why cardiorespiratory fitness is studied as a marker of healthy aging.

Inflammation

IL-6 (Interleukin-6): Explains IL-6 as an inflammatory messenger that tends to rise with age.
Inflammation Blood Tests: Covers hs-CRP
MMP-9: Explains what matrix metalloproteinase 9, an enzyme that reshapes the scaffolding between cells, reflects when it is measured in stool or blood.
Neutrophil-to-Lymphocyte Ratio: Explains what the neutrophil-to-lymphocyte ratio from a routine blood count reflects about the balance between inflammatory activity and adaptive immunity.
TNF-Alpha: Explains what tumor necrosis factor alpha, a messenger that helps start the inflammatory response, reflects and how persistently higher levels relate to aging.
hs-CRP Test: Explains what the hs-CRP test reflects about whole-body inflammation.

Nutrients and minerals

Amino Acid Profile: Explains what a plasma amino acid profile shows about protein intake and metabolism, and why higher branched-chain amino acids are studied as an early metabolic signal.
Choline Levels: Explains what choline does for cell membranes, the liver, methylation and the brain, and why a blood level does not tell the whole story.
Chromium Levels: Explains what chromium measurements in blood, urine or toenails can and cannot say about status, and what research links chromium to blood sugar and heart health.
Copper and Ceruloplasmin Levels: Explains what serum copper and ceruloplasmin reflect, why both rise with inflammation, and what research links higher levels to heart and brain health.
Ferritin Levels Explained: Explains what low or high ferritin reflects about iron stores.
Folate Blood Test: Explains what a folate blood test shows about this nutrient for cell growth and repair.
RBC Magnesium: Explains why serum magnesium can look normal when total magnesium is low and what a red blood cell magnesium test adds.
Selenium Levels: Explains how selenium supports thyroid hormones and antioxidant enzymes and why both low and high levels matter.
Serum Iron Test: Explains what a serum iron result can and cannot show.
TIBC Blood Test: Explains total iron-binding capacity and how it fits an iron panel.
Thiamine (Vitamin B1) Levels: Explains what thiamine (vitamin B1) tests reflect about the nutrient cells need to turn glucose into energy, and why levels can run low in diabetes and heart failure.
Transferrin Blood Test: Describes transferrin as the protein that carries iron in the blood.
Transferrin Saturation: Explains what transferrin saturation says about how iron is being used.
UIBC Blood Test: Explains unsaturated iron-binding capacity and how it fits an iron panel.
Vitamin A (Retinol) Levels: Explains what a serum retinol test reflects about vitamin A status, why it stays steady until liver stores run low, and what research links low and very high levels to.
Vitamin B12 Blood Test: Explains what a vitamin B12 blood test shows and common reasons it runs low.
Vitamin B6 (PLP) Levels: Explains what a plasma pyridoxal 5-phosphate (PLP) test reflects about vitamin B6 status, why levels tend to run lower with inflammation, and what population research links them to.
Vitamin C Levels: Explains what a plasma or serum vitamin C test reflects about recent intake, why smokers tend to run lower, and how levels relate to long-term health in population studies.
Vitamin D Blood Test (25-OH): Explains the 25-OH vitamin D test and what low levels can reflect.
Vitamin E (Tocopherol) Levels: Explains what a serum alpha-tocopherol test reflects about vitamin E status, why it is best read alongside blood fats, and what long-term research links higher and lower levels to.
Vitamin K2 Status: Explains how vitamin K status is measured, why K2 is hard to see in blood, and how it connects to calcium in bones and arteries.
Who Should Consider Iron (and Who Should Not)? Ferritin Guide: Explains who may need iron and why ferritin is checked first.
Zinc-to-Copper Ratio: Explains how the balance between zinc and copper relates to inflammation.

Hormones

Androstenedione Levels: Explains androstenedione as the precursor hormone that becomes testosterone and estrone, and what research links higher levels to in women and men.
Cortisol Blood Test: Explains what high or low cortisol on a blood test can reflect.
Cortisol Patterns: Explains why cortisol patterns through the day can tell more than one blood draw.
Cortisol to Cortisone Ratio: Explains what the balance between active cortisol and inactive cortisone in urine reflects about how the body switches its main stress hormone on and off.
DHEA-S Blood Test: Explains what a DHEA-S level reflects about adrenal hormone output.
Estradiol Blood Test: Explains what high or low estradiol levels can reflect.
Estriol (E3) Levels: Explains estriol as the weakest of the three main estrogens, what a result reflects about estrogen metabolism, and what research shows about it.
Estrogen Dominance: Explains estrogen dominance and estrogen metabolism when standard labs look normal.
FSH Blood Test: Explains what FSH shows about reproductive hormone signaling.
Free Testosterone Test: Explains when free testosterone can say more than total testosterone.
LH Blood Test: Explains what luteinizing hormone shows about reproductive hormone signaling.
Perimenopause or PCOS? Symptoms, Hormone Testing, and Support: Compares perimenopause and PCOS patterns and the hormone tests used to explore them.
Pregnenolone Test: Describes pregnenolone as an early building block for other hormones.
Progesterone Blood Test: Explains what a progesterone blood test shows.
Progesterone Metabolites: Explains what urinary pregnanediol and the brain-active metabolite allopregnanolone reveal about how the body produces and uses progesterone.
Prolactin Blood Test: Explains what a high prolactin result can reflect.
SHBG Blood Test: Explains how SHBG affects the amount of active sex hormones.
Total Testosterone Test: Explains total testosterone and what low levels can look like in men and women.

Thyroid

Free T3 Test: Explains free T3 as the active thyroid hormone available to cells.
Free T4 Test: Explains free T4 as the thyroid's circulating reservoir hormone.
Reverse T3: Explains what reverse T3 can and cannot tell you.
T3 Blood Test: Explains what a T3 result shows about the active thyroid hormone.
T4 Blood Test (Thyroxine): Explains what a total T4 result means.
TPO Antibodies Test: Explains TPO antibodies as an early autoimmune thyroid marker.
TSH Test: Explains what TSH shows about the signal that drives the thyroid.
Thyroglobulin Antibodies Test: Explains thyroglobulin antibodies as an autoimmune thyroid marker.

Gut health

Akkermansia on a Stool Test: Explains what the amount of Akkermansia muciniphila in a stool sample reflects about the gut mucus layer and why more is not automatically better.
Beta-Glucuronidase: Explains how the gut enzyme beta-glucuronidase can reactivate estrogens and other compounds the liver has packaged for removal.
Calprotectin: Explains what stool calprotectin reflects about inflammation in the gut lining and which everyday factors can raise it.
Eosinophil Protein X: Explains what eosinophil protein X in stool reflects about the activity of eosinophils, white blood cells in the gut lining tied to allergic responses and defense against parasites.
Faecalibacterium prausnitzii: Explains Faecalibacterium prausnitzii, one of the main butyrate-producing gut bacteria, what a lower stool result reflects and what research links it to.
Fecal Bile Acids: Explains what fecal bile acids show about bile reaching the colon and how gut bacteria reshape it, and what research links higher levels to.
Lactoferrin: Explains what fecal lactoferrin reflects about white blood cell activity in the gut lining and how it compares with calprotectin.
S100A12: Explains what S100A12, an alarm protein released by activated neutrophils, reflects about inflammation in the gut lining and how it compares with calprotectin.
Secretory IgA: Explains what secretory IgA does as the gut lining's first line of immune defense and why a stool result is read in context.
Stool pH: Explains what stool pH shows about fermentation by gut bacteria, why it shifts with diet and transit, and what research links it to the microbiome.
Testing for Leaky Gut: Looks at the options and limits of testing for intestinal permeability.

Everyday exposures

Heavy Metals: Covers common sources of heavy metals and how testing works.
Urine Arsenic: Explains what a urine arsenic test shows about recent exposure from water, food and other sources, and what research links higher inorganic arsenic to.
Urine Atrazine: Explains what a urine atrazine or atrazine mercapturate result shows about recent herbicide exposure, and what human research links higher exposure to.
Urine Cadmium: Explains what a urine cadmium result reflects about longer-term body burden from smoking and food, and what research links higher levels to bone and kidney findings.
Urine Parabens: Explains what a urine paraben test shows about recent exposure to common cosmetic and product preservatives, and what research links higher levels to.

Cellular energy and mitochondria

8-OHdG: Explains 8-OHdG as a urine marker of oxidative damage to DNA.
Advanced Glycation End Products (AGEs): Explains how sugar binding to proteins and fats forms AGEs and why researchers study them in aging.
CoQ10 Levels: Explains CoQ10 as a mitochondrial energy compound and what low levels can reflect.
Krebs Cycle Markers (Organic Acids): Explains what Krebs cycle organic acids such as citrate and succinate reflect about how cells make energy.
Malondialdehyde (MDA): Explains MDA as a marker of oxidative damage to fats and why the way it is measured matters.

Brain health

GFAP and S100B: Explains what blood levels of GFAP and S100B, two proteins from the brain's support cells, can reflect about brain strain, injury and early changes with age.

Kidney and liver

CK, LDH and GGT Blood Tests: Explains what elevated CK
IgG, IgM and Cystatin C: Covers total IgG

Bone and muscle

DPD and PYD: Explains how the collagen crosslinks deoxypyridinoline and pyridinoline in urine reflect the rate at which bone is being broken down.
Grip Strength as a Longevity Biomarker: Explains why grip strength is studied as a marker of healthy aging.
Parathyroid Hormone (PTH) Test: Explains how parathyroid hormone regulates calcium and bone.

Immune and autoimmune

ANA Test: Explains what antinuclear antibodies are, why a positive ANA is common in healthy people, and how titer and pattern shape what the result reflects.
Anti-CCP Antibody Test: Explains the anti-CCP antibody test and what a positive result can mean.
Rheumatoid Factor (RF) Test: Explains what a positive rheumatoid factor result can mean.

This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before making changes to your diet, exercise, supplements, or medications, especially if you are pregnant, nursing, or managing a health condition.