Health Metrics Encyclopedia
Every biometric, cycle signal, hormone, and symptom Go Go Gaia tracks, defined in one place and sourced to real research. Each entry explains what a metric measures and how it's measured, not what your own number means.
Educational reference content, not medical advice. Entries describe what the research shows at a population level. For questions about your own results, please consult your doctor.
Biometrics & Vitals
- HRV (Heart Rate Variability) The variation in time between heartbeats, tracked overnight as a signal of autonomic nervous system balance.
- Resting Heart Rate Beats per minute at rest, typically measured overnight or first thing in the morning.
- Basal Body Temperature Body temperature at rest, taken immediately on waking, used to spot the post-ovulation temperature shift.
- HRV: RMSSD The specific HRV calculation most consumer wearables report.
- Heart Rate Beats per minute, measured continuously or on demand.
- Wrist Temperature Skin temperature sampled at the wrist overnight by devices like Apple Watch.
- Blood Pressure The force of blood against artery walls, recorded as systolic over diastolic.
- Respiratory Rate Breaths per minute at rest, tracked overnight by many wearables.
- SpO2 (Blood Oxygen Saturation) The percentage of oxygen-saturated hemoglobin in the blood.
- VO2 Max An estimate of the maximum rate of oxygen your body can use during exercise.
- Blood Glucose The concentration of sugar in the blood, measured via fingerstick or continuous glucose monitor.
- Sleep Stages REM, deep, and core sleep as estimated by wearable sensors overnight.
- Sleep Latency How long it takes to fall asleep after getting into bed.
- Body Temperature Core body temperature, distinct from basal or skin temperature readings.
- Active Energy Calories burned through movement above resting baseline.
- Step Count Steps taken per day, counted by an accelerometer in a phone, watch, or fitness tracker.
Cycle & Fertility
- Cervical Mucus Vaginal discharge that changes texture across the cycle and is used as a fertility-awareness sign.
- LH Surge The rapid rise in luteinizing hormone that triggers ovulation.
- Luteal Phase The second half of the cycle, from ovulation to the next period.
- Follicular Phase The first half of the cycle, from the start of the period to ovulation.
- Cervical Position Changes in cervix height, softness, and openness across the cycle.
- Ovulation Test (OPK) A urine test strip that detects the LH surge ahead of ovulation.
- Period Flow The volume and pattern of menstrual bleeding, typically logged by intensity.
- Ovulation The release of an egg from the ovary, roughly midway through a typical cycle.
- Menstrual Phase The days of active bleeding at the start of the cycle.
- Fertile Window The days in a cycle when pregnancy is biologically possible.
- Cycle Length The number of days from the first day of one period to the first day of the next.
- Spotting / Intermenstrual Bleeding Light bleeding that occurs outside the expected period.
- Anovulatory Cycle A cycle in which no egg is released.
Hormones & Labs
- AMH (Anti-Müllerian Hormone) A hormone produced by ovarian follicles, commonly used as a marker of ovarian reserve.
- Estradiol The primary form of estrogen during reproductive years, rising and falling across the cycle.
- TSH (Thyroid-Stimulating Hormone) A pituitary hormone that signals the thyroid gland to produce thyroid hormone.
- Ferritin A protein that stores iron, used as a lab marker of the body's iron reserves.
- Estrone (E1) A weaker form of estrogen, more prominent after menopause.
- Progesterone The hormone that rises after ovulation and supports the luteal phase.
- FSH (Follicle-Stimulating Hormone) The pituitary hormone that stimulates follicle growth in the ovary.
- Testosterone An androgen hormone present in smaller amounts in women, involved in libido and muscle maintenance.
- Free Testosterone The portion of testosterone not bound to carrier proteins, considered biologically active.
- SHBG (Sex Hormone-Binding Globulin) A protein that binds sex hormones in the blood, affecting how much is free and active.
- DHEA-S An adrenal androgen used as a marker of adrenal hormone production.
- Prolactin A pituitary hormone best known for its role in milk production.
- Cortisol The primary stress hormone, produced by the adrenal glands on a daily rhythm.
- Insulin The hormone that regulates blood sugar by moving glucose into cells.
- Free T4 (Free Thyroxine) The unbound, biologically active portion of thyroxine, the thyroid gland's main secreted hormone.
- Free T3 (Free Triiodothyronine) The small unbound fraction of T3, the biologically active thyroid hormone, circulating in blood.
- Reverse T3 (rT3) An inactive form of thyroid hormone produced when deiodinase enzymes break down T4.
- Thyroid Antibodies (TPO & Thyroglobulin Antibodies) Immune proteins that target parts of the thyroid gland, used as markers of thyroid autoimmunity.
- hCG (Human Chorionic Gonadotropin) A hormone made by the developing placenta and detected by pregnancy tests.
- PdG (Pregnanediol Glucuronide) The urinary metabolite of progesterone, used to confirm ovulation without a blood draw.
- E3G (Estrone-3-Glucuronide) A urinary breakdown product of estradiol, read by at-home fertility monitors to track the estrogen curve.
- 17-OH Progesterone (17-Hydroxyprogesterone) A steroid hormone made as an in-between step on the pathway from progesterone toward cortisol.
- Androstenedione An androgen produced by the ovaries and adrenal glands that serves as a precursor to testosterone and estrone.
- Urinalysis The standard urine test, done three ways: a visual color check, a chemical dipstick, and a microscope exam.
- Urine Hormone Metabolites Urinary cortisol, melatonin's breakdown product aMT6s, and the DNA-oxidation marker 8-OHdG.
Metabolic, Kidney & Liver Labs
- Fasting Glucose Blood glucose measured after at least eight hours without food, a baseline reading on standard metabolic panels.
- HbA1c (Hemoglobin A1c) The share of hemoglobin with glucose attached, reflecting average blood glucose over roughly three months.
- C-Peptide A protein chain the pancreas releases alongside insulin in equal amounts, measured by lab blood draw.
- Creatinine A muscle waste product filtered by the kidneys, a standard part of routine bloodwork and kidney function estimates.
- BUN (Blood Urea Nitrogen) The amount of urea nitrogen in the blood, a liver-made waste product filtered out by the kidneys.
- eGFR (Estimated Glomerular Filtration Rate) A calculated estimate of how fast the kidneys filter blood, derived from creatinine plus age and sex.
- ALT (Alanine Aminotransferase) A liver enzyme that leaks into the blood when liver cells are stressed or damaged.
- AST (Aspartate Aminotransferase) An enzyme found in the liver, heart, muscle, kidneys, and red blood cells, released when those cells are damaged.
- Alkaline Phosphatase (ALP) An enzyme made mainly in the liver and bone, measured as part of a liver or metabolic panel.
- Bilirubin (Total & Direct) A pigment made when the body breaks down heme from retired red blood cells, reported as total and direct fractions.
Lipids & Heart Health Labs
- Total Cholesterol The combined amount of cholesterol in the blood, counting the cholesterol carried by every type of lipoprotein particle, including HDL, LDL, and VLDL.
- HDL Cholesterol The cholesterol carried inside high-density lipoprotein particles, the smallest and densest of the lipoprotein particles that move fats through the bloodstream.
- LDL Cholesterol The cholesterol carried by low-density lipoprotein, the particle that delivers most of the cholesterol circulating in blood to tissues around the body.
- Triglycerides A fat molecule built from one glycerol backbone joined to three fatty acids, the body's main form of stored and transported fat.
- ApoB (Apolipoprotein B) The main structural protein of LDL, VLDL, and related lipoprotein particles, with one ApoB molecule on each particle.
- Lipoprotein(a) A cholesterol-carrying particle built like an LDL particle with an extra protein, apolipoprotein(a), bonded to its surface.
Blood Count (CBC)
- Hemoglobin The iron-containing protein inside red blood cells that picks up oxygen in the lungs and carries it to the rest of the body.
- Hematocrit The fraction of blood volume taken up by red blood cells, reported as a percentage.
- Red Blood Cell (RBC) Count The number of red blood cells, the body's oxygen-carrying cells, in a set volume of blood.
- White Blood Cell (WBC) Count The number of white blood cells, the cells of the immune system, in a set volume of blood.
- Platelet Count The number of platelets, the small cell fragments that clump to stop bleeding, in a set volume of blood.
- MCV (Mean Corpuscular Volume) The average size of red blood cells, one of the red cell indices reported as part of a complete blood count.
Iron, Inflammation & Nutrients
- Serum Iron The iron circulating in blood, bound to the carrier protein transferrin, measured by blood draw.
- TIBC & Transferrin Saturation How much iron the blood's transferrin can carry (TIBC) and the share of that capacity currently in use.
- hs-CRP (High-Sensitivity C-Reactive Protein) A high-sensitivity blood test for C-reactive protein, a liver-made marker of inflammation.
- ESR (Erythrocyte Sedimentation Rate) How far red blood cells settle in a tube of blood over one hour, an older marker of inflammation.
- Homocysteine An amino acid produced during methionine metabolism, kept in check by B12, folate, and B6.
- Vitamin D (25-Hydroxyvitamin D) The standard blood test for vitamin D status, measuring the storage form circulating in blood.
- Vitamin B12 A cobalt-containing vitamin the body needs for DNA synthesis and red blood cell formation.
- Folate (Vitamin B9) The B vitamin behind DNA synthesis and new cell formation.
- Vitamin A (Retinol) A fat-soluble vitamin measured on lab panels as serum retinol.
- Zinc An essential trace mineral behind hundreds of enzymes, with no dedicated body store.
Symptoms
- Hot Flashes A sudden wave of heat across the face, neck, and chest, often with sweating, most common during the menopause transition.
- Night Sweats Episodes of heavy sweating during sleep, sharing the same physiology as hot flashes.
- Hirsutism Coarse, pigmented hair growth in areas where growth depends on androgens, such as the face and chest.
- Hormonal Acne Acne that tracks with hormone shifts, driven by androgen receptors in sebaceous glands.
- Hair Thinning A drop in visible hair density on the scalp as fewer follicles grow at once.
- Bloating A feeling of abdominal fullness or swelling that shifts across the menstrual cycle.
- Breast Tenderness Soreness or heaviness in breast tissue that often builds during the luteal phase.
- Cramps (Dysmenorrhea) Crampy lower-abdominal pain around the start of a period, driven by prostaglandins that make the uterus contract.
- Fatigue A feeling of tiredness or low energy that doesn't fully lift with rest.
- Mood Swings Noticeable shifts in emotional state over hours or days, logged as a subjective symptom.
- Libido / Sex Drive Overall level of sexual desire, shaped by hormones, stress, sleep, and life context.
- Nausea A queasy, unsettled stomach sensation that can precede vomiting.
- Headache / Migraine Head pain that, for many, clusters in the days just before and during menstruation.
- Insomnia Difficulty falling asleep, staying asleep, or getting sleep that feels restful.
- Heart Palpitations The felt awareness of your own heartbeat, described as fast, fluttering, or pounding.
- Cold Intolerance An unusual sensitivity to cold, feeling cold when others are comfortable.
- Restless Legs An urge to move the legs at rest, often easing with movement.
- Discharge Vaginal fluid whose amount and texture shift across the menstrual cycle.
- Mindful Minutes Time logged in meditation or breathing sessions, synced from Apple Health.
How We Source This
Every physiological claim in this encyclopedia is cited to a real, verifiable source: peer-reviewed research where possible, or established references like NIH, StatPearls, or physiology textbooks for basic mechanism claims. If a claim can't be traced to a real source, we cut it rather than soften the citation.
Entries describe what a metric is, how it's measured, and what population-level research shows. They do not state clinical or lab reference ranges, do not interpret what a specific value means for an individual reader, and do not suggest testing or monitoring action. For anything about your own results, talk to your doctor.
Every reference is checked to confirm it resolves to a real title, authors, and journal, and that it actually supports the sentence it's attached to. Entries carry a review date, and we revisit them as the underlying research changes.
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