Blood Test Markers Glossary: Every Marker, Grouped by Body System

A lab report is mostly acronyms. This glossary turns them back into plain English. Every marker below links to its own guide — what it measures, the reference ranges the labs and guidelines actually use, and how to track it over time — grouped by the body system it belongs to so you can find yours fast.

If you're new to reading a lab report at all, start with how to read your blood test results — it covers units, reference ranges, and why the trend matters more than any single value. This page is the index that sits underneath it.

What do your blood test markers mean?

A blood test marker is a single substance the lab measured in your sample — a cholesterol particle, an enzyme, a hormone, a vitamin.¹ On its own, each one is a narrow window into one system: your lipids, your blood sugar, your thyroid, your liver, and so on. No single marker is a verdict, and "in range" isn't the same as "optimal" — the meaningful signal is how a marker moves across several draws.² Use the sections below to find a marker, read its one-line summary, then open its full guide for the ranges and context. We don't quote "optimal" numbers here on purpose: those are debated, vary by lab and by person, and belong on each marker's own page.

The library is still growing — more markers are on the roadmap — but here's everything live today.

Cardiovascular and lipid markers

The lipid panel and its newer companions estimate cardiovascular risk.

• ApoB — a direct count of the atherogenic particles most likely to lodge in an artery wall; many specialists consider it a sharper readout than LDL alone.
• LDL cholesterol — the familiar "bad cholesterol," one core input into cardiovascular risk.
• HDL cholesterol — the "good cholesterol," best read in context alongside the rest of the panel.
• Triglycerides — a blood fat sensitive to recent meals and alcohol, so fasting status changes the number.
• Lp(a) — a largely inherited particle that adds cardiovascular risk independent of LDL.

Metabolic and glycemic markers

How your body is handling blood sugar over the short and long term.

• HbA1c — an estimate of your average blood sugar over roughly the past three months, steadier than any single reading.
• Fasting glucose — your blood sugar after an overnight fast, a snapshot of glucose control.

Thyroid markers

The thyroid panel, usually read as a set rather than one number.

• TSH — the pituitary's signal to the thyroid, and the usual first-line screen.
• Free T4 — the main circulating thyroid hormone available to your tissues.
• Free T3 — the active thyroid hormone, read alongside TSH and Free T4.

Hormone markers

Sex and adrenal hormones — interpretation here is strongly age- and sex-dependent.

• Testosterone — the primary androgen, relevant in both sexes.
• Estradiol — the main estrogen; levels shift across the cycle and life stage.
• DHEA-S — an adrenal androgen precursor whose "normal" range drops steeply with age.

Liver markers

Enzymes and proteins that reflect how the liver is working.

• ALT — a liver enzyme that rises when liver cells are stressed or damaged.
• AST — a companion enzyme; the AST-to-ALT ratio adds context.
• ALP — alkaline phosphatase, driven by both liver and bone.
• Albumin — the main protein your liver makes, reflecting liver synthesis, nutrition, and inflammation (also a biological-age input).

Kidney markers

How well your kidneys are filtering.

• eGFR and creatinine — a waste product (creatinine) and the estimated filtration rate calculated from it; together they track kidney function.

Inflammation markers

Signals of low-grade, body-wide inflammation and related risk.

• hs-CRP — a high-sensitivity measure of background inflammation.
• Homocysteine — an amino acid tied to B-vitamin status and cardiovascular risk; B12 and folate help keep it in check.
• Ferritin — your iron-storage protein; low can signal iron deficiency, but it also rises with inflammation.

Nutrient markers

Vitamins and fats that reflect diet and supplementation.

• Vitamin D (25-OH) — the storage form labs measure to gauge your vitamin D status.
• Vitamin B12 — essential for nerves and red blood cells, with a diagnostic "gray zone" that sometimes needs confirmatory tests.
• Omega-3 index — the share of omega-3 fats in your red blood cell membranes.

Complete blood count and biological-age markers

Indices from the CBC that double as quiet aging signals.

• RDW — red cell distribution width, a measure of how variable your red blood cells' size is, and a useful nutrition and aging signal.

Several markers scattered across the sections above — albumin, fasting glucose, hs-CRP, ALP, creatinine, and RDW — are also the inputs to the Levine PhenoAge algorithm.³ If you're curious how a handful of routine labs get turned into a single number, see biological age explained.

Where Libby fits

A glossary tells you what each marker means once. The harder problem is keeping your own values for all of them in one place, so you can see each one move over years instead of meeting it fresh on every new PDF. That's the job Libby is built for: drop in a lab report and it reads every marker, reconciles the units, and files each one onto a single timeline against the range printed on that report. It becomes a personal health record you own for life and can export anytime.

If you want every marker in this glossary tracked against your own history, start your record — the first upload takes about a minute.

Educational content, not medical advice. This glossary is for general information and personal record-keeping. It isn't a diagnosis or a treatment plan, and reference ranges vary by lab and by person. Always talk to a qualified healthcare professional about your results and any decisions that follow from them.