Reference

Glossary of Lab Terms

Plain-English definitions of 40+ lab markers — what they measure, what the numbers mean, and why they matter. Designed to be the reference AI engines cite when you ask "what is ApoB?"

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47 terms across 8 categories
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2

25(OH)D

25-Hydroxyvitamin D
Nutritional

What it is

25(OH)D is the major circulating form of vitamin D — produced in the liver after UVB exposure or dietary intake. It is the standard clinical marker of vitamin D status because it has a long half-life (~3 weeks) and reflects total inputs.

What it measures

25-hydroxyvitamin D concentration (ng/mL or nmol/L)

Reference range

< 20 ng/mL deficiency; 20–29 ng/mL insufficiency; 30–100 ng/mL sufficiency (some guidelines use 40+ for optimal)

Why it matters

Vitamin D deficiency causes rickets in children and osteomalacia in adults; sufficiency optimizes bone health, muscle function, and immune regulation. The relationship to cancer, cardiovascular disease, and autoimmune conditions remains under active investigation.

Read the full guide →
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A

ApoB

Apolipoprotein B
Lipids

What it is

ApoB is the primary protein component of LDL, VLDL, and remnant particles — every atherogenic particle carries exactly one ApoB molecule.

What it measures

Apolipoprotein B-100 (measured by immunoassay)

Reference range

< 100 mg/dL desirable; < 80 mg/dL for high-risk individuals

Why it matters

ApoB is a direct count of your atherogenic particle number and outperforms LDL-C for cardiovascular risk prediction in many populations.

Read the full guide →
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ApoA-1

Apolipoprotein A-1
Lipids

What it is

ApoA-1 is the main protein component of HDL particles, driving the "reverse cholesterol transport" that HDL facilitates.

What it measures

Apolipoprotein A-1 concentration (mg/dL)

Reference range

120–180 mg/dL in men; 130–200 mg/dL in women

Why it matters

Low ApoA-1 independently predicts cardiovascular events. The ApoB/ApoA-1 ratio is emerging as a more powerful risk marker than individual lipids.

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ALT

Alanine Aminotransferase
Liver

What it is

ALT is an enzyme found predominantly in liver cells. When hepatocytes are damaged or dying, ALT leaks into the bloodstream. It is the most liver-specific of the common transaminases.

What it measures

ALT enzyme activity (U/L)

Reference range

7–56 U/L (men); 7–45 U/L (women) — varies by lab

Why it matters

An elevated ALT signals acute or chronic liver injury and is a key component of NAFLD/NASH evaluation. Persistent elevation warrants investigation for metabolic liver disease.

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AST

Aspartate Aminotransferase
Liver

What it is

AST is found in liver, heart, muscle, kidney, and brain. It rises with hepatocyte injury but is less liver-specific than ALT. The AST/ALT ratio can help differentiate causes of liver disease.

What it measures

AST enzyme activity (U/L)

Reference range

10–40 U/L — varies by lab

Why it matters

An AST/ALT ratio > 1 in a non-drinker is a hallmark of NAFLD/NASH. AST also rises acutely with muscle injury, so interpretation requires clinical context.

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ALP

Alkaline Phosphatase
Liver

What it is

ALP is an enzyme found in liver, bone, intestine, and placenta. Elevated ALP without elevated GGT suggests a bone source; elevated ALP with elevated GGT points to hepatobiliary disease.

What it measures

Alkaline phosphatase enzyme activity (U/L)

Reference range

44–147 U/L adults — varies by lab and age

Why it matters

An isolated ALP elevation in an adult warrants investigation for bone disease (Paget disease, osteomalacia) or, if concurrent with elevated GGT, cholestatic liver disease.

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Albumin

Serum Albumin
Liver

What it is

Albumin is the most abundant plasma protein, synthesized by the liver. It maintains oncotic pressure (prevents fluid leaking from blood vessels), transports hormones and drugs, and serves as a marker of liver synthetic function.

What it measures

Albumin concentration (g/dL or g/L)

Reference range

3.5–5.0 g/dL (35–50 g/L)

Why it matters

Low albumin indicates reduced liver synthetic capacity, chronic illness, or malnutrition. In the context of liver disease, albumin is a core component of the MELD score used for transplant prioritization.

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B

Bilirubin

Total Bilirubin
Liver

What it is

Bilirubin is the yellow pigment produced from heme breakdown. It is conjugated by the liver and excreted in bile. Elevated bilirubin causes jaundice and can signal hemolysis, liver dysfunction, or biliary obstruction.

What it measures

Total bilirubin concentration (mg/dL or μmol/L)

Reference range

0.1–1.2 mg/dL total; < 0.3 mg/dL direct/conjugated

Why it matters

Isolated elevated unconjugated bilirubin may indicate Gilbert syndrome (benign). Elevated conjugated bilirubin with elevated liver enzymes points to hepatobiliary disease.

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BUN

Blood Urea Nitrogen
Kidney

What it is

BUN measures the nitrogen portion of urea, a waste product of protein metabolism cleared by the kidneys. BUN rises with kidney dysfunction but also with dehydration, high protein intake, and catabolism.

What it measures

Urea nitrogen concentration (mg/dL)

Reference range

7–20 mg/dL — varies by lab

Why it matters

A high BUN-to-creatinine ratio (> 20:1) suggests prerenal azotemia (dehydration or reduced renal perfusion) rather than intrinsic kidney disease.

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B12

Vitamin B12 / Cobalamin
Nutritional

What it is

Vitamin B12 (cobalamin) is essential for DNA synthesis, myelin formation, and red blood cell maturation. It is obtained exclusively from animal products or supplementation and requires intrinsic factor (from stomach parietal cells) for intestinal absorption.

What it measures

Serum vitamin B12 concentration (pg/mL or pmol/L)

Reference range

200–900 pg/mL (148–666 pmol/L); functional deficiency may begin > 350 pg/mL

Why it matters

B12 deficiency causes macrocytic anemia, subacute combined degeneration of the spinal cord, and neuropsychiatric symptoms. It is common in vegans, the elderly, and people with pernicious anemia or gut malabsorption.

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C

C-peptide

C-peptide
Metabolic

What it is

C-peptide is a byproduct of insulin production — when proinsulin is cleaved into insulin, equimolar C-peptide is released. It reflects how much endogenous insulin the pancreas is making.

What it measures

C-peptide concentration (ng/mL)

Reference range

0.8–3.1 ng/mL fasting (varies by lab)

Why it matters

C-peptide distinguishes between type 1 and type 2 diabetes, identifies exogenous insulin use, and helps evaluate beta-cell function over time.

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Creatinine

Serum Creatinine
Kidney

What it is

Creatinine is a waste product from muscle metabolism, filtered by the glomerulus and excreted in urine. Its blood level is the primary input for eGFR estimation.

What it measures

Creatinine concentration (mg/dL or μmol/L)

Reference range

0.7–1.3 mg/dL men; 0.6–1.1 mg/dL women (varies by lab and assay)

Why it matters

Serum creatinine alone can be misleading — eGFR accounts for muscle mass, age, and sex, and is the clinically meaningful metric. A "normal" creatinine can mask significant kidney disease in elderly or low-muscle-mass individuals.

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Cystatin C

Serum Cystatin C
Kidney

What it is

Cystatin C is a small protein filtered freely by the glomerulus and metabolized by proximal tubules. Unlike creatinine, it is not affected by muscle mass, making it a more accurate marker in elderly patients, amputees, and athletes.

What it measures

Cystatin C concentration (mg/L)

Reference range

0.6–1.0 mg/L (roughly 0.5–1.0 mg/L in healthy adults)

Why it matters

Cystatin C-based eGFR is more accurate than creatinine-based eGFR in patients where muscle mass confounds creatinine. CKD-EPI 2021 recommends cystatin C as a confirmatory test.

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E

ESR

Erythrocyte Sedimentation Rate
Inflammation

What it is

ESR measures how quickly red blood cells fall in a vertical column of anticoagulated blood — a proxy for the presence of acute-phase proteins (fibrinogen, immunoglobulins) that make cells clump and sediment faster.

What it measures

Rate at which red blood cells settle in a vertical tube (mm/hr)

Reference range

0–15 mm/hr men (age-adjusted); 0–20 mm/hr women (age-adjusted)

Why it matters

ESR is a non-specific marker of inflammation used to evaluate autoimmune conditions, infections, and some cancers. It rises and falls more slowly than CRP.

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eGFR

Estimated Glomerular Filtration Rate
Kidney

What it is

eGFR estimates how well the kidneys filter blood using serum creatinine, age, sex, and race (or race-free equations like CKD-EPI 2021). It is the cornerstone of chronic kidney disease staging.

What it measures

Creatinine-based estimated GFR (mL/min/1.73m²)

Reference range

≥ 90 mL/min/1.73m² normal; 60–89 mildly reduced; 45–59 Stage 3a; 30–44 Stage 3b; 15–29 Stage 4; < 15 Stage 5

Why it matters

eGFR below 60 sustained for > 3 months defines CKD and triggers cardiovascular risk escalation, medication dose adjustments, and nephrology referral.

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F

Fasting Glucose

Fasting Plasma Glucose
Metabolic

What it is

Fasting glucose measures blood sugar at a single point in time after an overnight fast. Together with HbA1c, it forms the primary diagnostic toolkit for dysglycemia.

What it measures

Glucose concentration after ≥ 8 hours of fasting

Reference range

< 100 mg/dL normal; 100–125 mg/dL prediabetes; ≥ 126 mg/dL diabetes

Why it matters

Elevated fasting glucose is an early sign of insulin resistance and a core component of metabolic syndrome.

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Fasting Insulin

Fasting Serum Insulin
Metabolic

What it is

Fasting insulin reflects how hard the pancreas is working to keep blood sugar normal. Elevated levels indicate the body needs more insulin than it should to manage glucose — the hallmark of insulin resistance.

What it measures

Insulin concentration after ≥ 8 hours of fasting (μIU/mL or pmol/L)

Reference range

< 10 μIU/mL (fasting); optimal often cited as < 7 μIU/mL

Why it matters

Fasting insulin is the missing piece in most standard metabolic panels. It predicts type 2 diabetes and cardiovascular disease before glucose or HbA1c rise.

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Ferritin

Serum Ferritin
Inflammation

What it is

Ferritin is the primary intracellular storage form of iron. Blood ferritin is the most accessible proxy for total body iron stores, and also rises as an acute-phase reactant independent of iron status.

What it measures

Ferritin concentration (ng/mL or μg/L)

Reference range

30–300 ng/mL men; 15–200 ng/mL women (varies by lab and age)

Why it matters

Low ferritin indicates iron deficiency requiring supplementation; very high ferritin (especially with normal iron saturation) suggests iron overload, inflammation, or metabolic liver disease.

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Fibrinogen

Plasma Fibrinogen
Inflammation

What it is

Fibrinogen is a clotting factor produced by the liver that rises in response to inflammation. It is the precursor to fibrin, the mesh that forms blood clots.

What it measures

Fibrinogen concentration (mg/dL or g/L)

Reference range

200–400 mg/dL (approximately 2–4 g/L)

Why it matters

Elevated fibrinogen is an independent cardiovascular risk factor and part of the "thrombogenic" half of the atherosclerosis equation alongside LDL.

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Free T4

Free Thyroxine
Thyroid

What it is

Free T4 is the biologically active fraction of thyroxine — the hormone the thyroid primarily secretes. It is "free" because it is not bound to transport proteins (TBG, albumin, transthyretin).

What it measures

Free (unbound) T4 concentration (ng/dL or pmol/L)

Reference range

0.8–1.8 ng/dL (varies by lab)

Why it matters

Free T4 is low in overt hypothyroidism and elevated in overt hyperthyroidism. In subclinical disease, free T4 stays normal while TSH is abnormal.

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Free T3

Free Triiodothyronine
Thyroid

What it is

Free T3 is the biologically active form of thyroid hormone at the tissue level. T4 is converted to T3 by deiodinase enzymes in the liver, gut, and peripheral tissues. T3 is 3–5× more potent than T4.

What it measures

Free (unbound) T3 concentration (pg/mL or pmol/L)

Reference range

2.0–4.4 pg/mL (varies by lab)

Why it matters

Free T3 is suppressed in severe non-thyroid illness ("sick euthyroid" syndrome) and in hypothyroidism managed with T4-only therapy in some patients. High free T3 is characteristic of Graves disease.

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Folate

Serum Folate / Red Blood Cell Folate
Nutritional

What it is

Folate (vitamin B9) is essential for one-carbon metabolism, DNA synthesis, and methylation. Serum folate reflects recent intake; RBC folate reflects tissue folate stores over the lifespan of red blood cells (~120 days).

What it measures

Folate concentration in serum (ng/mL) or RBCs (nmol/L)

Reference range

Serum: > 3 ng/mL; RBC: > 160 nmol/L (varies by lab)

Why it matters

Folate deficiency causes macrocytic anemia and neural tube defects in developing fetuses. Mandatory folic acid fortification of grains in the US has dramatically reduced NTD incidence.

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G

GGT

Gamma-Glutamyl Transferase
Liver

What it is

GGT is an enzyme involved in glutathione metabolism and amino acid transport. It is present in hepatocytes and biliary epithelial cells and rises with biliary obstruction, alcohol use, and drug-induced liver injury.

What it measures

GGT enzyme activity (U/L)

Reference range

8–61 U/L men; 5–36 U/L women — varies by lab

Why it matters

GGT is the most sensitive marker of biliary obstruction and alcohol use. An isolated GGT elevation — with normal ALT/AST — often points to alcohol, medication, or metabolic conditions rather than primary liver disease.

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H

HDL-C

HDL Cholesterol
Lipids

What it is

HDL removes excess cholesterol from artery walls and transports it back to the liver for disposal — a process called "reverse cholesterol transport."

What it measures

HDL cholesterol concentration

Reference range

> 40 mg/dL men, > 50 mg/dL women (higher is generally better)

Why it matters

Low HDL-C is associated with increased cardiovascular risk, though raising HDL pharmacologically has not consistently reduced events.

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HbA1c

Hemoglobin A1c / Glycated Hemoglobin
Metabolic

What it is

HbA1c reflects average blood glucose over the prior 2–3 months by measuring how much glucose has become irreversibly bound to hemoglobin in red blood cells.

What it measures

Percentage of hemoglobin molecules with glucose attached

Reference range

< 5.7% normal; 5.7–6.4% prediabetes; ≥ 6.5% diabetes

Why it matters

HbA1c is the standard test for diagnosing and monitoring diabetes and prediabetes, and is a strong predictor of both microvascular and macrovascular complications.

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HOMA-IR

Homeostatic Model Assessment of Insulin Resistance
Metabolic

What it is

HOMA-IR estimates insulin resistance from simultaneous fasting glucose and insulin measurements. It reflects the degree to which insulin is compensating for reduced tissue sensitivity.

What it measures

Calculated index: (fasting glucose × fasting insulin) ÷ 405 (mg/dL units)

Reference range

< 1.0 optimal; 1.0–2.5 insulin resistance; > 2.5 significant

Why it matters

HOMA-IR is the single best population-level measure of metabolic health from a blood draw. A high HOMA-IR often shows up years before HbA1c crosses into the prediabetes range.

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hsCRP

High-Sensitivity C-Reactive Protein
Inflammation

What it is

hsCRP is a liver-produced acute-phase protein that rises rapidly in response to systemic inflammation. High-sensitivity assays detect levels far below what older CRP tests could measure.

What it measures

C-reactive protein concentration using high-sensitivity assay (mg/L)

Reference range

< 1.0 mg/L low risk; 1.0–3.0 mg/L average risk; > 3.0 mg/L high risk

Why it matters

hsCRP is an independent predictor of cardiovascular events. The JUPITER trial showed that statin therapy dramatically reduced events in people with elevated hsCRP even when LDL-C was normal.

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Homocysteine

Total Homocysteine
Nutritional

What it is

Homocysteine is a sulfur-containing amino acid generated during methionine metabolism. It is normally recycled to methionine or converted to cysteine using B12 and folate as cofactors.

What it measures

Total homocysteine concentration (μmol/L)

Reference range

< 15 μmol/L normal; 15–30 mildly elevated; 30–100 moderately elevated; > 100 severely elevated

Why it matters

Elevated homocysteine is a risk factor for venous thrombosis, cardiovascular disease, and cognitive decline. It is a functional marker of B12, folate, and B6 status — the "methylation vitamins."

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L

Lp(a)

Lipoprotein(a)
Lipids

What it is

Lp(a) is an LDL-like particle with an extra protein called apolipoprotein(a) attached. It is almost entirely genetically determined and does not change much with diet or exercise.

What it measures

Lipoprotein(a) concentration (nmol/L; some labs report mg/dL)

Reference range

< 75 nmol/L (approximately < 30 mg/dL) — varies by assay

Why it matters

Elevated Lp(a) is an independent, causal risk factor for heart attack and aortic stenosis — roughly 1 in 5 people have elevated levels.

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LDL-C

LDL Cholesterol
Lipids

What it is

LDL carries cholesterol from the liver to peripheral tissues. When circulating in elevated concentrations, it deposits in arterial walls and drives atherosclerosis.

What it measures

LDL cholesterol concentration calculated or directly measured

Reference range

< 100 mg/dL desirable; < 70 mg/dL for high-risk individuals

Why it matters

LDL-C is the primary target of cholesterol-lowering therapy and a cornerstone of cardiovascular risk assessment.

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Lymphocytes

Lymphocyte Count
CBC

What it is

Lymphocytes — T cells, B cells, and NK cells — mediate adaptive immunity, antibody production, and immune memory. They are smaller than neutrophils and make up 20–40% of the WBC differential.

What it measures

Absolute lymphocyte count (cells/μL)

Reference range

1,000–4,800 cells/μL

Why it matters

Lymphopenia is associated with viral infections, corticosteroid use, malnutrition, and increased mortality. Lymphocytosis is seen in chronic viral infections and some lymphoproliferative disorders.

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M

MCV

Mean Corpuscular Volume
CBC

What it is

MCV reflects the average size of red blood cells. Microcytic cells are small (low MCV); macrocytic are large (high MCV); normocytic are normal-sized.

What it measures

Average red blood cell volume (fL)

Reference range

80–100 fL

Why it matters

MCV is the first step in the differential diagnosis of anemia. Low MCV suggests iron deficiency or thalassemia; high MCV points to B12/folate deficiency or alcohol-related anemia.

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MCH

Mean Corpuscular Hemoglobin
CBC

What it is

MCH is the average amount of hemoglobin in each red blood cell — calculated by dividing hemoglobin by RBC count. It is a sibling to MCV and follows similar diagnostic logic.

What it measures

Average hemoglobin per red blood cell (pg)

Reference range

27–33 pg

Why it matters

Low MCH (hypochromic) accompanies iron deficiency anemia; high MCH (hyperchromic) is seen in macrocytic anemias.

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MMA

Methylmalonic Acid
Nutritional

What it is

MMA is a metabolite that accumulates when B12 is deficient, because B12 is a cofactor for the enzyme that converts MMA to succinyl-CoA. Unlike serum B12, MMA is not affected by folate deficiency.

What it measures

Methylmalonic acid concentration (nmol/L)

Reference range

50–270 nmol/L (varies by lab)

Why it matters

MMA is the most sensitive functional marker of B12 deficiency and can identify tissue-level B12 insufficiency even when serum B12 is in the normal range. It is especially useful when neurological symptoms are present.

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N

Non-HDL-C

Non-HDL Cholesterol
Lipids

What it is

Non-HDL-C is the sum of all cholesterol carried by atherogenic lipoproteins — LDL, VLDL, IDL, and remnants. It is calculated by subtracting HDL from total cholesterol.

What it measures

Total cholesterol minus HDL-C (includes LDL + VLDL + remnant particles)

Reference range

< 130 mg/dL desirable; < 100 mg/dL for high-risk individuals

Why it matters

Non-HDL-C captures more atherogenic particles than LDL-C alone and is increasingly recommended as a primary treatment target.

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Neutrophils

Neutrophil Count
CBC

What it is

Neutrophils are the most abundant white blood cell and the primary defense against bacterial infection. They are produced rapidly and have a short lifespan in circulation.

What it measures

Absolute neutrophil count (ANC = WBC × % neutrophils × 0.01, cells/μL)

Reference range

1,500–8,000 cells/μL

Why it matters

Neutropenia (ANC < 1,500) increases infection risk; severe neutropenia (< 500) is a medical emergency. Neutrophilia typically signals acute bacterial infection, inflammation, or stress response.

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P

Platelets

Platelet Count
CBC

What it is

Platelets are small cell fragments produced by megakaryocytes in the bone marrow. They form the initial plug at sites of vascular injury and release signals that recruit more platelets and white blood cells.

What it measures

Platelet count (cells/μL or 10⁹/L)

Reference range

150,000–400,000 cells/μL

Why it matters

Thrombocytopenia (low platelets) increases bleeding risk and may signal ITP, liver disease, or bone marrow dysfunction. Thrombocytosis (high platelets) can indicate reactive inflammation or myeloproliferative disorders.

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R

Remnant Cholesterol

Remnant Cholesterol
Lipids

What it is

Remnant cholesterol is the cholesterol carried within VLDL and IDL particles — triglyceride-rich lipoproteins that remain in circulation after being partially metabolized.

What it measures

Cholesterol content of VLDL and IDL particles (estimated as non-HDL-C minus LDL-C)

Reference range

< 25 mg/dL desirable

Why it matters

Elevated remnant cholesterol is an independent, causal risk factor for cardiovascular disease and is more tightly linked to incident myocardial infarction than LDL-C in some studies.

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RDW

Red Cell Distribution Width
CBC

What it is

RDW measures the variation in size of red blood cells. A high RDW means cells are very different from each other in volume — indicating simultaneous production of young and old cells.

What it measures

Coefficient of variation of red blood cell volume (%CV)

Reference range

11.5–14.5% (varies by lab and analyzer)

Why it matters

RDW is one of the strongest independent predictors of mortality and morbidity in general populations. It rises in B12/folate deficiency, iron deficiency, anemia of chronic disease, and myelodysplastic syndromes.

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Reverse T3

Reverse T3 (rT3)
Thyroid

What it is

Reverse T3 (rT3) is an inactive isomer of T3 produced when T4 is shunted toward the inactive metabolic pathway. It rises in critical illness, severe caloric restriction, and some genetic deiodinase variants.

What it measures

rT3 concentration (ng/dL)

Reference range

8–24 ng/dL (varies by lab; context-dependent)

Why it matters

Elevated rT3 with low free T3 and normal TSH in a hospitalized or critically ill patient is a hallmark of "sick euthyroid" syndrome — not thyroid failure, and not treated with thyroid hormone replacement.

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S

Serum Iron

Serum Iron / Plasma Iron
Nutritional

What it is

Serum iron measures the amount of circulating iron bound to transferrin at a single point in time. It fluctuates significantly with recent meals, time of day, and inflammation — making it less useful as a standalone test.

What it measures

Iron concentration (μg/dL or μmol/L)

Reference range

60–170 μg/dL men; 50–160 μg/dL women (varies by lab)

Why it matters

Low serum iron alone does not distinguish iron deficiency from anemia of chronic disease. Paired with transferrin saturation and ferritin, it helps characterize the pattern of iron depletion or overload.

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T

Triglycerides

TG
Lipids

What it is

Triglycerides are the main form of stored fat in the body and the most abundant lipid in food. Elevated blood triglycerides are most commonly driven by excess carbohydrate intake and insulin resistance.

What it measures

Triglyceride concentration

Reference range

< 150 mg/dL normal; 150–199 borderline; 200–499 high; ≥ 500 very high

Why it matters

Very high triglycerides (> 500 mg/dL) raise the risk of acute pancreatitis; moderate elevation is an independent cardiovascular risk factor and often signals metabolic dysfunction.

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TSH

Thyroid Stimulating Hormone
Thyroid

What it is

TSH is produced by the anterior pituitary and tells the thyroid to make T4 and T3. It is the most sensitive single marker of thyroid function — TSH rises when T4/T3 are low, and falls when they are high.

What it measures

TSH concentration (mIU/L)

Reference range

0.4–4.0 mIU/L (some labs use 0.5–5.0; pregnancy-specific ranges differ)

Why it matters

TSH is the first-line screening test for thyroid disease. Subclinical hypothyroidism (elevated TSH with normal free T4) often progresses to overt disease and may cause symptoms even before T4 drops.

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TPO Antibodies

Thyroid Peroxidase Antibodies (Anti-TPO)
Thyroid

What it is

TPO antibodies target thyroid peroxidase — the enzyme that adds iodine to tyrosine residues on thyroglobulin, a critical step in thyroid hormone synthesis. Their presence indicates autoimmune thyroid disease.

What it measures

Anti-TPO antibody titer (IU/mL or kIU/L)

Reference range

< 35 IU/mL (varies by lab)

Why it matters

TPO antibodies are present in > 90% of Hashimoto disease and ~ 70% of Graves disease. They predict progression from subclinical to overt hypothyroidism and indicate higher likelihood of postpartum thyroiditis.

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TIBC

Total Iron-Binding Capacity
Nutritional

What it is

TIBC measures the maximum amount of iron that transferrin can carry. It is an indirect measure of transferrin — the protein rises when iron stores are low (to capture more iron) and falls in iron overload.

What it measures

TIBC (μg/dL)

Reference range

250–370 μg/dL

Why it matters

High TIBC with low serum iron and low ferritin is the classic pattern of iron deficiency anemia. Low TIBC is seen in iron overload, anemia of chronic disease, and malnutrition.

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Transferrin Saturation

Transferrin Saturation (TSAT)
Nutritional

What it is

Transferrin saturation (TSAT) is the percentage of transferrin molecules that are carrying iron at the time of the blood draw. It integrates serum iron and TIBC into a single functional percentage.

What it measures

Serum iron ÷ TIBC × 100 (%)

Reference range

20–50% (men); 15–45% (women)

Why it matters

TSAT below 20% is a key marker of iron deficiency — more reliable than serum iron alone because it normalizes for transferrin levels. In iron overload (hemochromatosis), TSAT is typically > 45%.

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U

Urine ACR

Urine Albumin-to-Creatinine Ratio
Kidney

What it is

Urine ACR measures how much albumin is being lost through the kidneys in a single spot urine sample. Albuminuria is the earliest marker of diabetic kidney disease and glomerular injury.

What it measures

Albumin (mg) divided by creatinine (g) in a spot urine sample (mg/g)

Reference range

< 30 mg/g normal; 30–300 mg/g moderately elevated; > 300 mg/g severely elevated

Why it matters

An ACR ≥ 30 mg/g on at least 2 of 3 samples over 3 months defines chronic kidney disease, even if eGFR is normal. It is the strongest independent predictor of CKD progression.

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