What it is: An albumin blood test measures the level of albumin, a protein made by the liver that maintains fluid balance in the bloodstream and helps transport hormones, vitamins, and other substances throughout the body.
Why it's ordered: Ordered when liver or kidney disease is suspected, or to assess nutritional status. It's commonly included in a comprehensive metabolic panel or liver panel rather than run alone.
What it detects: Low albumin (hypoalbuminemia) can point to liver disease, kidney disease (excess protein loss through urine), malnutrition, inflammation, or malabsorption. High albumin is less diagnostically significant and is usually just a sign of dehydration.
Collection & prep: A standard blood draw from a vein in the arm. No special preparation is required, though fasting may be requested if albumin is being tested alongside other panel components, and certain medications can affect results.
Results:
Low – may indicate liver disease, kidney disease, inflammation, or poor protein intake
Normal – albumin production and loss are balanced
High – usually reflects dehydration rather than an underlying disease
Possible complications of low albumin: Significantly low albumin (below about 2.0 g/dL) can lead to edema, since albumin normally keeps fluid inside blood vessels. An abnormal result on its own isn't diagnostic and typically prompts further testing to pinpoint the cause.
Quick Guide: Alkaline phosphatase (ALP) Blood Test
What it is: An alkaline phosphatase (ALP) test measures the level of ALP, an enzyme found mainly in the liver, bones, kidneys, and intestines, in a blood sample.
Why it's ordered: Ordered to screen for or monitor liver and bile duct conditions or bone disorders, often as part of a comprehensive metabolic panel or liver (hepatic) function panel rather than in isolation.
What it detects: Elevated ALP can indicate liver disease, bile duct obstruction, or bone disorders such as Paget's disease or vitamin D deficiency affecting bone metabolism. A standard ALP test can't tell which tissue the enzyme came from; a follow-up ALP isoenzyme test can help localize the source.
Collection & prep: A standard blood draw from a vein in the arm. Fasting isn't always required for a standalone ALP test, but 6-12 hours of fasting is often requested when it's part of a larger panel, and isoenzyme testing usually requires fasting.
Results:
High – suggests liver disease, bile duct issues, or a bone disorder; needs follow-up testing to confirm the source
Normal – typically 30–120 IU/L in adults, though ranges vary by lab, age, and sex
Low – less common; can reflect malnutrition or certain genetic or metabolic conditions
Possible complications of underlying ALP-related conditions: About 1 in 20 healthy people has an ALP result outside the standard range without any disease, so an abnormal result alone isn't a diagnosis. Persistently high levels typically prompt additional liver panel tests, an ALP isoenzyme test, or imaging to identify the cause.
Quick Guide: Aminotransferase, alanine (ALT) Blood Test
What it is: An ALT (alanine aminotransferase) test measures the level of ALT, an enzyme found mainly in the liver, in a blood sample.
Why it's ordered: Ordered to evaluate liver health, usually as part of a liver panel or comprehensive metabolic panel, when a provider suspects liver damage from hepatitis, fatty liver disease, medication effects, or alcohol use, or to monitor a known liver condition.
What it detects: ALT leaks into the blood when liver cells are damaged, so elevated levels point to liver injury. Because ALT is more concentrated in the liver than AST, it's considered a fairly specific marker of liver (rather than muscle or heart) damage.
Collection & prep: A standard blood draw from a vein in the arm. ALT is rarely tested alone; when it's part of a larger panel, fasting may be requested, and certain medications can affect results.
Results:
High – typically above 45 IU/L in adults; suggests liver cell damage from hepatitis, fatty liver disease, or medication/alcohol effects
Normal – roughly 0–45 IU/L, though ranges vary by lab
Possible complications of liver damage: A single elevated ALT doesn't diagnose a specific disease — it's usually interpreted alongside AST, ALP, and GGT to narrow down the cause, and repeat testing can track whether a liver condition is progressing or resolving.
Quick Guide: Aminotransferase, aspartate (AST) Blood Test
What it is: An AST (aspartate aminotransferase) test measures the level of AST, an enzyme found in the liver, heart, muscles, and other tissues, in a blood sample.
Why it's ordered: Ordered to assess liver health, typically alongside ALT in a liver panel, when a provider suspects liver damage, or to help evaluate other conditions affecting muscle or heart tissue.
What it detects: AST leaks into the blood when liver cells (or other AST-containing tissues, like heart or skeletal muscle) are damaged. Because AST is less liver-specific than ALT, comparing the two — the AST-to-ALT ratio — helps distinguish liver injury from other causes and can hint at alcohol-related versus other liver damage.
Collection & prep: A standard blood draw from a vein in the arm. As with ALT, no special prep is typically required unless it's part of a larger fasting panel.
Results:
High – typically above 35 IU/L in adults; suggests damage to the liver or another AST-containing tissue
Normal – roughly 0–35 IU/L, though ranges vary by lab
Possible complications of liver or muscle damage: AST alone can't pinpoint the source of damage since it's present in several organs; providers typically interpret it alongside ALT, CK, and clinical symptoms to determine whether the cause is hepatic, cardiac, or muscular.
Quick Guide: Antinuclear antibodies (ANA) Blood Test
What it is: An ANA (antinuclear antibody) test detects autoantibodies in the blood that mistakenly target the nucleus of the body's own cells, most often measured by immunofluorescence or ELISA.
Why it's ordered: Ordered when a provider suspects an autoimmune disorder such as lupus, Sjogren syndrome, or mixed connective tissue disease, typically based on symptoms like joint pain, unexplained rashes, or fatigue.
What it detects: The presence and amount of antinuclear antibodies. A positive result supports further testing for specific autoantibodies tied to particular autoimmune conditions, since ANA alone isn't specific to any one disease.
Collection & prep: A standard blood draw from a vein in the arm. No special preparation is needed, though certain medications (including some seizure and heart drugs) can affect accuracy, so current medications should be disclosed beforehand.
Results:
Positive – antinuclear antibodies detected; doesn't confirm a disease on its own, since some healthy people test weakly positive
Negative – no significant antinuclear antibodies detected
Possible complications of autoimmune disease: A positive ANA is one piece of a larger picture — providers combine it with symptoms, physical exam findings, and more specific antibody tests (e.g., anti-dsDNA) to diagnose or rule out a particular autoimmune condition.
What it is: A basophil count measures the number of basophils — a type of white blood cell involved in allergic responses — typically as part of a complete blood count (CBC) with differential.
Why it's ordered: Ordered alongside a CBC with differential when evaluating allergic reactions, unexplained inflammation, or certain blood disorders.
What it detects: Basophils release histamine during allergic reactions and heparin, which helps prevent excessive blood clotting. Elevated levels (basophilia) can suggest allergic conditions or, less commonly, myeloproliferative blood disorders; low levels are less clinically significant on their own.
Collection & prep: A standard blood draw from a vein in the arm, as part of a CBC with differential. No special preparation is needed.
Results:
High – basophilia; can be linked to allergic reactions or, rarely, myeloproliferative disorders
Normal – typically 0.5–1% of total white blood cells
Possible complications: Basophil counts are rarely abnormal in isolation and are usually interpreted together with the rest of the white blood cell differential rather than as a standalone diagnostic clue.
Quick Guide: Bicarbonate (carbon dioxide) Blood Test
What it is: A bicarbonate (carbon dioxide) test measures the level of bicarbonate in the blood, an electrolyte that helps maintain the body's acid-base balance.
Why it's ordered: Usually ordered as part of an electrolyte panel, basic metabolic panel, or comprehensive metabolic panel to evaluate acid-base balance, kidney function, or unexplained symptoms like vomiting, breathing difficulty, or fatigue.
What it detects: Bicarbonate helps buffer acids and moves carbon dioxide through the bloodstream. Abnormal levels can point to kidney disease, breathing disorders, severe vomiting or diarrhea, or metabolic acid-base imbalances.
Collection & prep: A standard blood draw from a vein in the arm, typically alongside sodium, potassium, and chloride. No special prep is usually required unless it's part of a fasting panel.
Results:
High – may reflect metabolic alkalosis or a compensatory response to a breathing disorder
Low – may reflect metabolic acidosis, kidney disease, or fluid loss from vomiting/diarrhea
Normal – acid-base balance appears stable
Possible complications of an imbalance: Significant bicarbonate abnormalities can affect the heart, muscles, and nervous system, so single abnormal results are usually followed up with repeat testing or blood gas analysis alongside the person's symptoms.
What it is: A bilirubin test measures the level of bilirubin — a yellow pigment produced when red blood cells break down — in the blood, usually as total, direct (conjugated), and indirect (unconjugated) values.
Why it's ordered: Ordered as part of a liver panel when a provider suspects liver disease, bile duct blockage, or a condition causing excess red blood cell breakdown (hemolysis), or when someone shows signs of jaundice.
What it detects: Bilirubin is normally processed by the liver and excreted in bile. Elevated levels can point to liver dysfunction, bile duct obstruction, or increased red blood cell destruction, depending on whether the direct or indirect fraction is elevated.
Collection & prep: A standard blood draw from a vein in the arm, usually alongside other liver function tests. No special preparation is typically required.
Results:
High total/indirect – often reflects increased red blood cell breakdown or reduced liver uptake
High direct – often points to bile duct obstruction or liver processing problems
Normal – typically 2 to 17 micromoles/L (roughly 0.1–1.2 mg/dL), though ranges vary by lab
Possible complications of high bilirubin: Persistently elevated bilirubin causes jaundice (yellowing of skin and eyes) and, in newborns, can in rare severe cases lead to kernicterus; adults with abnormal results are usually evaluated further to determine the underlying liver, bile duct, or blood-related cause.
What it is: A BUN (blood urea nitrogen) test measures the amount of urea nitrogen, a waste product from protein breakdown, in the blood as a screen for kidney function.
Why it's ordered: Ordered to evaluate kidney function, often alongside creatinine, when symptoms like fatigue, swelling, or changes in urination raise concern, or as part of routine metabolic panels.
What it detects: Urea nitrogen is normally filtered out by the kidneys and excreted in urine. Elevated BUN can point to reduced kidney function, dehydration, heart failure, or GI bleeding; the BUN-to-creatinine ratio helps distinguish these causes.
Collection & prep: A standard blood draw from a vein in the arm, usually as part of a basic or comprehensive metabolic panel. Fasting may be requested if paired with glucose testing.
Results:
High – typically above 20–24 mg/dL; can reflect reduced kidney function, dehydration, heart failure, or high protein intake
Low – less common; can reflect liver disease, malnutrition, or overhydration
Normal – roughly 6–24 mg/dL, though ranges vary by lab
Possible complications of kidney dysfunction: A single elevated BUN doesn't diagnose kidney disease on its own — providers typically pair it with creatinine and eGFR, and BUN over 100 mg/dL points to more severe kidney impairment requiring urgent evaluation.
What it is: A C-reactive protein (CRP) test measures the level of CRP, a protein the liver produces in response to inflammation, in the blood.
Why it's ordered: Ordered to help detect infection or inflammation, assess autoimmune disease activity, or, in a high-sensitivity form, estimate cardiovascular risk.
What it detects: CRP rises within hours of tissue injury, infection, or inflammation and falls as the underlying cause resolves, making it useful for tracking infection or inflammatory disease activity over time, though it doesn't identify the specific cause.
Collection & prep: A standard blood draw from a vein in the arm. No special preparation is typically required for a standard CRP test.
Results:
High – suggests active inflammation or infection somewhere in the body; doesn't identify the location or cause on its own
Normal – generally below about 1 mg/dL (lab-dependent); doesn't rule out localized or mild inflammation
Possible complications of underlying inflammation: Because CRP is non-specific, an elevated result typically prompts further evaluation — symptoms, exam findings, and additional tests — to identify the source rather than serving as a standalone diagnosis.
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