Quick Guide: Complete blood cell count (CBC) Blood Test
What it is: A complete blood count (CBC) measures the amounts and sizes of red blood cells, white blood cells, hemoglobin, and platelets in a blood sample; a CBC "with differential" also breaks down the different types of white blood cells.
Why it's ordered: Ordered as routine health screening or to help diagnose and monitor conditions like anemia, infection, inflammation, bleeding disorders, or blood cancers.
What it detects: Abnormal red blood cell counts can indicate anemia or polycythemia; abnormal white blood cell counts or differential can indicate infection, inflammation, allergic reactions, or leukemia; abnormal platelet counts can indicate bleeding or clotting disorders.
Collection & prep: A standard blood draw from a vein in the arm. No special preparation is typically required.
Results:
Abnormal red cell values – may suggest anemia or a red blood cell overproduction disorder
Abnormal white cell values – may suggest infection, inflammation, or a blood cancer, depending on which cell type is affected
Abnormal platelet count – may suggest a bleeding or clotting risk
Possible complications: A CBC is a screening tool rather than a diagnosis — abnormal results typically prompt a peripheral blood smear or further targeted testing (like iron studies or bone marrow evaluation) to identify the specific cause.
Quick Guide: Creatine kinase (CK or CPK) Blood Test
What it is: A creatine kinase (CK or CPK) test measures the level of CK, an enzyme found mainly in skeletal muscle, heart muscle, and the brain, in the blood.
Why it's ordered: Ordered to evaluate suspected muscle damage, heart attack, or muscle disorders, or to monitor conditions like rhabdomyolysis or statin-related muscle effects.
What it detects: CK leaks into the blood when muscle cells are damaged. Elevated levels can reflect an injury or intense exercise, a heart attack (historically tracked via the CK-MB isoenzyme), or a muscle disease; isoenzyme testing can help identify which tissue is affected.
Collection & prep: A standard blood draw from a vein in the arm. Strenuous exercise shortly before the test can elevate results, so providers may ask about recent activity when interpreting levels.
Results:
High – suggests muscle, heart, or brain tissue damage; can also reflect intense exercise or certain medications
Normal – no significant recent muscle damage detected
Possible complications of muscle damage: Very high CK levels can signal rhabdomyolysis, a serious breakdown of muscle tissue that can lead to acute kidney injury if untreated, so markedly elevated results are followed up promptly.
What it is: A creatinine test measures the level of creatinine, a waste product from normal muscle breakdown, in the blood as a marker of kidney function.
Why it's ordered: Ordered to evaluate kidney function, often alongside BUN, as part of routine metabolic panels or when kidney disease is suspected based on symptoms or risk factors like diabetes or high blood pressure.
What it detects: Creatinine is normally filtered out by the kidneys at a steady rate; when kidney filtration declines, creatinine builds up in the blood. It's used to calculate the estimated glomerular filtration rate (eGFR), a more precise measure of kidney function.
Collection & prep: A standard blood draw from a vein in the arm. No special preparation is typically required.
Results:
High – suggests reduced kidney filtration; typical adult ranges are roughly 0.6–1.1 mg/dL (women) and 0.7–1.3 mg/dL (men)
eGFR below 60 for three months or more indicates chronic kidney disease; below 15 indicates kidney failure
Possible complications of reduced kidney function: Because creatinine is affected by muscle mass, age, and other non-kidney factors, providers typically rely on eGFR rather than creatinine alone, and declining kidney function is monitored over time alongside symptoms and other kidney markers.
What it is: An electrolyte panel measures the levels of several electrically charged minerals in the blood — commonly sodium, potassium, chloride, and bicarbonate, sometimes with calcium and magnesium — together in one blood draw.
Why it's ordered: Ordered as routine screening or to evaluate symptoms like dehydration, muscle weakness, irregular heartbeat, or confusion, and to monitor kidney disease, heart failure, or diuretic use.
What it detects: Electrolytes regulate fluid balance, nerve and muscle function, and acid-base balance. The panel is read as a pattern — a shift in one electrolyte often triggers compensatory shifts in others — rather than as isolated numbers.
Collection & prep: A standard blood draw from a vein in the arm, often as part of a basic or comprehensive metabolic panel. No special preparation is usually required unless it's part of a fasting panel.
Results:
Abnormal pattern – can point to dehydration, kidney dysfunction, or an acid-base disorder, depending on which values shift and in which direction
Normal – fluid balance and acid-base status appear stable
Possible complications of an imbalance: Significant electrolyte abnormalities can affect the heart, brain, and muscles; results that don't match a person's symptoms are often repeated, and severe abnormalities (e.g., with chest pain, confusion, or severe weakness) warrant urgent evaluation.
What it is: An eosinophil count measures the number of eosinophils, a type of white blood cell involved in fighting parasites and allergic responses, typically as part of a CBC with differential.
Why it's ordered: Ordered alongside a CBC with differential to evaluate suspected allergic reactions, asthma, parasitic infections, or certain autoimmune and blood conditions.
What it detects: Eosinophils rise (eosinophilia) with parasitic infections, allergic conditions, certain skin disorders, and some cancers; they fall (eosinopenia) with acute stress, inflammation, or corticosteroid use.
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 – eosinophilia; linked to allergies, parasitic infection, asthma, or certain other conditions
Normal – typically 1–4% of total white blood cells
Possible complications: Persistently high eosinophil counts can be a sign of an underlying condition needing further workup, such as a parasitic infection (which may prompt stool ova and parasite testing) or an eosinophilic disorder.
What it is: An eosinophil count measures the number of eosinophils, a type of white blood cell involved in fighting parasites and allergic responses, typically as part of a CBC with differential.
Why it's ordered: Ordered alongside a CBC with differential to evaluate suspected allergic reactions, asthma, parasitic infections, or certain autoimmune and blood conditions.
What it detects: Eosinophils rise (eosinophilia) with parasitic infections, allergic conditions, certain skin disorders, and some cancers; they fall (eosinopenia) with acute stress, inflammation, or corticosteroid use.
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 – eosinophilia; linked to allergies, parasitic infection, asthma, or certain other conditions
Normal – typically 1–4% of total white blood cells
Possible complications: Persistently high eosinophil counts can be a sign of an underlying condition needing further workup, such as a parasitic infection (which may prompt stool ova and parasite testing) or an eosinophilic disorder.
Quick Guide: Erythrocyte sedimentation rate (ESR) Blood Test
What it is: An ESR (erythrocyte sedimentation rate) test, or "sed rate," measures how quickly red blood cells settle to the bottom of a test tube over one hour as a general marker of inflammation.
Why it's ordered: Ordered to help detect or monitor inflammatory conditions such as rheumatoid arthritis, other autoimmune diseases, or infections, often alongside CRP.
What it detects: Inflammation increases certain blood proteins that cause red blood cells to clump and settle faster. ESR doesn't identify where or why inflammation is occurring — it's a nonspecific signal used to screen for or track inflammatory activity over time.
Collection & prep: A standard blood draw from a vein in the arm. No special preparation is required.
Results:
High – suggests inflammation somewhere in the body; can also rise with age, infection, or other non-inflammatory conditions
Normal – roughly 0–20 mm/hr in men and 0–30 mm/hr in women, varying by age and lab
Possible complications: ESR can't confirm or rule out a specific condition on its own; it's most useful for tracking inflammation over time and is typically interpreted alongside symptoms and other tests like CRP.
Quick Guide: Erythrocyte sedimentation rate (ESR) Blood Test
What it is: An ESR (erythrocyte sedimentation rate) test, or "sed rate," measures how quickly red blood cells settle to the bottom of a test tube over one hour as a general marker of inflammation.
Why it's ordered: Ordered to help detect or monitor inflammatory conditions such as rheumatoid arthritis, other autoimmune diseases, or infections, often alongside CRP.
What it detects: Inflammation increases certain blood proteins that cause red blood cells to clump and settle faster. ESR doesn't identify where or why inflammation is occurring — it's a nonspecific signal used to screen for or track inflammatory activity over time.
Collection & prep: A standard blood draw from a vein in the arm. No special preparation is required.
Results:
High – suggests inflammation somewhere in the body; can also rise with age, infection, or other non-inflammatory conditions
Normal – roughly 0–20 mm/hr in men and 0–30 mm/hr in women, varying by age and lab
Possible complications: ESR can't confirm or rule out a specific condition on its own; it's most useful for tracking inflammation over time and is typically interpreted alongside symptoms and other tests like CRP.
What it is: A ferritin test measures the level of ferritin, a protein that stores iron inside cells, in the blood as an indicator of the body's iron reserves.
Why it's ordered: Ordered to help diagnose iron deficiency or iron overload, evaluate unexplained fatigue or anemia, or monitor known iron-related conditions.
What it detects: Ferritin is generally a better marker of stored iron than serum iron alone. Low ferritin points to depleted iron stores, often before anemia becomes apparent; high ferritin can reflect iron overload or, since ferritin also rises with inflammation, an unrelated inflammatory condition.
Collection & prep: A standard blood draw from a vein in the arm. No special preparation is typically required.
Results:
Low – suggests iron deficiency; below roughly 10–30 ng/mL depending on the lab and clinical context
High – can reflect iron overload (e.g., hemochromatosis) or inflammation unrelated to iron status
Possible complications of an iron imbalance: Untreated iron deficiency can cause fatigue, weakened immunity, and difficulty concentrating, while iron overload can damage the liver, heart, and other organs over time if not managed.
What it is: A ferritin test measures the level of ferritin, a protein that stores iron inside cells, in the blood as an indicator of the body's iron reserves.
Why it's ordered: Ordered to help diagnose iron deficiency or iron overload, evaluate unexplained fatigue or anemia, or monitor known iron-related conditions.
What it detects: Ferritin is generally a better marker of stored iron than serum iron alone. Low ferritin points to depleted iron stores, often before anemia becomes apparent; high ferritin can reflect iron overload or, since ferritin also rises with inflammation, an unrelated inflammatory condition.
Collection & prep: A standard blood draw from a vein in the arm. No special preparation is typically required.
Results:
Low – suggests iron deficiency; below roughly 10–30 ng/mL depending on the lab and clinical context
High – can reflect iron overload (e.g., hemochromatosis) or inflammation unrelated to iron status
Possible complications of an iron imbalance: Untreated iron deficiency can cause fatigue, weakened immunity, and difficulty concentrating, while iron overload can damage the liver, heart, and other organs over time if not managed.
Statements made in the Clinical Manual have not been evaluated by the FDA. The products mentioned are not intended to diagnose, treat, cure or prevent any disease.
