Section Editors: Christopher McCudden Ph.D., DABCC, FADLM, FCACB and Kamran Mirza MD PhD
May 23, 2026
Blood tests are among the most commonly performed medical tests. They screen for disease, monitor known conditions, track treatment progress, and check organ function. The results can include dozens of individual measurements, and most patients receive their report with little or no explanation of what each number means.
This section provides plain-language guides to the most common blood tests, grouped by the organ or body system the test tells you about. Within each group, guides to whole panels come first, followed by guides to the individual measurements in the panel. Each article explains what the test measures, why it is ordered, what typical results mean, and what may happen next.
If you are looking for a definition of a single laboratory term, visit our Pathology Dictionary. If you are looking for a guide to a specific cancer biomarker, visit our Biomarkers and Molecular Testing section. For blood and other tests used to detect infections, including COVID-19, HIV, hepatitis, and other viral, bacterial, fungal, and parasitic infections, visit our Testing for Infections section.
Important note about reference ranges
The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown in these articles. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal (or unexpectedly normal) result with your doctor.
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Understanding reference ranges and units on a laboratory report
A guide to reading the numbers on a laboratory report, including what a reference range is, why ranges differ between laboratories, why the same test can be reported in two different units, and what a flagged result does and does not mean.
General Blood Panels
These panels are ordered together and cover several organ systems at once, so they don’t belong to any single organ. The sections below explain the individual measurements, grouped by the organ each one reflects.
Understanding your basic metabolic panel (BMP)
A guide to the eight measurements on a basic metabolic panel, including sodium, potassium, chloride, bicarbonate, blood urea nitrogen, creatinine, glucose, and calcium.
You may find this helpful if your blood test report includes electrolytes, kidney function tests, or a fasting glucose result as part of a routine blood panel.
Understanding your comprehensive metabolic panel (CMP)
A guide to the comprehensive metabolic panel, which expands on the basic metabolic panel by adding albumin, total protein, and the liver enzymes ALP, ALT, and AST, along with bilirubin.
You may find this helpful if your blood test was ordered as a CMP or “chem 14” and includes both kidney- and liver-related measurements.
Blood and Bone Marrow
These tests count and describe the cells in your blood, and look at how your blood clots. The panel guides come first, followed by guides to the individual measurements they contain.
Understanding your complete blood count (CBC)
A guide to the most commonly ordered blood test, including red blood cell count, hemoglobin, hematocrit, white blood cell count, platelets, and the indices that describe red blood cell size and content.
You may find this helpful if your blood test report includes terms like RBC, HGB, HCT, MCV, MCH, MCHC, RDW, WBC, PLT, or MPV.
Understanding your white blood cell differential
A guide to the breakdown of white blood cell types in your blood, including neutrophils, lymphocytes, monocytes, eosinophils, and basophils, and what high or low counts of each can mean.
This may be helpful if your report includes a differential count, an absolute neutrophil count (ANC), or terms like neutrophilia, lymphocytosis, or eosinophilia.
Understanding your peripheral blood smear
A guide to the peripheral blood smear, a test in which blood is examined under a microscope to identify abnormalities in the size, shape, and appearance of red blood cells, white blood cells, and platelets.
You may find this helpful if your blood test report includes findings from a peripheral blood smear, or your doctor ordered the smear after an unusual CBC result.
Understanding your coagulation panel
A guide to blood clotting tests, including prothrombin time (PT), international normalized ratio (INR), and partial thromboplastin time (PTT), and how these tests are used to monitor blood thinners and assess bleeding risk.
You may find this helpful if your report includes PT, INR, or PTT results, or if you are taking warfarin or another anticoagulant.
Understanding your hemoglobin disorder tests
A guide to the blood tests used to detect inherited hemoglobin disorders such as sickle cell disease and thalassemia, including hemoglobin electrophoresis, high-performance liquid chromatography (HPLC), hemoglobin solubility testing, and the sodium metabisulfite test.
You may find this helpful if you have been screened for sickle cell disease or thalassemia, or if your blood test report includes hemoglobin variant analysis.
A guide to the hematocrit result, including what share of your blood is made up of red blood cells, and why the value moves with hydration as well as with the number of cells.
You may find this helpful if your report shows HCT or hematocrit, or you were told you are anemic.
A guide to the MCV result, including why the average size of your red blood cells narrows down the possible causes of anemia before any other test is ordered.
You may find this helpful if your report shows MCV, or uses the words microcytic or macrocytic.
A guide to the two hemoglobin content measurements reported with every complete blood count, including why a high MCHC is nearly always a problem with the sample rather than a medical finding.
You may find this helpful if your report shows MCH or MCHC, or if one of them was the only flagged value on your complete blood count.
Red cell distribution width (RDW)
A guide to the RDW result, including what it means when red blood cells vary more than usual in size, and why RDW often changes before MCV does.
You may find this helpful if your report shows RDW, or RDW was flagged while the rest of your complete blood count was normal.
A guide to the monocyte result, including the difference between the monocyte percentage and the absolute monocyte count, why the absolute count is the one that matters, and why a mildly high count most often follows a recent infection.
A guide to the MPV result, including what the average size of your platelets reflects, how MPV is read alongside the platelet count, and why it is rarely acted on by itself.
Kidneys and Electrolytes
These tests show how well your kidneys filter your blood and measure the salts and minerals the kidneys help keep in balance.
Understanding your kidney function tests
A guide to the blood tests used to assess kidney function, including creatinine, blood urea nitrogen (BUN), estimated glomerular filtration rate (eGFR), cystatin C, and creatinine clearance.
You may find this helpful if your blood test report includes an eGFR, a creatinine result, or your doctor discussed your kidney function based on your blood test.
A guide to the creatinine result, including what creatinine is, how it is used to assess kidney function, and why an eGFR usually appears beside it on the same report.
You may find this helpful if your report shows a creatinine or eGFR result, or your doctor discussed your kidney function.
A guide to the urea result, including why urea is read against creatinine rather than on its own, and what the BUN-to-creatinine ratio can suggest about dehydration and kidney function.
You may find this helpful if your report shows urea, BUN, or a BUN-to-creatinine ratio.
A guide to the sodium result, including why a low sodium level is usually a sign of too much water in the body rather than too little salt in the diet.
You may find this helpful if your report shows sodium or Na, or you were told your sodium was low or that you have hyponatremia.
A guide to the potassium result, including what high and low levels can mean, and why a difficult blood draw can produce a falsely high result that needs repeating.
You may find this helpful if your report shows potassium or K, you were told your potassium was high (hyperkalemia), or you were asked to repeat the test.
A guide to the chloride result, including why chloride is rarely meaningful on its own and why the pattern it forms with sodium and bicarbonate is what your doctor reads.
You may find this helpful if your report shows chloride or Cl as part of an electrolyte panel.
Liver and Bile Ducts
These tests look for signs of liver injury and check how well the liver and the bile ducts are working. Liver enzymes and bilirubin also appear on a comprehensive metabolic panel, which is covered under General Blood Panels above.
Understanding your liver panel
A guide to liver function and liver injury tests, including ALT, AST, ALP, GGT, LDH, bilirubin, albumin, total protein, and prothrombin time, and what their patterns of elevation can suggest.
You may find this helpful if your blood test report includes liver enzymes, abnormal bilirubin, or a flagged ALT or AST result.
A guide to the bilirubin result, including the difference between total, direct, and indirect bilirubin, and what a raised level can mean for the liver, the bile ducts, and the red blood cells.
A guide to the albumin result, including what this protein does, why the level falls in liver disease, kidney disease, and prolonged illness, and how it is read beside total protein.
Alkaline phosphatase (ALP) (coming soon)
A guide to the ALP result, including why this enzyme comes from both the liver and the bones, and what tests are used to work out which of the two a raised level is coming from.
Gamma-glutamyl transferase (GGT) (coming soon)
A guide to the GGT result, including why it is often ordered to confirm that a raised alkaline phosphatase is coming from the liver, and what can raise it apart from liver disease.
Heart and Blood Vessels
These tests look for damage to the heart muscle and measure the fats in your blood that affect your arteries’ health.
Understanding cardiac biomarkers in your blood test
A guide to the blood tests used to detect heart muscle damage and heart failure, including troponin, BNP, NT-proBNP, creatine kinase (CK), and CK-MB.
You may find this helpful if you had a blood test for chest pain, a suspected heart attack, or to monitor heart failure.
Understanding your lipid panel
A guide to cholesterol and triglyceride testing, including total cholesterol, LDL, HDL, non-HDL cholesterol, and triglycerides, with explanations of what each measurement reflects about cardiovascular risk.
You may find this helpful if your blood test report includes a cholesterol panel or your doctor discussed cardiovascular risk based on your blood results.
LDL cholesterol (coming soon)
A guide to the LDL cholesterol result, including why it is the number most closely tied to cardiovascular risk, how it is usually calculated rather than measured, and why target levels differ from person to person.
HDL cholesterol (coming soon)
A guide to the HDL cholesterol result, including why a higher value is generally read as favorable, and why HDL is interpreted as part of the whole lipid panel rather than on its own.
Triglycerides (coming soon)
A guide to the triglyceride result, including how strongly it is affected by what you ate and drank before the test, and at what level it becomes a concern in its own right.
Thyroid Gland
These tests measure thyroid hormones and the pituitary hormone that controls them.
Understanding your thyroid function tests
A guide to thyroid blood testing, including TSH, free T3, free T4, and thyroid antibodies, and what abnormal results may suggest about thyroid function and autoimmune thyroid disease.
You may find this helpful if your blood test report includes a TSH result, your doctor mentioned hypothyroidism or hyperthyroidism, or you have been screened for thyroid antibodies.
TSH (coming soon)
A guide to the TSH result, including why a test of a pituitary hormone is the first test of thyroid function, and why TSH moves in the opposite direction to the thyroid hormones themselves.
Free T4 (coming soon)
A guide to the free T4 result, including what the unbound portion of thyroid hormone measures, and why it is ordered when TSH is abnormal or when TSH alone does not fit the clinical picture.
Other Hormone-Producing Glands
These tests measure hormones made by the adrenal glands, parathyroid glands, ovaries, and testicles.
Understanding your adrenal hormone tests
A guide to blood tests of the adrenal glands, including cortisol, adrenocorticotropic hormone (ACTH), and aldosterone, and what abnormal results may suggest about adrenal function.
You may find this helpful if your blood test report includes cortisol or ACTH results, or your doctor mentioned Addison’s disease, Cushing’s syndrome, or adrenal insufficiency.
Understanding your parathyroid hormone (PTH) and calcium balance tests
A guide to the blood tests used to assess calcium balance, including parathyroid hormone (PTH), ionized calcium, phosphorus, and vitamin D.
You may find this helpful if your blood test report includes a PTH or vitamin D result, your calcium level was abnormal, or your doctor discussed bone health, kidney stones, or parathyroid disease.
Understanding your reproductive hormone panel
A guide to the blood tests used to assess fertility and reproductive health, including follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol, progesterone, testosterone, free testosterone, sex hormone-binding globulin (SHBG), anti-Mullerian hormone (AMH), and prolactin.
You may find this helpful if your blood test report includes hormone results, you are being investigated for infertility or menstrual irregularities, or you are receiving gender-affirming care.
Blood Sugar and Diabetes
These tests measure blood sugar and are used to diagnose and monitor diabetes.
Understanding your hemoglobin A1c (HbA1c) result
A guide to the HbA1c test, which measures average blood glucose over the past two to three months and is used to diagnose and monitor diabetes.
You may find this helpful if your blood test report includes an HbA1c result, your doctor diagnosed prediabetes or diabetes, or you are using A1c to track your blood sugar control over time.
Understanding your fasting glucose and oral glucose tolerance test (OGTT)
A guide to the fasting plasma glucose test and the oral glucose tolerance test, two of the most common blood tests used to detect diabetes and gestational diabetes.
You may find this helpful if you have had a fasting blood sugar test or a glucose tolerance test during pregnancy or for diabetes screening.
Iron, Vitamins, and Nutrition
These tests measure how much iron and certain vitamins your body has stored.
A guide to the blood tests used to assess iron levels and storage, including serum iron, ferritin, transferrin, total iron-binding capacity (TIBC), and transferrin saturation.
You may find this helpful if your blood test report includes a ferritin result, your doctor mentioned iron deficiency or iron overload, or you have been investigated for anemia.
Ferritin (coming soon)
A guide to the ferritin result, including why it is the best single measure of iron stores, and why it also rises with inflammation, which can hide iron deficiency.
Vitamin B12 (coming soon)
A guide to the vitamin B12 result, including what a low level can mean for the blood and the nervous system, and what further tests are used when the result is borderline.
Immune System and Inflammation
These tests measure inflammation in the body and look for antibodies the immune system makes against your own tissue.
Understanding your inflammatory markers
A guide to blood tests that measure inflammation in the body, including C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and ferritin as a marker of inflammation.
You may find this helpful if your blood test report includes CRP or ESR results, or if your doctor discussed inflammation in the context of an autoimmune or infectious condition.
Understanding your autoimmune panel
A guide to the blood tests used to detect autoimmune diseases, including antinuclear antibody (ANA), anti-double-stranded DNA, rheumatoid factor, anti-CCP, anti-tissue transglutaminase, anti-LKM-1, and smooth muscle antibody (SMA).
You may find this helpful if your blood test report includes autoimmune antibody results, or your doctor is investigating lupus, rheumatoid arthritis, autoimmune hepatitis, or another autoimmune condition.
Understanding your celiac disease testing
A guide to the blood tests used to screen for and help diagnose celiac disease, including anti-tissue transglutaminase IgA (anti-TTG IgA), anti-endomysial antibodies, deamidated gliadin peptide antibodies, and total IgA.
You may find this helpful if your blood test report includes celiac antibody results, or you are being investigated for unexplained gastrointestinal symptoms, anemia, or nutrient deficiencies.
Blood Tests Used in Cancer Care
These tests help detect cancer or monitor cancer after it has been diagnosed.
Understanding tumor markers in your blood test
A comprehensive guide to the blood tests used to detect or monitor cancer, including PSA (prostate), AFP (liver and germ cell), CEA (colorectal and others), CA 19-9 (pancreas), CA 125 (ovary), CA 15-3 and CA 27-29 (breast), beta-HCG (germ cell and gestational), calcitonin (medullary thyroid), and thyroglobulin (thyroid).
You may find this helpful if your blood test report includes a tumor marker result, your doctor is using a tumor marker to monitor a known cancer, or you are being screened for a specific type of cancer.
Understanding your prostate-specific antigen (PSA) result
A guide to the PSA test, including how it is used for prostate cancer screening and monitoring, what factors can raise PSA levels, and how PSA is interpreted in the context of prostate biopsy results and active surveillance.
You may find this helpful if your blood test includes a PSA result, you are being screened for prostate cancer, or you are following PSA results during or after treatment.
Blood Tests Before Starting a Medication
These inherited genetic tests predict how your body will break down certain medications, so the dose can be adjusted before treatment starts.
Understanding your TPMT and NUDT15 test results
A guide to the inherited genetic test that predicts how your body breaks down thiopurine medications, including azathioprine, mercaptopurine (6-MP), and thioguanine, and what normal, intermediate, and poor metabolizer results mean for dosing.
You may find this helpful if your report includes a TPMT or NUDT15 result, or you are starting a thiopurine medication for inflammatory bowel disease, an autoimmune condition, a transplant, or leukemia.
Understanding your DPYD test result
A guide to the inherited genetic test that predicts how your body breaks down fluoropyrimidine chemotherapy, including 5-fluorouracil (5-FU) and capecitabine, and what normal, intermediate, and poor metabolizer results and the activity score mean for dosing.
You may find this helpful if your report includes a DPYD result or activity score, or you are starting 5-FU or capecitabine (Xeloda) for a cancer such as colorectal, breast, stomach, or pancreatic cancer.
Blood Tests Before a Transfusion or Transplant
These tests match your blood or tissue type with a donor’s before a transfusion or organ transplant.
Understanding your blood typing and compatibility tests
A guide to the blood tests used before a transfusion or pregnancy, including ABO blood typing, Rh factor testing, antibody screening, and crossmatching.
You may find this helpful if you had blood typing before surgery or a transfusion, you are pregnant, and your blood was tested for Rh status, or you have received a transfusion reaction workup.
Understanding your transplant compatibility tests
A guide to the blood tests used to match donors and recipients before organ transplantation, including human leukocyte antigen (HLA) typing, donor-specific antibodies (DSA), and panel reactive antibodies (PRA).
You may find this helpful if you are awaiting an organ transplant or have received one, and your reports include HLA typing, DSA testing, or PRA results.
Don’t see your blood test listed?We add neww blood test guides regularly. In the meantime, our Pathology Dictionary defines many laboratory test terms, and Osler, our pathology chatbot, can help explain specific results from your report in plain language.
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