Blood work gives a detailed snapshot of what’s happening inside your body, from how well your organs are functioning to whether you’re fighting an infection or running low on key nutrients. A standard set of blood tests can check your blood cell counts, blood sugar, cholesterol, liver and kidney health, thyroid function, and inflammation levels. Most routine results come back within hours to a few days, while specialized tests sent to reference labs can take a week or more.
Complete Blood Count
The complete blood count, or CBC, is one of the most commonly ordered blood tests. It measures three major types of blood cells: red blood cells, white blood cells, and platelets. Red blood cells carry oxygen from your lungs to the rest of your body. White blood cells fight infections and disease. Platelets help your blood clot to stop bleeding.
A CBC also measures hemoglobin, the iron-rich protein inside red blood cells that actually binds to oxygen, and hematocrit, which tells you what percentage of your blood is made up of red blood cells. Low hemoglobin or hematocrit can signal anemia. The test also reports the average size of your red blood cells, which helps narrow down the cause of anemia if one is found.
A version called a CBC with differential breaks your white blood cells into five subtypes. Each type responds to different threats, so the breakdown can help distinguish between a bacterial infection, a viral illness, allergies, or more serious blood disorders. A high overall white blood cell count often points to infection or inflammation, while a low count may indicate an immune system problem.
Blood Sugar and Diabetes Screening
Blood work measures glucose, your body’s main energy source. A fasting glucose test captures your blood sugar level after you haven’t eaten, giving a baseline reading. Consistently elevated fasting glucose suggests your body is struggling to regulate blood sugar, which can indicate prediabetes or diabetes.
The A1C test provides a broader picture. Rather than a single moment in time, it reflects your average blood sugar over the past two to three months. The CDC uses these ranges for diagnosis: below 5.7% is normal, 5.7% to 6.4% is prediabetes, and 6.5% or above is diabetes. This test doesn’t require fasting, which makes it convenient for routine screening.
Liver and Kidney Function
A comprehensive metabolic panel, or CMP, checks how well your liver and kidneys are working. For the liver, it measures three key enzymes: ALP, ALT, and AST. These enzymes are mainly produced in the liver and help drive chemical reactions throughout your body. When liver cells are damaged or inflamed, they release higher amounts of these enzymes into your bloodstream. Elevated levels can result from anything from medication side effects to fatty liver disease to hepatitis.
For the kidneys, the panel measures two waste products: blood urea nitrogen (BUN) and creatinine. Your kidneys filter both of these out of your blood and remove them through urine. When kidney function declines, these waste products build up, so rising levels on a blood test can be an early warning sign of kidney disease before you notice any symptoms.
Cholesterol and Heart Health
A lipid panel measures the fats circulating in your blood and is a primary tool for assessing cardiovascular risk. It reports four main numbers:
- Total cholesterol: the combined measure of all cholesterol in your blood. For adults 20 and older, less than 200 mg/dL is considered healthy.
- LDL cholesterol: often called “bad” cholesterol because it builds up in artery walls and can form blockages. Healthy is below 100 mg/dL.
- HDL cholesterol: often called “good” cholesterol because it helps remove cholesterol from your arteries. Levels of 60 mg/dL or higher are ideal. Below 40 mg/dL for men or 50 mg/dL for women is considered low.
- Triglycerides: another type of blood fat that raises heart disease risk. Normal is below 150 mg/dL, borderline high is 150 to 199 mg/dL, and high is 200 mg/dL or above.
These numbers are typically evaluated together rather than individually. Someone with borderline LDL but very high triglycerides and low HDL may still have significant cardiovascular risk.
Inflammation Markers
Your liver produces a protein called C-reactive protein (CRP) whenever there’s inflammation in your body. A CRP blood test measures how much of this protein is circulating. Healthy people typically have very low levels, around 0.8 to 1.0 mg/dL or lower. Any increase above that range suggests inflammation somewhere in your body.
CRP rises in response to both acute and chronic conditions, including bacterial and viral infections, autoimmune diseases, and chronic inflammatory conditions. It’s also useful for tracking treatment. If your CRP levels fall over time, it’s a sign that whatever is causing the inflammation is improving. Because CRP responds to inflammation broadly rather than pointing to a specific cause, it’s usually combined with other tests to narrow down the diagnosis.
Thyroid Function
Thyroid blood tests check whether your thyroid gland is producing the right amount of hormones. The first test most providers order is TSH, or thyroid-stimulating hormone. Your brain’s pituitary gland produces TSH to tell your thyroid how much hormone to make. High TSH typically means your thyroid is underactive (hypothyroidism), because your brain is sending stronger signals trying to get the thyroid to produce more. Low TSH suggests the opposite: an overactive thyroid (hyperthyroidism) that’s already producing too much, so the brain dials back its signal.
If TSH comes back abnormal, follow-up tests measure the actual thyroid hormones: T3 (triiodothyronine) and T4 (thyroxine). Checking these alongside TSH gives a complete picture of how the thyroid is functioning and helps determine the cause and severity of the problem.
Nutritional Deficiencies
Blood work can reveal whether you’re low on essential vitamins and minerals. Vitamin D, vitamin B12, and iron are among the most frequently tested. Low vitamin D is extremely common and can affect bone health, energy, and immune function. Vitamin B12 deficiency can cause fatigue, nerve problems, and a specific type of anemia where red blood cells are abnormally large. Iron deficiency is the most common nutritional deficiency worldwide and leads to anemia, fatigue, and weakness.
Ferritin, a protein that stores iron, is often tested alongside iron levels because it gives a more accurate picture of your body’s iron reserves. You can have normal iron in your blood but low ferritin, meaning your stores are depleted and you’re headed toward deficiency. These nutritional tests are not always included in standard panels and usually need to be specifically requested.
Preparing for Blood Work
Some blood tests require fasting beforehand, typically for 8 to 12 hours. The tests that most commonly require fasting include blood glucose, lipid panels, and basic metabolic panels. Liver and kidney function tests sometimes require fasting as well. Your provider will specify the exact duration based on which tests are ordered. Water is generally fine during the fasting period.
Several everyday factors can affect the accuracy of your results. Eating or drinking certain foods, taking medications or supplements, exercising hard before the test, and even having a menstrual period can all shift values. Not following preparation instructions, especially fasting requirements, is one of the most common reasons for misleading results. If a value comes back slightly abnormal, your provider may simply retest before drawing any conclusions.
How Long Results Take
Routine blood panels like a CBC, metabolic panel, or lipid panel are processed frequently throughout the day at most labs, so results typically come back within hours to a couple of days. More specialized tests, such as certain hormone panels, autoimmune markers, or genetic testing, may be sent to a reference lab and take at least a week. Many labs and health systems now post results directly to an online patient portal, often before your provider has had a chance to review them. If you see a flagged result, keep in mind that a single out-of-range value doesn’t necessarily indicate a problem. Results are most meaningful when interpreted alongside your symptoms, medical history, and trends over time.