Several features of the blood are measured in the complete blood count.

The Red blood cell evaluates

Red Blood Cell Count: Red blood cells (RBCs), also called erythrocytes, are cells that carry oxygen from your lungs to the rest of your body. The RBC counts the number of red blood cells that are present in your blood sample. If your RBC count is too low, you may have anemia or another condition.
Hemoglobin: It is the oxygen-carrying protein in red blood cells that gives the cells their representative red color.
Hematocrit:  It measures the volume percentage of RBC (Red Blood Cells) in the blood. A hematocrit value of 30% means that there are 30 milliliters of RBC in 100 milliliters of whole blood. 
The CBC blood test also provides important information on various red blood indices including

Mean corpuscular volume (MCV) is a measurement of the average size of red blood cells.
Mean corpuscular hemoglobin (MCH) is a calculated measurement of the average amount of hemoglobin inside red blood cells.
Mean corpuscular hemoglobin concentration (MCHC) is a calculated measurement of the average concentration of hemoglobin inside red blood cells.
Red cell distribution width (RDW) is a measurement of the variation in the size of red blood cells.

White blood cell tests

White blood cells (WBC) count:  It defines the total number of white blood cells in your blood sample. WBC helps your body fight against infection. A CBC measures the number and five types of white blood cells present (neutrophils, lymphocytes, monocytes, eosinophils, and basophils). 

Platelet tests

Platelets(thrombocytes) assist in blood clotting. The platelet count is a test that measures the number of platelets in your blood sample.
Mean platelet volume (MPV) is a measurement of the average size of platelets.

The CBC blood test is a great indicator of overall health and detects a variety of diseases and conditions, such as infections, anemia, and leukemia. Any increase or decrease in cell counts can indicate an underlying medical problem. It can give you and your health provider a heads up that further investigation is required. A CBC is also done to keep track of an existing medical condition or treatment. 

A CMP blood test measures 14 different substances in your blood and provides significant information about your body's chemical balance and metabolism. The CMP is usually ordered as part of a routine checkup or when you are being monitored for a specific condition like hypertension or diabetes or are taking medications that may affect your kidney or liver.

A CMP includes tests for the following:

Glucose is the main energy source for the body's cells and a relatively steady amount of glucose is a must in the body. Glucose monitoring is usually done to detect diabetes.

Calcium is an important mineral and is required for the proper functioning of nerves, muscles, and heart.

Protein tests

Protein tests including Albumin, Total Protein, Albumin/Globulin Ratio are used to measure the number of proteins in the blood as they are imperative building blocks of all cells and tissues and are crucial for the overall growth and development of the body.

Electrolytes

Electrolytes are minerals that help the transportation of nutrients into the body's cells and assist in removing wastes out of the cells. Sodium, potassium, carbon dioxide, and chloride are electrolytes, which help regulate the body's fluid levels and its acid-base (pH) balance.

Kidney Tests

BUN/Creatinine Ratio, Creatinine with GFR, and Urea Nitrogen tests are required to assess kidney function.

Liver Tests

ALP (alkaline phosphatase), ALT (alanine transaminase), and AST (aspartate aminotransferase) are different enzymes made by the liver and part of the CMP panel.
Bilirubin is a waste product produced by the normal breakdown of red blood cells. This is used to evaluate a person's liver function or to screen for or monitor liver disorders.

The Hemoglobin A1c also called A1c or glycated hemoglobin is hemoglobin with glucose attached. The test is recommended by the American Diabetes Association in the assessment of blood glucose levels to determine diabetes risk. It is recommended that A1c testing should be performed routinely in all patients with diabetes. The A1c test reflects the average blood sugar over the past two to three months. Therefore, doctors advise taking the test at least twice a year and more frequently in some cases (1, 2).

Lipids are a collection of fats and fat-like substances that are considered an important component of cells and sources of energy. The Lipid Panel blood test measures the essential lipids of the blood for monitoring. This tests the triglyceride and serum cholesterol levels. Since it aids in the evaluation of possible cardiovascular risk, this test includes evaluation of the High-density lipoprotein cholesterol (HDL-C, often termed as “good cholesterol”), HDL-C ratio, Low-density lipoprotein cholesterol (LDL-C, often termed as “bad cholesterol”), Non-HDL-C (calculated from total cholesterol minus HDL-C), and total cholesterol (evaluates all the cholesterol in all the lipoprotein particles).

Maintaining normal levels of these lipids is thus essential in leading a healthy life. Cholesterol is needed for the body but eating too much of foods that are high in saturated fats and trans unsaturated fats can result in a high level of cholesterol in the blood, which is actually not needed and bad for the body. The extra and unwanted cholesterol may be dumped as plaques on the walls of blood vessels and heightens the risk of numerous health issues, including heart disease and stroke. The Lipid Panel blood test thus helps in detecting cardiovascular risk. Additionally, it also helps identify if the patient is suffering from an ischemic event and may be used in the prevention and management of atherosclerotic disease, as well as in the detection of metabolic syndrome.

It is important to understand that the high levels of HDL (good cholesterol) are associated with a reduced risk of heart and blood vessel disease, whereas high levels of LDL (bad cholesterol) are associated with increased risk of heart and blood vessel disease, including coronary artery disease and heart attacks.

Magnesium is an important mineral in the body that helps maintain the health of the nerves, muscles, heart, and bones. It also helps control blood sugar and blood pressure and manages your energy levels. The magnesium blood test is used to measure blood magnesium levels.

Magnesium deficiency is usually observed in malnutrition, malabsorption states, and kidney disease. High magnesium levels can be caused by excessive antacid intake and decreased ability of the kidneys to excrete the mineral. Magnesium imbalance can lead to signs and symptoms such as nausea, loss of appetite, weakness, irritability, muscle cramps, numbness, tingling, or irregular heart rate (Cardiac arrhythmia). Magnesium imbalance in the body can also affect calcium metabolism and aggravate calcium deficiencies.

Testosterone is the primary sex hormone in men that is responsible for the development of male sexual characteristics. It is produced in the Leydig cells of the male testicles. It is also secreted by the adrenals in both males and females; however in minimal amounts by the ovaries in females. In women, testosterone is converted to estradiol which is considered the main sex hormone in females.

The testosterone blood test is used to measure the testosterone levels in the blood.  This test is performed to diagnose various reproductive health problems such as erectile dysfunction, low sex drive, and infertility in men; and virilization or polycystic ovary syndrome in women. This test also helps in determining the cause of ambiguous genitalia.

TSH is created by the pituitary gland, and that can be located at the base of the brain. The gland is used to regulate thyroid hormones. You can find the thyroid at the front of the neck and is butterfly shaped. The thyroid produces three main hormones - triiodothyronine (T3), thyroxine (T4) and calcitonin. Metabolism and growth are just some of the functions controlled by the thyroid. The thyroid gland and pituitary gland work together to make sure the right about of thyroid hormones are produced. When this system is disrupted it can play havoc on the body. A TSH can show how well the thyroid is working.

Uric acid is a substance that results from the breakdown of purines, which are nitrous compounds found in the body, such as in the DNA of cells. With time, cells age and breakdown, resulting in the release of purines into the blood. Not generally but to a lesser extent, purines may come from ingesting foods like beans, legumes, liver, and anchovies. It can also come from excessive alcohol intake. 

Uric acid is mostly removed from the body with the help of kidneys via urine, with the remainder removed in the stool. However, if the body is producing too much uric acid or enough is not removed by the kidneys, it could lead to many health issues including gout (inflammation of the joints), kidney stones, or more severe, kidney failure.

The uric acid blood test is used to detect high levels of uric acid in the blood. It is often used to monitor uric acid levels in those undergoing chemotherapy or radiation care. It also helps determine your risk for kidney stones and helps monitor developing gout.

Folic acid deficiency is common in pregnant women, alcoholics, patients with diets that do not include raw fruits and vegetables, and people with structural damage to the small intestine. The most reliable and direct method of diagnosing folate deficiency is the determination of folate levels in both erythrocytes and serum. Low folic acid levels, however, can also be the result of a primary Vitamin B12 deficiency that decreases the ability of cells to take up folic acid. Vitamin B12 is decreased in pernicious anemia, total or partial gastrectomy, malabsorption and certain congenital biochemical disorders.

Vitamin D is a fat-soluble vitamin that helps regulate calcium and phosphate in the body and keeps bones, muscles, and teeth healthy. Its deficiency can lead to bone problems like osteomalacia, softening of a person’s bones.

There are two forms of vitamin D present in the blood: 25-hydroxyvitamin D and 1,25-dihydroxy vitamin D. Of these two, 25-hydroxyvitamin D is the major form found in the blood and is commonly measured to evaluate and monitor vitamin D status in individuals.

The Vitamin D, 25 Hydroxy Blood Test is used to monitor vitamin D levels in the body. This test helps determine whether a person is at risk for developing bone problems such as rickets, bone malformations, bone weakness, or osteoporosis. Generally, this test is used to diagnose vitamin D deficiency and Hypervitaminosis D. It can also be used for monitoring Vitamin D replacement therapy.

Triiodothyronine, Free T3, is not affected by certain protein levels causing them to remain more constant. This test will therefore assess abnormal binding protein disorders. Triiodothyronine (T3) is a thyroid hormone that plays a role in nearly every physiological process in the body. It plays a key role in development, growth, the regulating of heart rate, metabolism and the body's temperature. Possible thyroid issues can be hyperthyroidism, hypopituitarism, primary or secondary hypothyroidism and thyrotoxic periodic paralysis. A thyroid disorder can create symptoms of anxiety to constipation.

The hs-CRP blood test is used to diagnose your risk for inflammation and cardiovascular disease. C-reactive protein (CRP) is an acute-phase protein released in the blood during inflammation. As this protein is a marker of inflammation, it is elevated in the blood when there are inflammatory conditions, cancer, infections, or even heart disease present. One should not confuse the standard CRP test with the hs-CRP test. hs-CRP test more precisely detects the lower levels of the protein than that measured by the standard CRP test. A high-sensitivity C-reactive protein (hs-CRP) test, can also be used to assess your risk of developing coronary artery disease, a disorder in which the blood arteries of your heart are narrowed. Coronary artery disease can become a reason for a heart attack.

Most of the T4 in your body is bonded to protein, and a smaller portion (free) has not. This is why there is a free T4 test and a total T4 test. A free T4 test is usually preferred because from this test you can see how much is available for the body to use. This test can be ordered if a TSH has come back abnormal. Pregnancy can also affect your T4 levels.

The test is used to measure total iron, iron-binding capacity, percent saturation (calculated), and ferritin levels in the blood. The Iron test checks the iron levels in the blood. The total iron-binding capacity (TIBC) test examines if you have too much or too little iron in your blood. Iron moves through the blood attached to a protein called transferrin and the TIBC test is a good indirect measurement of transferrin availability. Ferritin testing measures the iron storage capacity in the body and if it happens to be on the lower side, it is an indicator of iron deficiency. Overall, the test is used to assess how the body transports iron in the blood, and to investigate iron-deficiency anemia or iron overload.