Acute phase proteins are molecules in the blood that either increase or decrease in response to tissue injury including trauma, heart attack, infections, burns, chronic inflammation (like rheumatoid arthritis), and cancer.
When the body is injured, immune cells flood to the area to help the body heal and/or fight off harmful substances (such as bacteria or viruses). This increase in immune cells leads to inflammation in the body.
Acute phase proteins help the body respond to tissue injury. For instance, some proteins may help cells destroy harmful substances, such as bacteria, while others may help the blood clot and prevent blood loss. When acute phase proteins respond to tissue injury, this is called an acute phase reaction.
It remains unknown exactly how the acute phase proteins are stimulated. However, research suggests that the chemicals released during injury may activate the proteins.
Among the most common acute phase proteins are ceruloplasmin, C-reactive protein (CRP), fibrinogen, ferritin, haptoglobin, serum albumins, serums amyloid A, and transferrin. These proteins are continually produced in the liver.
Abnormal levels of acute phase proteins in the blood may indicate tissue injury or infection. They may also indicate long-term immune system disorders. For instance, blood tests that measure the levels of acute phase proteins are often used to diagnose and monitor conditions like inflammatory disorders (such as arthritis), cancer, and autoimmune disorders (such as lupus). Autoimmune disorders occur when the body's immune system mistakenly attacks body cells because they are perceived as harmful invaders.
Ceruloplasmin, also called ferroxidase, is a copper-containing blood protein. This protein removes iron from cells, preventing iron deposits from building up in the body. If iron collects inside the body's cells, it may lead to tissue damage and disease. Ceruloplasmin increases in response to inflammation.
Healthy males typically have 16.2-35.6 milligrams of ceruloplasmin per deciliter of blood, and healthy females typically have 17.9-53.3 milligrams of ceruloplasmin per deciliter of blood. Elevated levels may indicate pregnancy, lymphoma (a type of cancer), and/or inflammation. Decreased levels may indicate Menke's disease (rare disorder that causes sparse and coarse hair and nervous system deterioration), Wilson's disease (inherited disorder that causes copper to build up in the body tissues), overdose of vitamin C, or copper deficiency.
C-reactive protein (CRP) increases in response to tissue injury. It has been suggested that CRP helps immune cells destroy foreign substances, such as bacteria and viruses, which enter the body. Scientists believe that CRP helps white blood cells attach to foreign invaders, triggering other cells to destroy the invading substance.
While the test is not specific enough to diagnose a particular disease, it can be used to help physicians monitor inflammation and determine if current treatments are effective.
Healthy individuals typically have less than 10 milligrams of CRP per liter of blood. A high or increasing amount of CRP in the blood suggests that the patient has a serious infection or inflammation. CRP levels can increase up to 1,000-times when inflammation occurs. High levels of CRP are associated with inflammatory disorders, such as rheumatoid arthritis. Recent research suggests that high levels of CRP may also indicate an increased risk of heart attack. However, researchers are still investigating this relationship to further understand the role of CRP.
Fibrinogen is a blood protein that is produced in response to tissue injury. This protein is a coagulation factor because it helps blood clot and reduces bleeding. Healthy individuals have 200-400 milligrams of fibrinogen per deciliter of blood.
Erythrocyte sedimentation rate (ESR) test: During an inflammatory response, the high proportion of fibrinogen in the blood causes red blood cells to stick together. The red blood cells form stacks called rouleaux, which settle faster than normal. The time it takes for red blood cells to settle can be determined by testing erythrocyte sedimentation rate (ESR). Elevated levels usually occur in patients who have autoimmune disorders.
An ESR test may be conducted to measure and monitor inflammation. While an ESR test is not diagnostic, it is useful in detecting and monitoring tissue necrosis (death), long-term inflammatory conditions (such as rheumatoid arthritis), and other diseases that present vague and minimal physical symptoms.
Normal values for men younger than 50 years old are 15 millimeters per hour and normal values for men older than 50 are less than 20 millimeters per hour. The normal values for women who are less than 50 years old are less than 20 millimeters per hour, and normal values for women older than 50 are less than 30 millimeters per hour.
Fibrinogen test: During a fibrinogen blood test, a small sample of blood is taken from the patient in order to measure the amount of fibrinogen in the blood. Healthy individuals typically have 200-400 milligrams of fibrinogen per deciliter of blood. Increased levels of fibrinogen may indicate infection, coronary heart disease (CAD), inflammatory disorders, heart attack, stroke, trauma, disseminated intravascular coagulation (DIC), or breast, kidney, or stomach cancer.
Ferritin is a protein found inside the cells that store iron so that the body can use it later. During injury, ferritin releases iron so that the body can produce a protein called hemoglobin. The red blood cells then use this hemoglobin to carry oxygen to the body. Ferritin is present in most tissues, especially the bone marrow.
A minority of the body's ferritin is present in the blood. The ferritin blood test indicates how much iron is stored in the body for future use. Healthy males typically have 12-300 nanograms of ferritin per milliliter of blood, while healthy females typically have 12-150 nanograms of ferritin per milliliter of blood. Elevated levels may indicate an inflammatory condition, cancer, or liver disease. Decreased levels may indicate anemia, a condition where there are low levels of iron in the blood.
Haptoglobin is a protein that increases in response to tissue damage, which may be caused by inflammation, cancer, surgery, or trauma. This is because an increased number of red blood cells die during tissue damage. When red cells die, they release a protein called hemoglobin that carries oxygen. Haptoglobin attaches to hemoglobin in the blood. Therefore, the more hemoglobin in the blood, the more haptoglobin is produced.
A haptoglobin blood test may be performed to determine how fast the blood cells are destroyed. Healthy individuals have 27-139 milligrams per deciliter of blood. Increased levels of haptoglobin may indicate rheumatic disease, peptic ulcer, ulcerative colitis, or other inflammatory conditions. Decreased levels of haptoglobin may indicate conditions, such as chronic liver disease, hematoma (blood clot), anemia, or liver disease.
Serum albumin proteins, which are the most abundant proteins in the clear, fluid portion of blood (serum), typically decrease during inflammation. Albumin helps the body tissues maintain the pressure necessary for proper distribution of body fluids. If the pressure inside and outside of body tissues is not equal, it can potentially lead to tissue damage. Healthy individuals typically have 3.4-5.4 grams of albumin per deciliter of serum.
The serum albumin blood test measures the levels of albumins in the serum. Increased levels may indicate diabetic nephropathy, degenerative liver disease, combined liver and kidney failure, kidney disease or Wilson's disease. Decreased levels may indicate fluid in the abdomen, extensive burns, liver disease (such as hepatitis or cirrhosis), poor absorption syndrome (such as Crohn's disease), malnutrition, or nephrotic syndrome (high levels of protein in the urine, indicating kidney damage).
Serum amyloid A (SAA) is a protein that is released during inflammation that stimulates other immune cells to travel towards the site of injury.
Healthy individuals generally have 1.57-2.73 milligrams of SAA per liter of serum (clear, fluid portion of blood). Increased levels of SAA are associated with several inflammatory conditions, including amyloidosis (buildup of proteins in the tissues), atherosclerosis (clogging and narrowing of the arteries), and rheumatoid arthritis.
Transferrin is a blood protein that transports iron in the bloodstream to the red blood cells. Transferrin typically decreases in response to an inflammatory condition. Healthy individuals have 60-170 micrograms per deciliter of serum.
The total iron-binding capacity (TIBC) and transferrin test measures how much iron is carried in the blood. Individuals who have low iron with a high transferrin or TIBC usually have iron deficiency (anemia). Healthy individuals typically have TIBC values of 240-450 micrograms per deciliter of serum.
The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.