A variety of blood tests help us to assess liver injury or function. In assessing a patient, the blood work must be used in combination with the child's physical exam and clinical history to assess how good liver function really is.
Albumin is a small protein in the blood which helps fluid to stay within the bloodstream. Measurement of albumin tells us about "liver synthetic function", or how well the liver makes protein.
Bilirubin is a byproduct of the normal breakdown of red blood cells. Unconjugated bilirubin is processed or "conjugated" in the liver when excreted in the bile. Elevated conjugated bilirubin occurs when bile flow from the liver is blocked or when the liver is not working well.
Clotting studies or PT/PTT, or "coags" are used to measure blood clotting. These tests reflect the liver's ability to make the crucial proteins that allow the blood to clot. It is interesting to know that a deficiency in vitamin K can also make blood clotting abnormal, even when the liver works well. This is because the liver needs vitamin K to make some clotting factors.
There are several enzymes in the liver which help it perform its biochemical functions. The "transaminases" help process small pieces of protein called amino acids. The levels of ALT (also called SGPT) and AST (also called SGOT) can be measured in the blood. When the liver is injured, dead liver cells release these enzymes into the bloodstream. Where a normal patient might have an ALT of 40, a patient with an active hepatitis might have an ALT of a few hundred. A patient with a severe sudden injury to the liver with massive liver cell death might have an ALT of 10,000. These enzymes do not tell you how the liver works; they simply reflect injury to the liver. Two other enzymes, alkaline phosphatase and GGT (gamma glutamyltransferase) tend to reflect bile duct problems. This can be tricky, however, as alkaline phosphatase can sometimes be released by other tissues such as bone and lung. In many diseases of the bile duct, the alkaline phosphatase and gamma GT are elevated. In other diseases, both the transaminases and the alkaline phosphatase/gamma GT are elevated, reflecting injury to all types of liver cells.
Tests for Specific Liver Diseases
There are a variety of blood tests that assess for specific liver diseases. Below is a list of those tests.
Tests for Autoimmune Disease
- ANA (Antinuclear Antibody): Looks for an antibody (protein) that forms to the nuclei of cells. High results (>1:320) can signify that the patient has type I autoimmune hepatitis with immune cells inappropriately attacking the liver.
- Anti-SMA (Antismooth Muscle Antibody): Is a protein that forms against muscle. It is strongly positive in patients with type I autoimmune hepatitis.
- IgG: This immune protein or immunoglobulin is elevated in most patients with autoimmune hepatitis.
- Anti-LKM (Anti Liver-Kidney Microsomal Antibody): Is positive in type II autoimmune hepatitis, which tends to affect younger children. This antibody forms against parts of liver and kidney cells.
Tests for Metabolic Liver Disease
- Alpha-1 antitrypsin Level and Phenotype: Can test for the commn metabolic disease alpha-1 antitrypsin deficiency. An alpha-1 antitrypsin level simply shows how much of this protein is present in the bloodstream. This result will be low in alpha-1 antitrypsin deficiency disease. A more specific test is the alpha-1 antitrypsin phenotype. This actually shows the typing of the alpha-1 antitrypsin protein in the patient's bloodstream. A normal patient is MM. A patient with alpha-1 antitrypsin deficiency is ZZ. A carrier will be MZ. There is also a less common type called SZ where patients can behave as if they have alpha-1 antitrypsin deficiency. Genetic testing is available to confirm the presence of alpha-1 antitrypsin deficiency at the DNA level.
- Blood Carnitine Levels, Blood Acylcarnitine Levels or Urine Acylglycines: May be ordered if your child is suspected of having a metabolic disorder involving a part of cells called mitochondria. Abnormalities of these tests can lead doctors to order more sophisticated testing for mitochondrial disease.
- Ceruloplasmin and Copper Measurements: This blood test is used to screen for a metabolic disease called Wilson's disease, in which patient store copper in the liver. Ceruloplasmin is a copper-carrying protein and is decreased in patients with Wilson's disease. A 24-hour urine collection to quantitate copper may be another helpful test for diagnosing Wilson's disease. The most accurate test for diagnosing Wilson's is to do a liver biopsy and send the biopsy sample for a measurement of liver copper (which is high in patients with Wilson's).
- Ferritin Level: May also give an idea of iron overload in a disease called hemochromatosis. A more accurate test is done on a liver biopsy sample, where the amount of iron present in the sample is measured by the laboratory (this is called liver iron content). A genetic test for hematochromatosis called HHFE genotype is available.
- Iron and Total Iron Binding Capacity (Fe/TIBC): May be done to assess a patient for hemochromatosis, a condition in which iron accumulates in the liver and other tissues of the body.
- Lysosomal Enzyme Panel: May be ordered if your child is suspected of having a lysosomal storage disease. Lysosomes are small parts of cells that digest a variety of materials. If lysosomes lack a certain enzyme due to a metabolic disease, the material may be "stored" in them. Not all lysosomal diseases can be identified by this panel.
- Succinylacetone: Is a substance which accumulates in a disease called tyrosinemia. In this disease, a small protein fragment cannot be metabolized and toxic by-products form. Urine can be evaluated for succinylacetone, as can a blood spot sample.
- Urine Genetic Screen or Urine Organic Acids: May be ordered to screen for a number of metabolic diseases where an abnormal byproduct of the body's chemistry is excreted in the urine. Often, further testing is required to determine the significance of this result.
- Very Long Chain Fatty Acids (VLCFA): May be ordered if your child is suspected of having a peroxisomal defect. Peroxisomes are parts of cells that help digest fats and other substances. T
Tests for Viral Hepatitis
- Hepatitis A IgM (HA IgM): A hepatitis A IgM is positive when a patient has acute hepatitis A.
- Hepatitis B Surface Antigen (HBsAg): Hepatitis B surface antigen shows that the patient is infected with hepatitis B. It can be seen early in hepatitis B and persists in patients who are chronically infected.
- Hepatitis B Surface Antibody (HBsAb): Shows that a patient has gotten over hepatitis B infection or has been immunized.
- Hepatitis Be Antigen (HBeAg): Is present in a patient's bloodstream when their hepatitis B virus is growing actively. This is common in children with hepatitis B.
- Hepatitis Be Antibody (HBeAb): Shows that the patient has resolved rapid growth of the hepatitis B virus. Patients with this antibody can still be chronically infected.
- Hepatitis B DNA (HB DNA): Can show the presence or absence of the actual virus in the bloodstream. Quantitative
- Hepatitis B DNA: Shows the amount of hepatitis B virus in the bloodstream. There are a variety of techniques for measuring this virus, and the results of different tests are not always comparable.
- Hepatitis B Core IgG (HBc IgG): Is present, often for many years, in patients who have had hepatitis B in the past. It does not tell whether the patient is still infected.
- Hepatitis B core IgM, however, is positive with acute (recent) infection.
- Hepatitis C Antibody (HCAb): Is a screening test for hepatitis C. This can indicate infection with hepatitis C, although occasionally results are wrong (false positive).
- Hepatitis C RIBA: Looks for antibodies to specific hepatitis C proteins. The RIBA is more specific than the hepatitis C antibody.
- Hepatitis C PCR: This result can demonstrate the actual presence of the virus in the bloodstream.
- Quantitative Hepatitis C PCR: Can show the amount of virus in the bloodstream. This result can be expressed in International Units/ml or copies/ml. International units/ml multiplied by 2 is approximately equal to copies/ml.
- Hepatitis C Genotype: Can also be performed to determine which type of hepatitis C the patient has. Some types, such as type III, have a milder course than the most common type in the United States, which is type I-b.