Liver function tests (LFTs or LFs), which include liver enzymes, are groups of clinical biochemistry laboratory blood assays designed to give information about the state of a patient's liver. Most liver diseases cause only mild symptoms initially, but it is vital that these diseases be detected early. Hepatic (liver) involvement in some diseases can be of crucial importance. This testing is performed by a medical technologist on a patient's serum or plasma sample obtained by phlebotomy. Some tests are associated with functionality (eg. albumin); some with cellular integrity (eg. transaminase) and some with conditions linked to the biliary tract (gamma-glutamyl transferase and alkaline phosphatase). Several biochemical tests are useful in the evaluation and management of patients with hepatic dysfunction. These tests can be used to (1) detect the presence of liver disease, (2) distinguish among different types of liver disorders, (3) gauge the extent of known liver damage, and (4) follow the response to treatment.
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Standard liver panel
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| Measurement | Significance | Reference range (Normal Values) |
| Alanine transaminase (ALT) | Alanine transaminase (ALT), also called Serum Glutamic Pyruvate Transaminase (SGPT) or Alanine aminotransferase (ALAT) is an enzyme present in hepatocytes (liver cells). When a cell is damaged, it leaks this enzyme into the blood, where it is measured. ALT rises dramatically in acute liver damage, such as viral hepatitis or paracetamol (acetaminophen) overdose. Elevations are often measured in multiples of the upper limit of normal (ULN). | 5 to 40 IU/L [1] |
| Aspartate transaminase (AST) | Aspartate transaminase (AST) also called Serum Glutamic Oxaloacetic Transaminase (SGOT) or aspartate aminotransferase (ASAT) is similar to ALT in that it is another enzyme associated with liver parenchymal cells. It is raised in acute liver damage, but is also present in red blood cells, and cardiac and skeletal muscle and is therefore not specific to the liver. The ratio of AST to ALT is sometimes useful in differentiating between causes of liver damage.[2][3] Elevated AST levels are not specific for liver damage, and AST has also been used as a cardiac marker. | 10 to 40 IU/L [1] |
| Alkaline phosphatase (ALP) | Alkaline phosphatase (ALP) is an enzyme in the cells lining the biliary ducts of the liver. ALP levels in plasma will rise with large bile duct obstruction, intrahepatic cholestasis or infiltrative diseases of the liver. ALP is also present in bone and placental tissue, so it is higher in growing children (as their bones are being remodelled) and elderly patients with Paget's disease. | 30 to 120 IU/L [1] |
| Total bilirubin (TBIL) | Bilirubin is a breakdown product of heme (a part of haemoglobin in red blood cells). The liver is responsible for clearing the blood of bilirubin. It does this by the following mechanism: bilirubin is taken up into hepatocytes, conjugated (modified to make it water-soluble), and secreted into the bile, which is excreted into the intestine.
Increased total bilirubin causes jaundice, and can signal a number of problems:
|
0.1 - 1.2 mg/dL |
| Direct bilirubin | The diagnosis is narrowed down further by looking at the levels of direct bilirubin.
|
0 - 0.3 mg/dL |
| Gamma glutamyl transpeptidase (GGT) | Although reasonably specific to the liver and a more sensitive marker for cholestatic damage than ALP, Gamma glutamyl transpeptidase (GGT) may be elevated with even minor, sub-clinical levels of liver dysfunction. It can also be helpful in identifying the cause of an isolated elevation in ALP. GGT is raised in alcohol toxicity (acute and chronic). | 0 to 51 IU/L [1] |
Other tests commonly requested alongside LFTs
| BMP/ELECTROLYTES: | |||
| Na+=140 | Cl-=100 | BUN=20 | / |
| Glu=150 | |||
| K+=4 | CO2=22 | PCr=1.0 | \ |
| ARTERIAL BLOOD GAS: | |||
| HCO3-=24 | paCO2=40 | paO2=95 | pH=7.40 |
| ALVEOLAR GAS: | |||
| pACO2=36 | pAO2=105 | A-a g=10 | |
| OTHER: | |||
| Ca=9.5 | PO4=1 | Mg2+=2.0 | |
| CK=55 | BE=-0.36 | AG=16 | |
| SERUM OSMOLARITY/RENAL: | |||
| PMO = 300 | PCO=295 | POG=5 | BUN:Cr=20 |
| URINALYSIS: | |||
| UNa+=80 | UCl-=100 | UAG=5 | FENa=0.95 |
| UK+=25 | USG=1.01 | UCr=60 | UO=800 |
| PROTEIN/GI/LIVER FUNCTION TESTS: | |||
| LDH=100 | TP=7.6 | AST=25 | TBIL=0.7 |
| ALP=71 | Alb=4.0 | ALT=40 | BC=0.5 |
| AST/ALT=0.6 | BU=0.2 | ||
| AF alb=3.0 | SAAG=1.0 | SOG=60 | |
| CSF: | |||
| CSF alb=30 | CSF glu=60 | CSF/S alb=7.5 | CSF/S glu=0.4 |
5' nucleotidase (5'NTD)
5' nucleotidase is another test specific for cholestasis or damage to the intra or extrahepatic biliary system, and in some laboratories, is used as a substitute for GGT for ascertaining whether an elevated ALP is of biliary or extra-biliary origin.
Coagulation test (e.g. INR)
The liver is responsible for the production of coagulation factors. The international normalized ratio (INR) measures the speed of a particular pathway of coagulation, comparing it to normal. If the INR is increased, it means it is taking longer than usual for blood to clot. The INR will only be increased if the liver is so damaged that synthesis of vitamin K-dependent coagulation factors has been impaired: it is not a sensitive measure of liver function.
It is very important to normalize the INR before operating on people with liver problems (usually by transfusion with blood plasma containing the deficient factors) as they could bleed excessively.
Serum glucose (BG, Glu)
The liver's ability to produce glucose (gluconeogenesis) is usually the last function to be lost in the setting of fulminant liver failure.
Lactate dehydrogenase (LDH)
Lactate dehydrogenase is an enzyme found in many body tissues, including the liver. Elevated levels of LDH may indicate liver damage.
See also
References
- ^ a b c d[broken citation]
- ^ Nyblom H, Berggren U, Balldin J, Olsson R (2004). "High AST/ALT ratio may indicate advanced alcoholic liver disease rather than heavy drinking". Alcohol Alcohol. 39 (4): 336–9. doi:. PMID 15208167. http://alcalc.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=15208167.
- ^ Nyblom H, Björnsson E, Simrén M, Aldenborg F, Almer S, Olsson R (September 2006). "The AST/ALT ratio as an indicator of cirrhosis in patients with PBC". Liver Int. 26 (7): 840–5. doi:. PMID 16911467. http://www3.interscience.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=1478-3223&date=2006&volume=26&issue=7&spage=840.
External links
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