Conclusion on biochemicalassessment of liver function
Answers
Laboratory liver tests are broadly defined as tests useful in the evaluation and treatment of patients with hepatic dysfunction. The liver carries out metabolism of carbohydrate, protein and fats. Some of the enzymes and the end products of the metabolic pathway which are very sensitive for the abnormality occurred may be considered as biochemical marker of liver dysfunction. Some of the biochemical markers such as serum bilirubin, alanine amino transferase, aspartate amino transferase, ratio of aminotransferases, alkaline phosphatase, gamma glutamyl transferase, 5′ nucleotidase, ceruloplasmin, α-fetoprotein are considered in this article. An isolated or conjugated alteration of biochemical markers of liver damage in patients can challenge the clinicians during the diagnosis of disease related to liver directly or with some other organs. The term “liver chemistry tests” is a frequently used but poorly defined phrase that encompasses the numerous serum chemistries that can be assayed to assess hepatic function and/or injury.
Keywords: Laboratory liver test , bilirubin , alanine amino transferase , aspartate amino transferase , ratio of aminotransferases , alkaline phosphatase , gamma glutamyl transferase , 5′ nucleotidase , ceruloplasmin , α-fetoprotein
Laboratory Liver Tests
Serum Bilirubin
Bilirubin is the catabolic product of haemoglobin produced within the reticuloendothelial system, released in unconjugated form which enters into the liver, converted to conjugated forms bilirubin mono and diglucuronides by the enzyme UDP-glucuronyltransferase [1]. Normal serum total bilirubin varies from 2 to 21μmol/L. The indirect (unconjugated) bilirubin level is less than 12μmol/L and direct (conjugated) bilirubin less than 8μmol/L [2]. The serum bilirubin levels more than 17μmol/L suggest liver diseases and levels above 24μmol/L indicate abnormal laboratory liver tests [3, 4]. Jaundice occurs when bilirubin becomes visible within the sclera, skin, and mucous membranes at a blood concentration of around 40 μmol/L [5]. The occurrence of unconjugated hyperbilirubinemia due to over production of bilirubin, decreased hepatic uptake or conjugation or both. It is observed in genetic defect of UDP-glucuronyltransferase causing Gilbert\'s syndrome, Crigler-Najjar syndrome and reabsorption of large hematomas and ineffective erythropoiesis [6, 7]. In viral hepatitis, hepatocellular damage, toxic or ischemic liver injury higher levels of serum conjugated bilirubin is seen. Hyperbilirubinemia in acute viral hepatitis is directly proportional to the degree of histological injury of hepatocytes and the longer course of the disease [3]. It has been observed that the decrease of conjugated serum bilirubin is a bimodal fashion when the biliary obstruction is resolved [8]. Parenchymal liver diseases or incomplete extrahepatic obstruction due to biliary canaliculi give lower serum bilirubin value than those occur with malignant obstruction of common bile duct but the level remains normal in infiltrative diseases like tumours and granuloma [9]. Raised Serum bilirubin from 20.52 μmol/L to 143.64μmol/L in acute inflammation of appendix has been observed [10]. In normal asymptomatic pregnant women total and free bilirubin concentrations were significantly lower during all three trimesters and a decreased conjugated bilirubin was observed in the second and third trimesters . The recent study has shown that a high serum total bilirubin level may protect neurologic damage due to stroke .