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Cholestasis can be excluded by normal levels of bile acids in plasma, the absence of lactate dehydrogenase, low levels of conjugated bilirubin, and ultrasound scan of the bile ducts. [citation needed] Vitamin B12 deficiency - elevated bilirubin levels (and MCV counts above 90–92) can be associated with a vitamin B12 deficiency. [citation needed]
Bilirubin (BR) (from the Latin for "red bile") is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates.This catabolism is a necessary process in the body's clearance of waste products that arise from the destruction of aged or abnormal red blood cells. [3]
In both settings of hemolysis mentioned above, only low levels of conjugated bilirubin may accumulate in the serum, with the amount falling within the normal limits of 4 percent of total bilirubin as conjugated bilirubin can be efficiently excreted in bile through being secreted across canalicular membrane. [25]
In biliary obstruction, below-normal amounts of conjugated bilirubin reach the intestine for conversion to urobilinogen. With limited urobilinogen available for reabsorption and excretion, the amount of urobilin found in the urine is low. High amounts of the soluble conjugated bilirubin enter the circulation where they are excreted via the kidneys.
In Dubin–Johnson syndrome, a mutation in multiple drug-resistance protein 2 (MRP2) causes a rise in conjugated bilirubin. [6] In acute appendicitis, total bilirubin can rise from 20.52 μmol/L to 143 μmol/L. In pregnant women, the total bilirubin level is low in all three trimesters. [6]
Jaundice, also known as icterus, is a yellowish or greenish pigmentation of the skin and sclera due to high bilirubin levels. [3] [6] Jaundice in adults is typically a sign indicating the presence of underlying diseases involving abnormal heme metabolism, liver dysfunction, or biliary-tract obstruction. [7]
In an Egyptian study, abnormally high levels of aflatoxin B1 and to a lesser extent aflatoxin B2 was found in liver tissue and blood of all neonates with biliary atresia. Aflatoxins may cause extensive damage to the hepatocytes leading to hepatitis and damage to bile ducts causing inflammation, adhesions and final obstruction of bile ducts. [17]
In the newborn liver, activity of glucuronyl transferase is only at 0.1-1% of adult levels, so conjugation of bilirubin is already reduced. Further inhibition of bilirubin conjugation leads to increased levels of bilirubin in the blood. [18] However, these results have not been supported by subsequent studies. [19]