Bilirubin:- Part 2 – Conjugated, Direct Bilirubin (Conjugated Hyperbilirubinemia)

Table of Contents
Conjugated, Direct Bilirubin
Sample
- This test is done in the serum of the patient.
- A random sample can be taken.
- This is ideal if the patient has nothing except water 4 to 8 hours before the sample.
- The sample is stable at 4 °C for 3 days.
- Protect the sample from the light because bilirubin is photo-oxidized (photosensitive).
Precautions for Conjugated, Direct Bilirubin
- Avoid hemolysis and lipemic serum, which will give a false result.
- Avoid drugs that will increase the total bilirubin level like:
- Anabolic steroids.
- Antibiotics.
- Antimalarial drugs.
- Chlorpropamide.
- Methotrexate.
- Antihypertensive drug-like methyldopa.
- Oral contraceptives.
- Antituberculous drugs like rifampin.
- Medications that will decrease the bilirubin level are:
- Penicillin.
- Caffein.
- Barbiturates.
- Exposure of the sample to sunlight or ultraviolet light may decrease the level.
Pathophysiology of Conjugated, Direct Bilirubin
- Bilirubin is yellow to the green pigment of bile derived from the porphyrin structure of hemoglobin.
- Excessive bilirubin within cells and the tissue causes jaundice (Icterus) or yellowness of the skin.
Mechanism of Hyperbilirubinemia:
- Destruction of the RBCs like hemolytic jaundice.
- Diseases affecting the metabolism and excretion of bilirubin in the liver.
- Obstruction like gall stones or pancreatic tumors and certain drugs like:
- Chlorpromazine and phenothiazine derivatives.
- Estrogen hormones.
- Halothane anesthetic drugs.
- Bilirubin estimation is one of the liver function tests.
- It is raised in the hepatic and post-hepatic types of jaundice.
- Clinically jaundice appears when the level of bilirubin is more than 2 mg/dl.
Direct (or conjugated) bilirubin:
- Direct bilirubin dissolves in water (water-soluble) and is synthesized in the liver from indirect bilirubin.
- The one-minute van den Berg reaction is called a direct reaction, and the bilirubin reaction is called direct bilirubin or conjugated bilirubin.
- While the bilirubin reacting in 30 minutes (with help of alcohol) is called indirect or unconjugated bilirubin.
Normal Values of Conjugated, Direct Bilirubin
- Total bilirubin = 0.3 to 1.0 mg/dL (5.1 to 17.0 mmol/L)
- Direct bilirubin = 0.1 to 0.3 mg/dL (1.0 to 5.1 mmol/L)
- Indirect bilirubin (total bilirubin minus direct bilirubin level) = 0.2–0.7 mg/dL
Another source Total bilirubin level
Age | Premature mg/dL | Full-term mg/dL | Adult mg/dL |
Cord blood | <2 | <2.0 | |
0 to 1 day | <8.0 | 1.4 to 8.7 | |
1 to 2 days | <12.0 | 3.4 to 11.5 | |
3 to 5 days | <16.0 | 1.5 to 12.0 | |
5 days to 60 years | 0.3 to 1.2 | ||
60 to 90 year | 0.2 to 1.1 | ||
>90 year | 0.2 to 0.9 |
Raised level of direct bilirubin is seen in:
- Gallstones.
- Gallbladder tumors.
- Inflammatory scarring or obstruction of extrahepatic ducts.
- Extensive liver metastasis.
- Dubin-Johnson syndrome.
- Rotor syndrome.
- Drugs may cause cholestasis.
Raised direct and indirect bilirubin is seen in:
- Hepatocellular disease.
- Hepatitis (viral disease).
- Cirrhosis.
- Dubon-Johnson syndrome.
The panic value that needs action are:
- Total bilirubin infants >15 mg/dL will require phototherapy.
- Total bilirubin in infants >20 mg/dL require blood transfusion.
- Untreated infants will get kernicterus which may lead to permanent brain damage.
Please see more details on bilirubin Total part 1.