Bilirubin: Conjugated (Direct Bilirubin)
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Collection of sample
About 3 to 5 ml of blood is collected in a plain test tube, and blood is allowed to clot to get clear serum. In infants, the sample may be collected from the heel. The blood sample is centrifuged for 5 to 10 minutes and the serum is separated for the test.
The patient's serum is stable at 4° C for 3 days and protects it from the light.
Note: Bilirubin is photo-sensitive (photo-oxidized) so keep the sample in dark place otherwise false-negative results may obtain.
- Avoid sample from hemolysis
- Do not expose the sample to light. Exposure of sample to light may decrease the value.
- If there is a delay in performing the test then keep the sample in dark and refrigerate it.
- Avoid shaking of the test tube as it may lead to an inaccurate result.
- Serum bilirubin is a very useful test to evaluate liver functions. Raised level of bilirubin can be seen in the hepatic and post-hepatic type of jaundice.
- Clinically jaundice appears when the level of bilirubin is more than 2 mg/dl.
- Direct (or conjugated) bilirubin: It is water-soluble and dissolves in water and is synthesized in the liver form indirect bilirubin.
- Total bilirubin 0.3 to1.0 mg/dL or 5.1 to 17.0 mmol/L
- Direct bilirubin 0.1 to 0.3 mg/dL or 1.0 to 5.1 mmol/L
- Indirect bilirubin 0.2–0.7 mg/dL