Indirect (Unconjugated) Bilirubin — Serum
Unconjugated bilirubin reflects pre-hepatic bilirubin production. Pregnancy generally does not change normal ranges; elevations usually indicate hemolysis or impaired hepatic conjugation.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| mg/dL | 0.1 – 0.5 | 0.1 – 0.5 | 0.1 – 0.4 | 0.1 – 0.5 |
| µmol/L | 1.7 – 8.6 | 1.7 – 8.6 | 1.7 – 6.8 | 1.7 – 8.5 |
Pregnancy physiology
- Indirect bilirubin generally remains unchanged in pregnancy.
- Significant increases should prompt evaluation for hemolysis or hepatic dysfunction.
- Normal pregnancy does not cause indirect hyperbilirubinemia.
Causes of elevated indirect bilirubin
- Hemolysis (immune or non-immune)
- Gilbert syndrome (common)
- Crigler–Najjar syndrome (rare)
- Large hematoma resorption
- Ineffective erythropoiesis
- Medications impairing hepatic uptake
Evaluation should include CBC, LDH, haptoglobin, reticulocyte count, and smear.
Low indirect bilirubin
- Common and typically not clinically significant
- Normal in healthy pregnancy
- No evaluation needed unless other liver tests are abnormal
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31.
- Wallach J. Interpretation of Diagnostic Tests. 8th ed. LWW; 2007.
- Fischbach FT, Dunning MB. Manual of Laboratory and Diagnostic Tests. LWW; 2004.