What is the likely diagnosis for a patient with mildly elevated total bilirubin (hyperbilirubinemia) and indirect bilirubin, normal liver function tests (LFTs), and a normal complete blood count (CBC) aside from an elevated red cell distribution width (RDW), but no anemia?

Gilbert Syndrome: Most Likely Diagnosis

Your laboratory findings are most consistent with Gilbert syndrome, a benign hereditary condition requiring no treatment and warranting complete reassurance. 1, 2

Diagnostic Interpretation

Your bilirubin pattern strongly supports Gilbert syndrome:

• Indirect (unconjugated) bilirubin comprises 84% of total bilirubin (1.6 mg/dL out of 1.9 mg/dL), which exceeds the diagnostic threshold 1, 2
• Gilbert syndrome is diagnosed when conjugated bilirubin represents less than 20-30% of total bilirubin in the absence of hemolysis 1, 2
• Your direct bilirubin is only 16% of total (0.3/1.9), clearly meeting this criterion 2

Why This Pattern Matters

Gilbert syndrome results from reduced activity of the enzyme uridine 5'-diphospho-glucuronosyltransferase (UGT1A1), causing impaired bilirubin conjugation. 1, 2 This affects approximately 5-10% of the population and is completely benign 1, 2.

The key distinguishing features in your case:

• Normal liver function tests (ALT, AST, ALP) exclude hepatocellular injury or cholestatic disease 1, 2
• No anemia on CBC rules out hemolytic causes of unconjugated hyperbilirubinemia 1, 2
• Mildly elevated total bilirubin (1.9 mg/dL) is typical, as Gilbert syndrome rarely exceeds 4-5 mg/dL 2

The Elevated RDW Finding

The elevated red cell distribution width (RDW) without anemia is an interesting finding that may actually support the diagnosis:

• Persons with Gilbert syndrome have been shown to have relatively increased red blood cell mass compared to controls 3
• This increased red cell turnover, even without frank anemia, contributes additional bilirubin load that the impaired conjugation system cannot fully process 3
• The elevated RDW may reflect subtle variations in red cell populations related to this increased turnover 3

Clinical Significance and Management

Gilbert syndrome is entirely benign and requires no treatment. 1, 2 Important points:

• Bilirubin levels fluctuate with fasting, illness, stress, and exertion—this is expected and harmless 2
• No risk of liver disease progression exists with this condition 1, 2
• Avoid unnecessary diagnostic testing once the diagnosis is established 2

When to Consider Alternative Diagnoses

You should reconsider if any of these features develop:

• Conjugated bilirubin >30% of total would suggest hepatobiliary disease rather than Gilbert syndrome 1, 2
• Elevated liver enzymes (ALT, AST) would indicate hepatocellular injury requiring further evaluation 1, 2
• Development of anemia would necessitate hemolysis workup 1, 2
• Total bilirubin >5 mg/dL is unusual for Gilbert syndrome and warrants additional investigation 2

Confirmatory Testing (If Needed)

Genetic testing for UGT1A1 mutations can provide definitive confirmation, especially if diagnostic uncertainty exists or if bilirubin elevations occur with other liver test abnormalities 1, 2. However, this is typically unnecessary when the clinical picture is clear.

Common Pitfall to Avoid

Do not misattribute this benign finding to drug toxicity or other liver pathology. 2 Accurately identifying Gilbert syndrome prevents unnecessary diagnostic procedures, inappropriate treatment discontinuations, and patient anxiety about non-existent liver disease 2.