Does leptospirosis cause transaminitis or isolated hyperbilirubinemia?

Leptospirosis Causes Hyperbilirubinemia with Mild Transaminitis, Not Isolated Hyperbilirubinemia

Leptospirosis characteristically presents with high bilirubin accompanied by mild elevation of transaminases—not isolated hyperbilirubinemia. This distinctive pattern is a key diagnostic feature that differentiates leptospirosis from other causes of jaundice 1.

The Characteristic Hepatic Pattern

The liver involvement in leptospirosis follows a specific biochemical signature:

• High bilirubin (often markedly elevated, particularly in severe Weil's disease)
• Mild transaminase elevation (ALT/AST typically only mildly elevated, not proportionate to the degree of jaundice)
• This creates a disproportionate pattern: severe hyperbilirubinemia with relatively modest transaminase elevation 1

Multiple recent case reports from 2026 confirm this pattern consistently. One case described "isolated, mildly elevated bilirubin and transaminases" 2, another reported "marked hyperbilirubinemia with transaminitis" 3, and a third noted "transaminitis with direct hyperbilirubinemia" 4, 5, 6.

Why This Pattern Matters Clinically

This biochemical signature reflects the underlying pathophysiology:

• The hyperbilirubinemia is predominantly conjugated (direct) bilirubin 1
• The liver injury is primarily cholestatic rather than hepatocellular
• The mechanism involves capillary damage and immune-mediated injury, not massive hepatocyte necrosis
• This explains why bilirubin rises dramatically while transaminases remain only mildly elevated

Diagnostic Algorithm for Hepatic Abnormalities in Suspected Leptospirosis

When evaluating a febrile patient with potential leptospirosis exposure:

1. Check both bilirubin AND transaminases together—never interpret bilirubin in isolation
2. Look for the characteristic pattern: High bilirubin (often >5-10 mg/dL in severe cases) with ALT/AST only 2-5 times upper limit of normal
3. Confirm direct (conjugated) hyperbilirubinemia—this should be >35% of total bilirubin in leptospirosis-related liver injury
4. Assess for other supportive features: thrombocytopenia, renal dysfunction, and myalgia (especially calf pain) 1

Common Pitfall to Avoid

Do not dismiss leptospirosis because transaminases are only mildly elevated. Clinicians accustomed to viral hepatitis (where transaminases are markedly elevated) may incorrectly assume that mild transaminase elevation rules out significant liver involvement. In leptospirosis, the opposite is true—the combination of high bilirubin with disproportionately mild transaminitis is actually characteristic of the disease 1.

A meta-analysis of febrile returning travelers demonstrated that hyperbilirubinemia was 5-7 times more likely in malaria than non-malaria patients 7, highlighting that this pattern of disproportionate hyperbilirubinemia is seen in other tropical infections as well, making the full clinical context essential.

Additional Laboratory Context

The hepatic abnormalities in leptospirosis typically occur alongside:

• Thrombocytopenia (very common)
• Elevated creatinine (renal involvement is frequent)
• Polymorphonuclear leukocytosis (may be present)
• Proteinuria and hematuria on urinalysis 1

Recent case series confirm multi-organ involvement is the rule rather than exception, with one 2026 study reporting 15.1% of leptospirosis cases had coinfections that further complicated the clinical picture 8.