What are the liver function test (LFT) abnormalities in patients with leptospirosis?

Liver Function Tests in Leptospirosis

In leptospirosis, liver function tests characteristically show a disproportionately elevated bilirubin (often markedly elevated) with only mild-to-moderate elevations in transaminases (AST/ALT), creating a distinctive cholestatic-hepatocellular mixed pattern. 1

Characteristic LFT Pattern

Bilirubin Elevation

• Bilirubin is typically high and often the most striking abnormality, frequently reaching levels consistent with clinical jaundice in severe cases (Weil's disease) 1
• The elevated bilirubin is disproportionate to the degree of transaminase elevation, which helps distinguish leptospirosis from other causes of acute hepatitis 1

Transaminase Elevations

• AST and ALT show only mild elevations despite significant clinical illness and jaundice 1
• This mild transaminase elevation contrasts sharply with the marked hyperbilirubinemia, creating a distinctive biochemical signature 1
• However, late in the disease course, progressive AST elevation (particularly when disproportionate to ALT) is an ominous prognostic sign 2

Alkaline Phosphatase

• Alkaline phosphatase is typically raised, contributing to the cholestatic component of the LFT pattern 1

Critical Prognostic Indicators

AST/ALT Ratio as a Mortality Predictor

• An AST/ALT ratio >3.0 predicts mortality in leptospirosis 2
• Patients who survived had mean AST/ALT ratios of 1.86 ± 0.64, while those who died had ratios of 5.65 ± 2.27 (p=0.006) 2
• All patients with ratios >3.0 died, while all patients with ratios <3.0 survived 2

Progressive AST Elevation

• Late exaggerated AST elevation without concomitant ALT rise indicates acute deterioration with impending death 2
• Serial monitoring of transaminases provides prognostic information beyond initial values 2

Other Laboratory Abnormalities

Renal Function

• Biochemical evidence of renal failure is common, as leptospirosis causes hepatorenal syndrome 1
• Urinalysis typically shows proteinuria and hematuria 1

Hematologic Findings

• Polymorphonuclear leukocytosis is common 1
• Thrombocytopenia occurs frequently 1
• Anemia may develop if significant hemorrhage has occurred 1
• Bleeding is due to capillary fragility, and coagulation tests are often normal despite hemorrhagic manifestations 1

Clinical Context and Timing

Disease Phases

• Leptospirosis follows a biphasic course: initial bacteremic phase (4-7 days) followed by an immune phase (1-3 days later) 1
• LFT abnormalities are most prominent during the immune phase when hepatorenal syndrome develops 1

Severity Spectrum

• In mild cases, LFT abnormalities may be minimal or absent 1
• In Weil's disease (severe leptospirosis), the combination of jaundice, renal failure, and hemorrhage with the characteristic LFT pattern is highly suggestive 1

Key Diagnostic Pitfalls

• Do not expect severe transaminase elevations (>10 times upper limit of normal) in leptospirosis—such elevations suggest alternative diagnoses like ischemic hepatitis, acute viral hepatitis, or drug-induced liver injury 3
• The mild transaminase elevation in leptospirosis contrasts with other causes of jaundice and can lead to diagnostic confusion if this pattern is not recognized 1
• Monitor AST/ALT ratio serially—a rising ratio >3.0 mandates intensive care and consideration of renal replacement therapy 2