Laboratory Work-Up for Leptospirosis in Children
For a child with suspected leptospirosis, obtain serology (IgM ELISA or microscopic agglutination test), PCR from blood or urine in the first week, and supportive laboratory tests including complete blood count, liver and renal function tests, creatine phosphokinase (CPK), and urinalysis.
Diagnostic Testing Algorithm
Phase-Based Approach
The laboratory work-up depends critically on timing of presentation:
First Week of Illness (Septicemic Phase):
- PCR testing from blood or urine is most useful during this early phase before antibodies develop 1
- Blood culture (though leptospires are slow-growing and may take months, limiting utility for acute diagnosis) 1
- Dark field microscopy is not recommended due to unreliability 1
After First Week (Immune Phase):
- Serology becomes the primary diagnostic method 1
- IgM ELISA or microscopic agglutination test (MAT) 2, 3
- Paired sera showing rising titers or single high titer confirms diagnosis 3
Essential Supportive Laboratory Tests
These help assess disease severity and organ involvement:
Hematology:
- Complete blood count (may show thrombocytopenia, leukocytosis)
Renal Function:
- Blood urea nitrogen and creatinine (renal failure occurs in severe cases) 3
- Urinalysis is particularly valuable and inexpensive - look for proteinuria, glucosuria, pyuria, hematuria, and granular casts indicating acute kidney injury 4
Hepatic Function:
- Liver enzymes and bilirubin (jaundice occurs in 18% of pediatric cases) 3
Muscle Involvement:
- Creatine phosphokinase (CPK) is a useful index of myositis, which is common in children with leptospirosis 3
Critical Clinical Context
High Index of Suspicion Required
Non-icteric leptospirosis in children presents with non-specific symptoms and is frequently missed 3. The most common presentations are:
Important Pitfalls
Overlapping infections complicate diagnosis - children may have concurrent Salmonella typhi, dengue hemorrhagic fever, or other tropical infections alongside leptospirosis 3. Consider leptospirosis testing in febrile children who test negative for malaria and other common tropical infections 4.
Delayed diagnosis increases mortality and morbidity 3, so maintain clinical suspicion in children with:
- Fever with myalgia
- Exposure to flood waters, rodents, or contaminated environments
- Meningitis or shock of unclear etiology (9% and 7% of cases respectively) 3
Limitations of Available Tests
The major limitation is that antibodies are lacking during the acute phase when treatment decisions must be made 1. This is why PCR testing early in illness is valuable when available, though molecular testing may not be accessible in resource-limited settings 1.