PCR VS LATERAL FLOW IN BLOOD PARASITISM Sensitivity, subclinical infection, and the limits of diagnostics in real veterinary practice
Dr. Geoff Carullo, DVM, FPCCP, DPCVSCA
- Articles
- 4 min read
Blood parasitism remains one of the most common yet diagnostically challenging conditions in small animal practice, particularly in endemic regions.
Clinicians frequently encounter:
The increasing availability of PCR has led to the perception that it is the “gold standard.” However, this assumption must be interpreted in the context of parasite biology, host response, and real-world clinical limitations.
In practice, the most relevant pathogens include:
Each organism exhibits different:
These differences directly influence diagnostic outcomes.
A critical but often overlooked point:
– Most blood parasite lateral flow kits used in practice are antibody-based tests.
This is especially true for:
But not true for Dirofilaria immitis.
Meaning:
– A positive rapid test = evidence of exposure and immune response
– Not necessarily active infection
In contrast:
– PCR detects parasite DNA, representing organism presence at the time of sampling
Polymerase Chain Reaction (PCR)
Detects parasite nucleic acid (DNA) in blood.
Strengths:
Limitations:
Lateral Flow Assays (Rapid Test Kits)
Primarily detect:
Strengths:
Limitations:
Lateral Flow Positive, PCR Negative
Common in ehrlichiosis.
Possible explanations:
Lateral Flow Negative, PCR Positive
Seen in:
PCR detects infection before immune response is measurable.
In diseases such as Ehrlichia canis:
Acute phase → circulating organisms
Subclinical phase → reduced parasitemia
Chronic phase → localization in bone marrow and spleen
This reflects the concept of:
– pathogen sequestration
Diagnostic Implications
Thus:
– Negative PCR does not exclude infection
– Positive antibody test does not confirm active disease
Accurate diagnosis requires integration of:
1. Hematologic Findings
2. Clinical Context
3. Diagnostic Trends
4. Therapeutic Response
In selected cases, response to treatment supports presumptive diagnosis.
In many veterinary practices:
Under these conditions:
– Lateral flow assays serve as frontline screening tools
– Clinical judgment becomes central to decision-making
PCR is often described as “superior” due to its analytical sensitivity.
However:
– Sensitivity alone does not define clinical utility
Diagnostic accuracy depends on:
No single test provides complete certainty across all disease phases.
PCR and lateral flow assays are complementary tools.
PCR excels in detecting low-level and early infections
Lateral flow tests provide rapid, accessible clinical guidance
In subclinical and chronic infections, both have limitations.
Blood parasitism is not diagnosed by a single test.
– It is diagnosed through clinical reasoning supported by diagnostics
Not dictated by them.
Dr. Geoff Carullo is a Fellow and the current President of the Philippine College of Canine Practitioners.
Sharing this helps others understand what it really means to be a vet. If you found this valuable, like and follow for more insights.
