Diagnostic Testing: Key Definitions and Guidelines for Use
Updated May 2026
Complete Blood Count
A complete blood count measures the number, size, and characteristics of red blood cells, white blood cells, and platelets to assess overall health.
- INFORMATION PROVIDED:
- Assessment of hematologic status compared to individual normal range.
- Hematologic changes are not necessarily specific to EEHV.
- WHEN TO USE IT:
- Weekly monitoring for at-risk calves.
- Daily monitoring of EEHV-HD cases to make informed treatment decisions.
Polymerase Chain Reaction (PCR)
Polymerase chain reaction is a molecular test that detects and amplifies viral DNA in a blood or trunk wash sample. Conventional PCR (cPCR) is qualitative, confirming the presence or absence of specific DNA in a sample. Quantitative PCR (qPCR) provides a precise measurement of viral load in a sample.
- INFORMATION PROVIDED (BLOOD):
- Presence of circulating virus (viremia) – Diagnostic for EEHV viremia
- Can occur due to a primary viremia or recrudescence
- WHEN TO USE IT (BLOOD):
- Screening at-risk calves.
- Diagnosis of EEHV active infection.
- Daily monitoring of EEHV-HD cases.
- INFORMATION PROVIDED (TRUNK WASH):
- Shedding of viral DNA in trunk secretions
- WHEN TO USE IT (TRUNK WASH):
- Routine herd screening.
- Determine potential for exposure of at-risk calves.
Serology
Serology is the detection of specific antibodies in the serum indicating prior exposure to that specific pathogen.
- INFORMATION PROVIDED:
- Successful transfer of maternal antibodies to a calf.
- Evidence of prior exposure/primary infection.
- WHEN TO USE IT:
- Routine monitoring of protective maternal antibody status in calves.
- Timing of vaccine administration.
- Determine risk level for EEHV-HD.
