Serum IgM concentrations in normal, fit horses and horses with lymphoma or other medical conditions.

The research study aims to establish the range of serum IgM and IgG concentrations in healthy adult horses and examine the accuracy of serum IgM levels as an indicator for diagnosing lymphoma in horses. The results indicate that while a high serum IgM concentration is unlikely to indicate lymphoma, a low level does not reliably confirm the presence of the disease, suggesting that this measure should not be used as a screening test for equine lymphoma.

Research Methodology and Participant Selection

• A total of 25 adult horses that were regularly exercised were involved in the study. They were assessed over a period of five months to establish the normal range for serum IgM and IgG concentrations.
• The concentration levels of IgM and IgG in the horses were measured at six-week intervals using a radial immunodiffusion assay, a method used to quantify specific proteins in a sample.
• The study also considered medical records of 103 adult horses admitted to the Cornell University Hospital for Animals. These horses were divided into two groups: those testing negative for lymphoma (34 horses) and those testing positive for lymphoma (18 horses).

Findings on IgM and IgG Concentrations

• In fit adult horses, the concentrations of serum IgM over five months varied between 50 to 242 mg/dL, with 20% of horses having IgM of 60 mg/dL or below. As a result, the study suggested the normal range for IgM to be 103 +/- 40 mg/dL and considered a concentration of 23 mg/dL or below as indicative of an IgM deficiency.
• On the other hand, serum IgG concentrations ranged from 1,372 to 3,032 mg/dL.

IgM Concentration’s Accuracy in Diagnosing Lymphoma

• Using the threshold of 60 mg/dL for serum IgM concentration, the sensitivity and specificity for detecting equine lymphoma was found to be 50% and 35%, respectively; this indicates a moderate ability for correctly diagnosing positive lymphoma cases and a low tendency for correctly identifying negative lymphoma cases.
• When the cut-off point was lowered to 23 mg/dL, the sensitivity dropped further to 28%, while the specificity improved to 88%. This implies a lower ability to correctly diagnose lymphoma cases, but a greater reliability in excluding non-lymphoma cases.
• Despite the improvement in specificity, the positive predictive value of 70% demonstrates an inadequate reliability in identifying horses with lymphoma when serum IgM is 23 mg/dL or below.

Conclusions

• Given the inconsistencies in correlation between serum IgM concentrations and lymphoma diagnosis, the researchers concluded that these measurements should not be used as a screening test for equine lymphoma.
• Instead, they suggest the normal range of 103 +/- 40 mg/dL as a reference for healthy horses’ serum IgM concentrations.