Measurement of Serum IgG in Foals by Radial Immunodiffusion and Automated Turbidimetric Immunoassay

Abstract

Hypogammaglobulinemia as a result of failure of transfer of passive immunity (FTPI) is an important risk factor for infectious disease in neonatal foals. The current gold standard for determining serum immunoglobulin concentrations is radial immunodiffusion (RID). The purpose of this study was to compare immunoglobulin concentrations measured by RID with those determined by an automated turbidimetric immunoassay (TIA), which has a much shorter turnaround time. Immunoglobulin concentrations were measured by both RID and TIA in serum collected from 84 neonatal foals. Sixty-seven foals had results within the linear range for both assays. Sensitivity and specificity of TIA for diagnosis of FTPI with IgG Յ 800 mg/dL were 0.81 (95% CI 0.70-0.88) and 0.86 (95% CI 0.76-0.93) and with IgG Յ 400 mg/dL were 0.63 (95% CI 0.35-0.86) and 0.92 (95% CI 0.87-0.95), respectively. A significant linear relationship was found between IgG concentrations determined by TIA and RID (TIA ϭ 0.9511RID ϩ 8.4354; R 2 ϭ .59, P Ͻ .0001). The coefficients of variation for between-run and within-run precision for the TIA were 2.5 and 3%, respectively. Storage of samples from 10 foals at Ϫ20ЊC for 10-12 months resulted in a reduction in TIAmeasured serum IgG concentration of Ϫ17.6% (SD ϭ 3.7%), indicating that long-term storage of samples at Ϫ20ЊC should be avoided. The results of this study indicate that measurement of serum IgG by TIA can be used to evaluate foals for FTPI.Key words: Horse; IgG measurement; Immunoglobulin; Transfer of immunity.T ransfer of passive immunity is crucial to the health of a neonatal foal. In contrast to cats and dogs, no immunoglobulin transfer occurs across the equine placenta, and foals are born hypogammaglobulinemic. Therefore, immunoglobulin transfer in the initial postnatal period by ingestion of good-quality colostrum is critical for the establishment of passive immunity in the foal. The rate of uptake of colostral immunoglobulins by the foal's small intestinal epithelial cells is highest in the 1st 6-8 hours after birth and then begins to decline. Immunoglobulin is not absorbed after 24-36 hours of age. If a foal fails to suckle in the immediate postpartum period, there is a low to absent concentration of immunoglobulin, resulting in a high incidence of neonatal infectious disease. [1][2][3][4] Failure of transfer of passive immunity (FTPI) can result from injury or illness in the neonate, inadequate immunoglobulin production by the dam, or failure of the neonate to absorb the ingested colostrum. 4,5 The incidence of FTPI in foals is estimated to be between 2.9 and 25%. 6 Foals that are immunodeficient because of FTPI are susceptible to many infections, especially septicemia, omphalophlebitis, septic arthritis, and respiratory infections. 1-4 Thus, a sensitive and specific diagnostic test to identify FTPI is valuable in the management of neonatal foals.The current gold standard for determination of serum immunoglobulin concentration is the serial radial immunodiffusion (RID) assay. 7,8 In this test, serum is ...

Correlation of Serum IgG Concentration in Foals and Refractometry Index of the Dam’s Pre- and Post-Parturient Colostrums: An Assessment for Failure of Passive Transfer in Foals

“…The latter test is effective in assessing a foal with IgG concentrations<400 mg/dl and<800 mg/dl when the cutoff value is set to 6% and 10%, respectively. Both tests are as accurate as other commercially available test kits reported by a previous study [12]. The results particularly suggest that the measurement of DVRI is quite useful in assessing FPT in foals as an initial screening test "stall-side" because it has a relatively high NPV, and of more importance, it is procedurally easier to perform, allows for rapid interpretation and is more cost-effective than any other commercially available test kit.…”

“…Measuring STP is an indirect way to estimate the IgG concentration and is based on the assumption that low STP after nursing colostrum reflects a failure in transfer of maternal antibodies [18]. On the other hand, several studies have suggested that STP concentrations using a cutoff value of<4.6 or 4.7 g/dl are likely to indicate FPT and that measurement of the STP concentration might be used as a guide to assess the IgG concentration if no other test is available or as an adjunctive test [12,46]. In this study, the STP concentration was significantly correlated with the serum IgG concentration (r=0.86), which confirms the results obtained in a previous study (r=0.85) [41].…”

“…Refractometry was chosen as an early screening test for measuring STP concentration in this study, because it can be rapid, inexpensive and convenient and does not require sending of samples to a specialized laboratory. However, the results of several reports have indicated that this test is an unreliable indicator of FPT in foals [12,34,41]. It is considered that the cause of these results is the wide range of STP concentrations in newborn foals before nursing colostrum [41], unlike in calves [45].…”

“…However, results of SRID test are generally not available for 24 hr. The 24-hr delay in obtaining test results decreases the usefulness of this test for routine use on a breeding farm, in a field situation or at a veterinary clinic because rapid results are required for therapeutic intervention in FPT cases in foals [1].Several rapid tests for practical use have been used to estimate IgG concentrations in foals, including the glutaraldehyde coagulation test [5,9], zinc sulfate turbidity test [4,41], latex agglutination test [22,47], enzyme immunoassay [6,38], turbidimetric immunoassay [4,11] and measurement of serum total protein (STP) concentration [12,41]. Many of these tests are now commercially available as kits for use on a breeding farm or at a veterinary clinic.…”

“…This means this test may be routinely used on a breeding farm or in a field situation, because rapid results are required for determin-ing the necessity of therapeutic intervention in FPT cases in foals. However, several reports have indicated that this test is an unreliable indicator of FPT in foals [12,34,41] because unlike in calves, there is a wide range of STP concentrations in newborn foals [41,45].…”