Page 755 - Veterinary Immunology, 10th Edition

Tests for Failure of Passive Transfer in Horses
VetBooks.ir Test Employed Relative Sensitivity (False Negatives) Relative Specificity (False Positives)

Glutaraldehyde coagulation 100
Latex agglutination 72 59
79
Membrane filter ELISA 90 79
Turbidimetric immunoassay 81 86
Infrared spectroscopy 93 97
From Crisman MV, Scarratt WK: Immunodeficiency disorders in horses, Vet Clin North Am
Equine Pract 24:299-310, 2008.

Single radial immunodiffusion is a more accurate method in that
it is both quantitative and specific for IgG. As described in Chapter

42, known standards are compared with the test serum by
measuring the diameter of precipitation produced in agar gel
containing an antiserum to equine IgG. A diagnosis of failure of
passive transfer is made in foals if IgG levels are less than 400
mg/dL and partial failure of passive transfer if IgG levels are

between 400 and 800 mg/dL. Unfortunately, radial
immunodiffusion is slow. It takes 18 to 24 hours to give a result and
is thus impractical when a rapid diagnosis is required.

A third method of measuring IgG levels is by use of a latex
agglutination test. The latex particles are coated with antiequine
IgG. In the presence of IgG, they agglutinate. This test can be
performed in about 10 minutes using either whole foal blood or
serum. It appears to be reliable and rapid but somewhat insensitive.

It is also possible to use a semiquantitative membrane-filter
enzyme-linked immunosorbent assay (ELISA) test to measure IgG
in a foal's serum. The color intensity of the reaction on the test filter

is compared with color calibration spots. A variant technique uses a
dipstick ELISA. Less satisfactory techniques include serum protein
electrophoresis and refractometry. (Refractometry is an acceptable,
rapid and convenient test of colostral IgG in calves but is less
reliable in foals, in which the wide range of values leads to

inaccuracy. It may severely underestimate serum IgG levels.) Point-
of-care portable analyzers also provide acceptable results in a
timely manner.

Management of Failure of Passive Transfer

In foals, an IgG concentration higher than 800 mg/dL is preferred,
but foals with immunoglobulin levels higher than 400 mg/dL will

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