Systematic Review and Meta-Analysis of Diagnostic Accuracy of Serum Refractometry and Brix Refractometry for the Diagnosis of Inadequate Transfer of Passive Immunity in Calves

S. Buczinski, E. Gicquel, G. Fecteau, Y. Takwoingi, M. Chigerwe, J. M. Vandeweerd

Research output: Contribution to journalReview articlepeer-review

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Abstract

BACKGROUND: Transfer of passive immunity in calves can be assessed by direct measurement of immunoglobulin G (IgG) by methods such as radial immunodiffusion (RID) or turbidimetric immunoassay (TIA). IgG can also be measured indirectly by methods such as serum refractometry (REF) or Brix refractometry (BRIX).

OBJECTIVES: To determine the accuracy of REF and BRIX for assessment of inadequate transfer of passive immunity (ITPI) in calves.

DESIGN: Systematic review and meta-analysis of diagnostic accuracy studies.

METHODS: Databases (PubMed and CAB Abstract, Searchable Proceedings of Animal Science) and Google Scholar were searched for relevant studies. Studies were eligible if the accuracy (sensitivity and specificity) of REF or BRIX was determined using direct measurement of IgG by RID or turbidimetry as the reference standard. The study population included calves <14 days old that were fed with natural colostrum (colostrum replacement products were excluded). Quality assessment was performed by the QUADAS-2 tool. Hierarchical models were used for meta-analysis.

RESULTS: From 1,291 references identified, 13 studies of 3,788 calves were included. Of these, 11 studies evaluated REF and 5 studies evaluated BRIX. The median (range) prevalence of ITPI (defined as calves with IgG <10 g/L by RID or TIA) was 21% (1.3-56%). Risk of bias and applicability concerns were generally low or unclear. For REF, summary estimates were obtained for 2 different cutoffs: 5.2 g/dL (6 studies) and 5.5 g/dL (5 studies). For the 5.2 g/dL cutoff, the summary sensitivity (95% CI) and specificity (95% CI) were 76.1% (63.8-85.2%) and 89.3% (82.3-93.7%), and 88.2% (80.2-93.3%) and 77.9% (74.5-81.0%) for the 5.5 g/dL cutoff. Due to the low number of studies using the same cutoffs, summary estimates could not be obtained for BRIX.

CONCLUSIONS AND CLINICAL IMPORTANCE: Despite their widespread use on dairy farms, evidence about the optimal strategy for using refractometry, including the optimal cutoff, are sparse (especially for BRIX). When using REF to rule out ITPI in herds, the 5.5 g/dL cutoff may be used whereas for ruling in ITPI, the 5.2 g/dL cutoff may be used.

Original languageEnglish
Pages (from-to)474-483
Number of pages10
JournalJournal of Veterinary Internal Medicine
Volume32
Issue number1
Early online date5 Dec 2017
DOIs
Publication statusPublished - 28 Jan 2018

Keywords

  • Journal Article
  • Review
  • accuracy
  • IgG
  • refrectometry
  • sensitivity
  • specificity

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