What is the reference range for anti–citrullinated protein antibody (ACPA)?

Updated: Jan 16, 2020
  • Author: Duane Kirksey, MD, MSc; Chief Editor: Eric B Staros, MD  more...
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Citrullination is a normal physiologic process that occurs in many dying cells. [1] Citrulline is a nonstandard amino acid that is produced by diminution of arginine residue present on certain human proteins by the peptidyl arginine-deiminase (PAD) enzyme. The PAD enzyme has several isoforms, of which PAD2 and PAD4 are expressed in inflammatory leukocytes. [2] The release of PAD from dying cells citrullinates extracellular proteins that contain arginine. Production of anti–citrullinated protein antibody (ACPA) depends on the genetic background of the patient.

  • < 20 EU/mL - Negative

  • 20-39 EU/mL - Weakly positive

  • 40-59 EU/mL - Moderately positive

  • >60 EU/mL - Strongly positive

  • Normal value - < 20 EU/mL

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