title: Interference of cerebrospinal fluid total protein measurement by povidone-iodine contamination.
abstract: BACKGROUND
  A falsely high cerebrospinal fluid (CSF) total protein (TP) result measured by pyrogallol red (PGR) method was suspected to be caused by preparation of the collection site with povidone-iodine (PVP-iodine) solution.
  
  
  METHODS
  CSF TP was evaluated for interference in samples with different final concentrations of PVP-iodine (up to 0.25% PVP and 0.025% iodine) or iodine alone (up to 0.025% iodine) using three methods: PGR, modified biuret and benzethonium chloride (BZTC). Interference exceeding ±20% of the baseline value is considered clinically significant according to the criterion defined by the College of American Pathologists.
  
  
  RESULTS
  There were positive interference with the PGR method and negative inference for the BZTC method in CSF samples spiked with PVP-iodine. The PVP-iodine (up to 0.25% PVP and 0.025% iodine) did not cause a clinically significant interference with the modified biuret method. PVP alone without iodine caused a positive interference with the PGR method but did not interfere with the modified biuret or the BZTC method. When the samples were spiked with iodine alone, none of the three methods was affected (change<20%) by iodine concentration up to 0.025%.
  
  
  CONCLUSIONS
  Contamination of CSF specimens with PVP-iodine can lead to interference with CSF TP measurements using PGR or BZTC methods.
authors.affiliation: Department of Laboratory Medicine, NIH Clinical Center, Building 10, Room 2C-249, Bethesda, MD 20892 USA.
authors.forename: Verena
authors.initials: V
authors.lastname: Gounden
authors.affiliation: Department of Laboratory Medicine, NIH Clinical Center, Building 10, Room 2C-249, Bethesda, MD 20892 USA.
authors.forename: David B
authors.initials: DB
authors.lastname: Sacks
authors.affiliation: Department of Laboratory Medicine, NIH Clinical Center, Building 10, Room 2C-249, Bethesda, MD 20892 USA. Electronic address: zhen.zhao@nih.gov.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhao
mesh_terms: D016477:Artifacts; D001558:Benzethonium; D002556:Cerebrospinal Fluid Proteins / Q000032:analysis*; D002624:Chemistry, Clinical / Q000379:methods*; D019963:Clinical Chemistry Tests / Q000379:methods; D006801:Humans; D011206:Povidone-Iodine; D011748:Pyrogallol / Q000031:analogs & derivatives; D013048:Specimen Handling / Q000379:methods*; D013053:Spectrophotometry / Q000379:methods
chemical_list: D002556:Cerebrospinal Fluid Proteins; D011748:Pyrogallol; D001558:Benzethonium; C058731:pyrogallol sulfonphthalein; D011206:Povidone-Iodine
keywords: Cerebrospinal fluid; Iodine; Povidone; Pre-analytical interference; Total protein