title: Are medication restrictions before FOBT necessary?: practical advice based on a systematic review of the literature.
abstract: OBJECTIVE
  To determine whether medication interventions enhance the sensitivity and specificity of guaiac-based fecal occult blood testing (FOBT) when screening for colorectal cancer (CRC).
  
  
  METHODS
  We searched PubMed-MEDLINE, CINAHL, and the Cochrane databases using the MeSH headings occult blood, feces/analysis, and guaiac/analysis, linking them to variations of anticoagulants, heparin, warfarin, iron, aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), clopidogrel, cyclooxygenase-2 inhibitors, and ascorbic acid (vitamin C). Study selections were limited to English studies involving humans.
  
  
  METHODS
  All resulting titles and abstracts were reviewed for studies that included manipulation of medications associated with guaiac-based FOBT. If the study's relevance was unclear from the abstract, the full article was reviewed. The search resulted in 31 pertinent studies.
  
  
  RESULTS
  No studies addressed the effects of medication interventions on the sensitivity or specificity of FOBT screening. Randomized controlled trials, however, showed no increase in the rate of positive results among those taking NSAIDs. The literature is mixed regarding the effect of NSAIDs on the positive predictive value of a positive FOBT result, although no change in positive predictive value has been shown for warfarin. Iron will not affect FOBT results in vivo. Ascorbic acid might inhibit positive FOBT results both in vitro and in vivo, but it has not been studied in screening populations.
  
  
  CONCLUSIONS
  Studies evaluating the effects of medication intervention on FOBT screening for CRC are limited by their lower quality and because they do not address sensitivity and specificity. Available evidence, however, does not suggest a benefit from withholding NSAIDs, anticoagulant medications, or iron during the screening period. These recommendations should be abandoned in order to maximize adherence to screening. Positive FOBT results obtained among patients taking these medications deserve full evaluation for CRC. Until further studies clarify the effect of ascorbic acid on FOBT screening, withholding this medication before testing seems prudent.
authors.affiliation: Family Medical Centre, 500-400 Tache Ave, Winnipeg, MB R2H 3E1. gkonrad@sbgh.mb.ca
authors.forename: Gerald
authors.initials: G
authors.lastname: Konrad
authors.forename: Alan
authors.initials: A
authors.lastname: Katz
mesh_terms: D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage; D001205:Ascorbic Acid / Q000008:administration & dosage; D015179:Colorectal Neoplasms / Q000175:diagnosis*; D055088:Early Detection of Cancer / Q000379:methods*; D005189:False Positive Reactions; D006138:Guaiac; D006401:Hematologic Agents / Q000008:administration & dosage; D006801:Humans; D007202:Indicators and Reagents; D007501:Iron / Q000008:administration & dosage; D009780:Occult Blood; D004364:Pharmaceutical Preparations / Q000008:administration & dosage*; D011237:Predictive Value of Tests; D014131:Trace Elements / Q000008:administration & dosage; D014815:Vitamins / Q000008:administration & dosage; D028761:Withholding Treatment
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D006401:Hematologic Agents; D007202:Indicators and Reagents; D004364:Pharmaceutical Preparations; D014131:Trace Elements; D014815:Vitamins; D006138:Guaiac; D007501:Iron; D001205:Ascorbic Acid