, Volume 29, Issue 5, pp 622–628 | Cite as

An Investigation into the Stability and Sterility of Citric Acid Solutions Used for Cough Reflex Testing

  • James R. Falconer
  • Zimei Wu
  • Hugo Lau
  • Joanna Suen
  • Lucy Wang
  • Sarah Pottinger
  • Elaine Lee
  • Nawar Alazawi
  • Molly Kallesen
  • Derryn A. Gargiulo
  • Simon Swift
  • Darren SvirskisEmail author
Original Article


Citric acid is used in cough reflex testing in clinical and research settings to assess reflexive cough in patients at risk of swallowing disorders. To address a lack of knowledge in this area, this study investigated the stability and sterility of citric acid solutions. Triplicate solutions of citric acid (0.8 M) in isotonic saline were stored at 4 ± 2 °C for up to 28 days and analysed by high-performance liquid chromatography. Microbiological sterility of freshly prepared samples and bulk samples previously used for 2 weeks within the hospital was determined using a pour plate technique. Microbial survival in citric acid was determined by inoculating Staphylococcus aureus, Escherichia coli, or Candida albicans into citric acid solution and monitoring the number of colony-forming units/mL over 40 min. Citric acid solutions remained stable at 4 °C for 28 days (98.4 ± 1.8 % remained). The freshly prepared and clinical samples tested were sterile. However, viability studies revealed that citric acid solution allows for the survival of C. albicans but not for S. aureus or E. coli. The microbial survival study showed that citric acid kills S. aureus and E. coli but has no marked effect on C. albicans after 40 min. Citric acid samples at 0.8 M remained stable over the 4-week testing period, with viable microbial cells absent from samples tested. However, C. albicans has the ability to survive in citric acid solution if inadvertently introduced in practice. For this reason, in clinical and research practice it is suggested to use single-use aliquots prepared aseptically which can be stored for up to 28 days at 4 °C.


Citric acid Cough reflex testing Stability Sterility Tussigenic challenge Deglutition Deglutition disorders 


Conflict of interest

The authors have no conflicts of interest to declare.


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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  • James R. Falconer
    • 1
  • Zimei Wu
    • 1
  • Hugo Lau
    • 1
  • Joanna Suen
    • 1
  • Lucy Wang
    • 1
  • Sarah Pottinger
    • 1
  • Elaine Lee
    • 1
  • Nawar Alazawi
    • 1
  • Molly Kallesen
    • 2
  • Derryn A. Gargiulo
    • 1
  • Simon Swift
    • 3
  • Darren Svirskis
    • 1
    Email author
  1. 1.School of Pharmacy, Faculty of Medical and Health SciencesUniversity of AucklandAucklandNew Zealand
  2. 2.Capital & Coast DHBWellington HospitalWellingtonNew Zealand
  3. 3.Department of Molecular Medicine and PathologyUniversity of AucklandAucklandNew Zealand

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