title: Patients on subcutaneous allergen immunotherapy are at risk of intramuscular injections.
abstract: BACKGROUND
  Allergen-specific subcutaneous immunotherapy is an effective treatment for certain allergic disorders. Ideally, it should be administered into the subcutaneous space in the mid-posterolateral upper arm. Injections are commonly given using a standard allergy syringe with a needle length of 13 mm. Therefore, there is a risk of intramuscular administration if patients have a skin-to-muscle depth <13 mm, which may increase the risk of anaphylaxis. The objective of this study was to determine whether the needle length of a standard allergy syringe is appropriate for patients receiving subcutaneous immunotherapy.
  
  
  METHODS
  Ultrasounds of the left posterolateral arm were performed to measure skin-to-muscle depth in 200 adults receiving subcutaneous immunotherapy. The proportion of patients with a skin-to-muscle depth >13 mm vs. ≤13 mm was assessed and baseline characteristics of the two groups were compared. The proportion of patients with skin-to-muscle depths > 4 mm, 6 mm, 8 mm and 10 mm were also calculated. Multivariable logistic regression was performed to identify predictors of skin-to-muscle depth.
  
  
  RESULTS
  Of the 200 patients included in the study, 80% had a skin-to-muscle depth ≤13 mm; the majority (91%) had a skin-to-muscle depth >4 mm. Body mass index was found to be a significant predictor of skin-to-muscle-depth.
  
  
  CONCLUSIONS
  Most patients receiving subcutaneous immunotherapy have a skin-to-muscle depth less than the needle length of a standard allergy syringe (13 mm). These patients are at risk of receiving injections intramuscularly, which may increase the risk of anaphylaxis. Using a syringe with a needle length of 4 mm given at a 45° angle to the skin may decrease this risk.
authors.affiliation: Department of Anatomy and Cell Biology, McGill University, Montreal, QC, Canada.
authors.forename: Laura
authors.initials: L
authors.lastname: Kim
authors.affiliation: Michael D DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada ; Schulich School of Medicine & Dentistry, Western University, London, ON, Canada.
authors.forename: Immaculate
authors.initials: I
authors.lastname: Nevis
authors.affiliation: Department of Biology, University of Waterloo, Waterloo, ON, Canada.
authors.forename: Ryan
authors.initials: R
authors.lastname: Potts
authors.affiliation: Schulich School of Medicine & Dentistry, Western University, London, ON, Canada.
authors.forename: Clark
authors.initials: C
authors.lastname: Eeuwes
authors.affiliation: Schulich School of Medicine & Dentistry, Western University, London, ON, Canada.
authors.forename: Arunmozhi
authors.initials: A
authors.lastname: Dominic
authors.affiliation: Michael D DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada ; Schulich School of Medicine & Dentistry, Western University, London, ON, Canada.
authors.forename: Harold L
authors.initials: HL
authors.lastname: Kim
keywords: Allergen-specific immunotherapy; Allergy syringe; Injections; Needle length; Skin-to-muscle depth; Subcutaneous immunotherapy; Ultrasound