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June 4, 1997

Determination of Deltoid Fat Pad ThicknessImplications for Needle Length in Adult Immunization

Author Affiliations

From the Mayo Vaccine Research Group, Clinical Pharmacology Unit (Drs Poland, Borrud, Jacobson, and McDermott), Section of Biostatistics, Health Sciences Evaluation (Dr Wollan), and Department of Diagnostic Radiology (Mr Brakke and Dr Charboneau), Mayo Clinic, Rochester, Minn. Dr McDermott is now with the Rice Clinic, St Paul, Minn.

JAMA. 1997;277(21):1709-1711. doi:10.1001/jama.1997.03540450065037

Objective.  —To measure deltoid fat pad thickness and determine the optimal needle length for deltoid intramuscular immunization in healthy adults.

Design, Setting, and Participants.  —Prospective study of 220 healthy health care workers (126 women, 94 men) at the Mayo Medical Center, Rochester, Minn.

Main Outcome Measures.  —Deltoid fat pad thickness determined by highresolution ultrasound scanning, weight, height, and mid-deltoid arm circumference.

Results.  —We found a highly significant difference between women and men in deltoid fat pad thickness, with women having a thicker deltoid fat pad (11.7 vs 8.3 mm; P<.001). Women had a greater deltoid skin-fold thickness than men (34.7 vs 17.2 mm, P<.001) and an equal body mass index. According to the ultrasound findings, a standard 16-mm (5/8-in) needle would not have reached 5 mm into muscle in 17% (16/94) of men and 48.4% (61/126) of women in this study.

Conclusions.  —Among healthy adults of the age range we studied, the following needle lengths appear to be appropriate for true deltoid intramuscular immunization: For men across the weight ranges we studied (59-118 kg), use of a 25-mm (1-in) needle would result in at least 5 mm of muscle penetration in all subjects. For women who weighed less than 60 kg, a 16-mm (5/8-in) needle would be sufficient to achieve muscle penetration of 5 mm. For women between 60 and 90 kg, a 25-mm (1-in) needle would be sufficient, and women greater than 90 kg would require a 38-mm (1.5-in) needle to ensure intramuscular administration.