Pennies are among the most common objects ingested, especially within the pediatric population.1,2 Conservative management of gastric coins has been the traditional approach. Two recent studies demonstrate that post-1982 pennies within the stomach may react differently than expected.3,4 Pennies produced before 1982 consist of 95% copper and 5% zinc; however, post-1982 pennies contain 97.6% zinc and 2.4% copper coating. We report the reaction of post-1982 pennies when placed in acid at gastric pH.
Three groups of Lincoln-head pennies were selected: 18 produced before 1982, 18 produced after 1982, and 18 post-1982 pennies damaged by rubbing the surface with emery cloth. Obviously damaged pennies were excluded. Each group of coins was immersed in hydrochloric acid (pH 1.9) to mimic stomach pH. Continuous gentle agitation of the acid baths was achieved with plastic 500 mL containers on a New Brunswick Scientific C1 shaker platform. Pennies were placed on their edges to maximize surface acid exposure. Because acid was neutralized within as few as 4 hours, acid solutions were replaced every 8 hours. The pennies were maintained at room temperature because heating the acid posed potential hazards.
The coins were inspected and weighed daily; photographs and roentgenograms were taken of the pennies at the start and end of the experiment. To determine if mass loss differed over time, a repeated measures analysis of variance was performed using baseline weight as a covariate.5
Chemical reactivity differed among the sets of pennies. Pre-1982 pennies had a rusted appearance and progressed to orange and red tints. The mass loss and gross changes of the pre-1982 pennies were consistent as a set (Table). The post-1982 (unscarred) pennies demonstrated the greatest variability of mass loss and appearance, and the majority darkened in color. Irregular corrosion and pitting became more prevalent with increased acid exposure. After 48 hours some pennies within this group demonstrated significant corrosion leading to sharp edges with flaking of strands of metal. Only some of these findings were detected with radiographs. The intentionally damaged pennies demonstrated consistent erosion and darkening primarily on the damaged side. The results of the repeated measure analysis of variance indicate a significant group-time interaction (P<.0001).
This study suggests that pennies produced after 1982 that become lodged in the stomach may fragment and develop sharp edges, and prolonged acid exposure may produce significant zinc absorption. Current recommendations of observation for spontaneous passage do not account for these possibilities.1 Increased monitoring of patients with pennies retained in the stomach >48 hours should be considered until further studies confirm whether observation alone provides adequate protection for all patients.
TABLE
Summary of penny weight
| Group | Initial weight* | Final weight* | 95% CI decrease in weight |
|---|---|---|---|
| Copper pennies (unscarred, 1960–1981) | 3.10 g (± 0.04) | 2.49 g (± 0.05) | (0.54–0.67) |
| Zinc pennies (unscarred, 1983–2000) | 2.50 g (± 0.02) | 2.15 g (± 0.26) | (0.28–0.42) |
| Zinc pennies (scarred, 1983–2000) | 2.50 g (± 0.02) | 2.12 g (± 0.05) | (0.32–0.46) |
| *Mean (± standard deviation). CI, confidence interval | |||
John M. Boltri, MD, Joshua E. Lane, MD,
Robert L. Vogel, PhD, and Dale E. Moore, PhD,
Department of Family Practice, Mercer University School of Medicine,
Macon, Ga. E-mail: boltri.john@mccg.org.