This well-conducted review investigated whether handheld metal detectors (HHMDs) can be used to reduce the number of X-rays needed in children thought to have swallowed coins. The authors' conclusion that the HHMD is an accurate and radiation-free alternative to X-rays is likely to be reliable.

To determine whether the use of a handheld metal detector (HHMD) can safely reduce the number of radiographs requested in cases of coin ingestion by children.

EMBASE (1980 to October 2004), MEDLINE (1966 to October 2004), OLDMEDLINE (1951 to 1965), MEDLINE In-Process and Other Non-Indexed Citations (October 2004), CINAHL (1982 to October 2004), AMED (1985 to September 2004), and EMB Reviews (October 2004) were searched; the search terms were reported. No language restrictions were applied. In addition, the reference lists of retrieved articles were examined, experts in the field were contacted, and six key journals were handsearched (1980 to September 2004).

Study designs of evaluations included in the review

All prospective studies of diagnostic performance were eligible for inclusion. Case reports, editorials and opinions were excluded.

Specific interventions included in the review

Studies of the ability of an HHMD to determine the presence or absence of ingested coins were eligible for inclusion. The manufacturers and models of HHMDs used in the included studies were reported.

Reference standard test against which the new test was compared

Eligible studies were required to use a minimum of a chest radiograph as the reference standard. The included studies used serial radiographs of the abdomen, chest and/or neck until the object was found, or repeat radiographs of the abdomen, chest and/or neck.

Participants included in the review

The studies were required to include children (age 17 years or younger) with suspected coin ingestion. The children in the included studies presented with suspected, witnessed or imaging technique proven, coin or metal foreign body indigestion.

Outcomes assessed in the review

The outcome measures had to include either the presence or absence of a coin on HHMD examination, or the accuracy of coin localisation. The review presented data on: correctly identified coins; missed coins; correctly localised to chest or abdomen coins; incorrectly localised to chest or abdomen coins; correctly excluded metal foreign bodies; false positives for ingested metal foreign bodies; the sensitivity for identifying ingested coins; the accuracy at localisation; and presumably the specificity of detecting and localising coins (overall specificity).

How were decisions on the relevance of primary studies made?

Two authors independently assessed abstracts retrieved from the searches for inclusion. Where the information in the abstract was considered insufficient for a decision, the full paper was obtained. Any disagreements were resolved by a third author.

The authors stated that the studies were scored for internal and external validity. Studies were excluded if the reference standard was not applied in all cases, or if the HHMD operator was not blinded to the results of the reference standard.

The authors did not explicitly state how the papers were assessed for validity, or how many reviewers performed the validity assessment. The authors of the primary studies were contacted when the methodology was inadequately reported.

The data were independently extracted by two reviewers and doubly entered into Meta-DiSc software. Where necessary, the reviewers dichotomised the location areas into abdominal (below the xiphisternum) or non-abdominal (xiphisternum or above).

How were the studies combined?

Pooled estimates of sensitivity and specificity, with 95% confidence intervals (CIs), were calculated using a Mantel-Haenszel fixed-effect model. Only data from doctor or radiographer operators, with prior instruction on how to use the HHMD, were used in the pooled analysis.

How were differences between studies investigated?

The chi-squared test was used to assess between-study heterogeneity.

Eleven diagnostic studies (n=739) were included in the review.

There was no evidence of statistically significant between-study heterogeneity, either for sensitivity (P=0.43) or specificity (P=1.0). The overall sensitivity of the HHMD for the detection of coins was 99.4% (95% CI: 98.0, 99.9; based on 9 studies), with a corresponding specificity of 100% (95% CI: 76.8, 100). The accuracy at localisation was 99.8% (95% CI: 98.5, 100; based on 11 studies).

The authors estimated that, based on PACS (Picture Archiving and Communications System) costs of neck, chest and abdominal radiographs, the cost of purchasing an HHMD would be recovered after four cases.

HHMD is an accurate, radiation free and cost-effective method of identifying and localising coins ingested by children.

This was a well conducted and reported review, which addressed a clearly stated research question that was defined by relevant inclusion criteria. A thorough search strategy was reported and no language restrictions were applied. The review methodology was clearly reported and measures were taken to minimise the introduction of error and bias during the study selection and data extraction processes. A limited assessment of the methodological quality of the studies was reported, and this was used to provide additional inclusion criteria (studies that did not meet the three quality criteria were excluded). Details of studies, including their results, were clearly and fully reported. The methods used to generate pooled estimates of test performance were clear and appropriately applied. The authors' conclusions follow from the data presented. However, cost-effectiveness and safety assessments were not part of the systematic review.

Practice: The authors stated that HHMDs should be used by all UK emergency departments, and they presented an algorithm for the investigation of children with suspected coin ingestion. They further stated that personnel operating HHMDs should have a demonstration and practise sessions before use, in which the possible causes of false-positive and false-negative results are highlighted. The authors suggested that parents of children with ingested coins should be advised only to return if the child becomes symptomatic after coin ingestion.

Research: The authors made no specific recommendations for future research.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.