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Accuracy of clinical diagnosis in Down’s syndrome
  1. S Sivakumar,
  2. S Larkins
  1. Neonatal Unit and Regional Cytogenetic Laboratory, Birmingham Women’s Hospital, Edgbaston, Birmingham B15 2TG, UK;

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    Hindley and Medakkar1 showed that the clinical diagnosis of Down’s syndrome is inaccurate in one third of cases. We can imagine how stressful it will be for the parents if they have been told that their child may have Down’s syndrome and then subsequently karyotype proves to be normal. We conducted a retrospective study to estimate the accuracy of clinically suspicion in our region and in our hospital in particular.

    Using the regional cytogenetic laboratory database, all clinically suspected cases of Down’s syndrome born in the West Midland region during the period June 2000 to December 2002 were identified and karyotype results analysed. All babies identified from Birmingham Women’s Hospital were studied in detail by reviewing the case notes. Of 233 suspected cases from the whole West Midland region, 148 cases were positive by karyotype. Hence the accuracy of clinical suspicion was 64%. These figures were similar to results from Hindley and Medakkar,1 which showed this was 68% nationally and 64% in the Manchester region. However, from Birmingham Women’s Hospital, of 29 cases identified, 25 had a karyotype of trisomy 21 and so a higher accuracy rate of 86%.

    We cross checked the patient data from Birmingham Women’s Hospital with the rest of the region and found that there were no missed cases from our hospital. Based on the information given to parents before doing the karyotype, in 22 babies where parents were told the diagnosis of Down’s syndrome was felt to be certain, karyotype was positive in all 22. However, in seven cases where they were told a positive diagnosis was possible, four had a normal karyotype. All 25 cases that were confirmed positive were seen by a consultant before testing. In 23 of 25 babies, clinical suspicion occurred within the first 2 days of life; in two of the babies who were preterm, it took at least 3–4 weeks for clinical suspicion to develop. When we analysed the four negative cases, two were tested without being assessed by a consultant. One case was tested just based on profound hypotonia at 31 weeks but no other classical clinical features. In the final case, karyotyping was done to reassure the parents because there was repeated suspicion by two independent midwives and a registrar, but the consultant felt the baby was normal.

    Our data from Birmingham Women’s Hospital showed a favourable accuracy rate compared with the previous study.1 This can be explained by the fact that the tertiary hospital may have more experienced neonatalogists compared to the broad cohort of junior and senior paediatricians involved in other parts of the region. We believe that assessment by a senior paediatrician before testing may minimise the risk of negative results. There may be difficulty in diagnosing Down’s syndrome in preterm babies who may take some time to manifest classical features. We also agree with Hindley and Medakkar1 that some sort of scoring system like Fried’s index2 may also be useful in improving the accuracy of clinical diagnosis. However, a large prospective study is needed to evaluate those scoring systems.