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Editor,—Cole's proposed new chart1would indeed detect children with non-familial short stature. Whether it would detect “hidden” pathology is less certain—data from the Wessex Growth Study suggests not. Routine investigation of all children below Tanner's 3rd centile identified eight cases of silent pathology.2 Three of these, already on or above the current 0.4th centile, would clearly have lain above it on a conditional chart (figure 1), and might easily have been dismissed as normal. Parental heights may well inform the specialist, but their usefulness in a screening programme, without a full family history, is debatable.
Conditional standards demand that all heights are measured, not estimated, and should exclude those of abnormal stature.3Such conditions rarely hold. Few fathers, as we found, attend school medicals. In any case, by school entry, one in four Wessex children lived in single parent or reconstituted families.
Furthermore, almost half our short children, including those with pathology, had at least one parent below the 2nd centile. Short children, often assumed to be genetically short, may instead have inherited pathology. All very short children, regardless of familial height, deserve careful investigation.
Most children below the parent adjusted 0.4th centile would also fall below the unconditional 0.4th centile. As Cole admits, only when parental height is near or above average, are additional children likely to be referred. Our data show that children who are very short, even those with clear pathology, rarely have tall or even average parents. Indeed, mean parental height of all children with pathology was as low as those without (10th centile v7th centile).
In our study, some 10% of those short children with heights above the 0.4th centile had organic disease. As long as the fear of missed pathology remains, why not simply raise the screening threshold to a higher centile, perhaps the 2nd, and not complicate the process with a second chart?
Professor Cole comments:
Mulligan and Voss are concerned that the conditional chart does not identify hidden pathology, but they misunderstand the chart's purpose. It is designed for short children of tall families, not short children of short families—this group is already catered for with the unconditional chart. All the Wessex Growth Study cases of hidden pathology had shorter parents than average, so the conditional chart is not intended for them. Short children from tall families are relatively uncommon, so the cost of the extra screen is modest.
Despite what Mulligan and Voss say, familial heights do nothave to be measured—it is obviously desirable but not essential. Precision of measurement is much more important for the child than for the other family member(s), due to the shape of the critical region on the chart. And the father isnot essential for the assessment—the chart uses whatever family size information is available.
What Mulligan and Voss seem to be concerned about is the use of the 0.4th rather than the 2nd unconditional centile. It certainly increases the number of cases of pathology missed, but it also reduces the false positive rate by five sixths. Either way it has nothing whatever to do with familial height adjustment.