Urinary analysis for Down's syndrome: is the measurement of urinary β-core the future of biochemical screening for Down's syndrome

Most Down's Screening protocols have concentrated on the analysis of oncofetal antigen levels present in serum. Urine has largely been ignored, but mass screening based on a urine text has several logistical advantages. We have examined the levels of urinary β-core as a marker of Down's syndrome. (β-core is a major immunoreactive degradation product of hCG and in particular its β-subunit). Elevated maternal serum hCG is the single most effective biochemical marker of Down's syndrome and levels are more than doubled. Measurement of elevated free β-subunit has been shown to be a superior discriminator than measurement of intact or total-hCG. This was shown by an increase in comparative serum levels from 2.04 to 2.41 multiples of the control population medium (MoM). The median MoM value of β-core for Down's cases in studies has varied between 4.38 and 6.28. The proportion of true Down's cases having a β-core value greater than the 95th centile of the controls varied from 61 to 93%. This is far superior to any single serum marker. If other complimentary urinary markers can be found urinary screening could replace serum screening not only because of the logistical advantages but increased sensitivity.