New alert over home pregnancy tests

Women who use home pregnancy tests were today warned the kits may give inaccurate results and most are not as reliable as manufacturers claim.

A study of leading brands suggests many that purport to work from the first day of a missed period do not pick up pregnancies until much later. Others have technical flaws resulting in positive readings when the woman is not pregnant. Scientists have called on manufacturers to review their claims, warning false results could have devastating consequences.

The study comes a day after regulators said they had found a fault with a testing kit used by GPs and hospitals.

The Medicines and Healthcare Products Regulatory Agency said women given a negative result by the SAS 1 Step system will be tested again.

Almost all brands claim to be at least 99 per cent accurate from the first day of the missed period, with some purporting to work three days before the period is due. Millions of women use the kits, which work by picking up traces of the hormone human chorionic gonadotropin (hCG) in urine.

But a study in the American Journal of Obstetrics and Gynaecology found less than half produced clearly positive results even when dipped into urine containing high levels of the hormone.

Results were even worse when the kits - available both here and in the United States - were tested on urine with the lowest possible level of hCG on the first day of a missed period.

Professor Laurence Cole, who led the study, said: "Overall, the brands were unreliable in providing a clearly positive result at the suggested reading time."

The amount of hCG in urine varies widely among pregnant women on the first day of the missed period, ranging from 12.4 milli-international units (mIU) per millilitre, to more than 100 mIU.

Many tests claim to be able to detect pregnancies from samples with a minimum of 12.5 mIU, and say the results can be read in minutes. But the study reveals that most kits give false negative results when tested at that level.

Only two kits - Clear Blue Easy, One Minute; and Answer - gave clear and accurate results in the stated time frame. Clear positive results appeared on a handful of other tests if the display panel was examined after a longer reading time of 10 minutes.

Even when tested on far higher hCG levels, many tests gave only faintly discernible positive results.

The worst performing kits were Confirm, Eckerd One-Step and Equate - all of which failed to produce clear positive results at the highest hormone concentration.

Three out of six Clear Choice kits gave positive results when dipped in urine containing no hCG. Nobody at maker Phamatech was available to comment.