CT Abdo/Pelvis & Pregnancy Testing

Radiology are now requesting blood pregnancy testing reproductive females from 10-35days from last period. But what is wrong with urine pregnancy testing?

National Guidance

In the IR (ME)R and HPA (health protection agency), guidance have both questioned the reliability of Urine Pregnancy testing in the early stages of pregnancy i.e. prior to missing your first period.

Urine Pregnancy Testing

The evidence for this seems to revolve around the following study: Natural limits of pregnancy testing in relation to the expected menstrual period. this showed that Urine Pregnancy test only reached peak sensitivity (97%) at 1 week after the first missed period (i.e. 35 days).

If Urine Pregnancy Testing is used prior to the 1st day of the first missed period the sensitivity is 90% i.e. potentially misses 1:10 pregnancies

Why is it Important?

HPA guidance presents evidence in their guidance that in the early weeks of pregnancy. Foetuses exposed to high doses of radiation >10mGy (i.e. CT Abdo/Pelvis) confers a 1:200 – 1:1000 chance of developing childhood cancer (background rate <1:1’000’000). This is based on evidence from the 1980’s

What if it’s Life-Threatening?

If delaying the scan to wait for a Blood Pregnancy Test may compromise the patients health. This needs to be communicated to the agreeing radiologist, and the decision making entered in the patients notes.

Consent must be documented, whether this be active consent or best interest. However, the patient should understand that although there is a theoretical increased risk of childhood cancer, compromising the patients health will likely have much more immediate and untreatable effects on the foetus.

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