So you think you understand pregnancy tests?

Less than 40 years ago pregnancy was typically diagnosed by history and examination alone. While clinical skills always remain useful, there have been major advances in pregnancy testing that have been both clinically and medicolegally important. Like all diagnostic testing, pregnancy tests are not infallible, and it is very helpful for clinicians to understand their strengths and weaknesses.

Human chorionic gonadotropin (hCG) is redundantly called ‘human’ but appropriately named as the gonadotrophic hormone produced by the invading chorionic cells during implantation of the fertilised ovum. Like the pituitary gonadotropins, FSH and LH, hCG is made up of an identical alpha subunit but different beta subunits. Therefore old designation of ‘beta’ hCG, while just as redundant as ‘human’, is still commonly used, although in laboratory speak it could refer to the intact beta subunit rather than the beta subunit fragments that can appear after degradation, particularly in the urine.

Like most circulating proteins, hCG may have carbohydrate residues attached to it and hyperglycosylated hCG is a form of hCG commonly produced by gestational tumours (choriocarcinoma or hydatidiform mole), but is also produced in the very early stages of implantation. Not all laboratories run hCG assays that can detect the hyperglycosylated form of hCG and may poorly identify the presence ...

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