This sign has been estimated to have a sensitivity of 84% and specificity of 99% in diagnosing ectopic pregnancy. In the study estimating these values, the blob sign had a positive predictive value of 96% and a negative predictive value of 95%. The visualization of an empty extrauterine gestational sac is sometimes known as the "bagel sign", and is present in around 20% of cases. In another 20% of cases, there is visualization of a gestational sac containing a yolk sac or an embryo. Ectopic pregnancies where there is visualization of cardiac activity are sometimes termed "viable ectopic". The combination of a positive pregnancy test and the presence of what appears to be a normal intrauterine pregnancy does not exclude an ectopic pregnancy, since there may be either a heterotopic pregnancy or a "pseudosac", which is a collection of within the endometrial cavity that may be seen in up to 20% of women.A small amount of anechogenic-free fluid in the recto-uterine pouch is commonly found in both intrauterine and ectopic pregnancies. The presence of echogenic fluid is estimated at between 28 and 56% of women with an ectopic pregnancy, and strongly indicates the presence of hemoperitoneum. However, it does not necessarily result from tubal rupture but is commonly a result from leakage from the distal tubal opening. As a rule of thumb, the finding of free fluid is significant if it reaches the fundus or is present in the vesico-uterine pouch.
Most of it is oxidized into albendazole sulfoxide (also known as ricobendazole and albendazole oxide) in the liver by cytochrome P450 oxidases (CYPs) and a flavin-containing monooxygenase (FMO), which was discovered later. In humans, the cytochrome P450 oxidases are thought to include CYP3A4 and CYP1A1, while those in the rats are thought to be CYP2C6 and CYP2A1.Oxidation to albendazole sulfoxide by FMO produces R(+) enantiomers, while oxidation the cytochromes and by some enzymes in the gut epithelium produce S(-). Different species produce the R(+) and S(-) enantiomers in different quantities; humans, dogs, and most other species produce the R(+) enantiomer more (with the human AUC ratio being 80:20). Compared to the S(-) enantiomer, the R(+) has greater pharmacological activity, lasts longer in the bloodstream, is found in higher concentrations in the infected host tissues, and is found in higher concentrations within the parasites themselves. Some albendazole is also converted to hydroxyalbendazole, mainly by CYP2J2.For systemic parasites, albendazole acts as a prodrug, while albendazole sulfoxide reaches systemic circulation and acts as the real antihelminthic. Albendazole sulfoxide is able to cross the blood-brain barrier and enter the cerebrospinal fluid at 43% of plasma concentrations; its ability to enter the central nervous system allows it to treat neurocystocercosis.Albendazole sulfoxide is converted to the inactive albendazole sulfone by cytochrome P450 oxidases, thought to include CYP3A4 or CYP2C. Other inactive metabolites include: 2-aminosulfone, ω-hydroxysulfone, and β-hydroxysulfone.