Block B - testing for pregnancy

Question 1

1350 BCE egyptian papyrus ?

Answer 1

Urine-based pregnancy in an ancient Egyptian papyrus. Woman urinated on wheat and barley seeds : “If the barley grows, it means a male child. If the wheat grows, it means a female child. If both do not grow, she will not bear at all.” Testing in 1963 found that 70 percent of the time, the urine of pregnant women did promote growth, while the urine of non-pregnant women and men did not.

Question 2

17th centrury piss prophet ?

Answer 2

piss prophets” In a 1552 text, pregnancy urine was described as: “clear pale lemon color leaning toward off-white, having a cloud on its surface.” Other tests included mixing wine with urine and observing the results. Alcohol reacts with certain proteins in urine, so this may have had a moderate success rate

Question 3

1890’s breakthrough ?

Answer 3

Many physicians began to describe the workings of chemicals in the body, suggesting that “internal secretions” by certain organs were crucial to an understanding of human biology. Ernest Starling named these chemical messengers “hormones.”

Question 4

A-Z test 1927 ?

Answer 4

Aschheim and Zondek described a test (known as the A-Z test) which identified the presence of hCG in urine. Urine was injected into an immature rat or mouse. If not pregnant, there would be no reaction. If pregnant, the rat would show an estrous reaction (be in heat). This was also done in rabbits where ovulation was used as a positive indicator.

Question 5

1948 frog test ?

Answer 5

Frog test. Urine injected into male frogs and if they expelled sperm cells in their urine the urine was from a pregnant woman (Miller and Wiltberger).

Question 6

1960 hemagglutination inhibition test ?

Answer 6

A “hemagglutination inhibition test” first immunoassay for pregnancy was developed by Wide and Gemzell.

Question 7

1966 Midgley first radioimmunoassay for HcG ?

Answer 7

Midgley described the first radioimmunoassay for hCG, but the test still could not differentiate between hCG and luteinizing hormone. Several other laboratories reported improvements on this test but did not solve this basic problem.

Question 8

what hormone is raised earliest in pregnancy and what is associated with pregnancy?

Answer 8

HcG

Pregnancy is associated with an increase in blood and urine levels of:HCG (Human Chorionic Gonadotropin), Oestrogen/Estrogen and Progesterone.

Question 9

before modern tests animals were used , how was this not the best ?

Answer 9

Historically serum or urine would be tested in biological assays using animals (as previously mentioned). This is not an ideal situation as animals are expensive to keep , these tests are not very reliable as well as ethical considerations. Furthermore , the time taken to give answer is long.

Question 10

what allows immunoassays to occur ?

Answer 10

HCG was cloned and antibodies raised to it allowing development of immunoassays.

Question 11

3 types of immunoassays ?

Answer 11

There are 3 main types used: Inhibition of latex agglutination used in a clinical setting , radioimmunoassay which is also clinical. A Dipstick can be used at home as well as a clinical setting.

Question 12

inhibition of latex agglutination ?

Answer 12

Rabbit anti-HCG is mixed with urine or serum sample, If HCG is present it will be bound thus removing anti-HCG from further reactions. If HCG is not present, the mixture will contain free anti-HCG. The latex beads coated with HCG are added to sample, Agglutination is a Negative result (NOT PREGNANT). If there is No Agglutination then the person is positive (PREGNANT).

Question 13

why does no agglutination happen if pregnant ?

Answer 13

No agglutination as the binding sites on antibodies have been previously filed with HCG from the sample, this is a positive result. `

Question 14

why does agglutination happen if not pregnant ?

Answer 14

This is a negative result, as the antibodies bind to the HCG beads as no HCG is in the sample so agglutination occurs with the latex beads.

Question 15

radioimmunoassay (RIA)

Answer 15

Rabbit anti-HCG is mixed with urine or serum sample. If HCG is present it will be bound thus removing anti-HCG from further reactions. If HCG is not present, the mixture will contain free anti-HCG. Radio-labelled HCG is added to sample , Highly Radioactive Negative after washing then (NOT PREGNANT). If the sample is not Radioactive then Positive (PREGNANT).

Question 16

how come pregnant then no radioactivity ?

Answer 16

The radiolabelled Hcg cannot be bound by the antibody as the binding sites are bound to HCG present in the sample, no radioactivity of and person is pregnant.

Question 17

how come not pregnant if radioactivity ?

Answer 17

The radiolabelled HcG is bound by the antibody as there is no HcG in the sample so that there is high radioactivity and person is not pregnant

Question 18

dipstick lateral flow assay ?

Answer 18

Rabbit anti-HCG is bound to colored latex beads and dried onto filter paper. When mixed with urine. If HCG is present it will be bound by Ab , If HCG is not present -it is not bound!

The Latex beads travel up the filter paper where they pass a line of immobilized anti-HCG

If HCG is present on the latex beads, they will be bound by Ab and the beads stopped AND FORM A LINE. If HCG is not present on the beads, they continue to move up the filter.

Some Latex beads travel further up the filter paper where they pass a line of immobilized anti-rabbit IgG. They are bound by Ab and the beads stopped AND FORM A LINE as a positive control.

Question 19

how many lines for pregnancy ?

Answer 19

2

Question 20

how many lines for no pregnancy ?

Answer 20

There is only one line , no second line as there is no HcG present. The single shows the control and the test has worked as the beads are mobile and it has been effective.

Question 21

disadvantage of ILA ?

Answer 21

ILA (inhibition of latex beads assay) are time consuming and relies on visual interpretation, Not absolutely quantitative.

Question 22

advantages and disadvantage of RIA ?

Answer 22

RIA (radioimmunoassay) can be easily automated Is easily quantified; it produces radioactive wastes.

Question 23

advantages and disadvantages of dipstick ?

Answer 23

Dipstick is very simple and can be taken at home, it is not quantitative.

Question 24

digital pregnancy test ?

Answer 24

Same test strip inside, but spectrophotometer measures absorbance of test area, a control area and a reference area. A computer program calculates the HCG concentration and displays the appropriate message.

Question 25

digital pregnancy test with time estimate ?

Answer 25

Similar to the digital test but contains 2 test strips optimized for detection of different concentrations of HCG. A computer program uses this information to calculate the HCG concentration and displays the appropriate message including time.

Question 26

problems with measuring HcG ?

Answer 26

HcG can be raised in other rare conditions such as tumors , as well as an incomplete abortion. These are false positives. Is not present in ectopic pregnancy, which is a life threatening condition with no HcG present.

Question 27

how can lateral flow tests also be used ?

Answer 27

Flow tests can be used in microbiology which can test for pathogens, lateral flow tests have also been used in the 2020 pandemic against COVID-19 testing for students travelling to help to contain the spread. However , this is not as accurate as the other tests for detecting viruses , and not as accurate as when used for detecting pregnancy.