Devices for pregnancy Flashcards
What do pregnancy tests measure?
Human chorionic gonadotropin hCG
What is hCG?
Glycoprotein produced by the trophoblastic cells of the placenta after the ovum has been fertilized and implanted in the uterus
How do the pregnancy tests chemical reaction work?
- hCG comes in contact with monoclonal hCG antibodies that are labeled with detection molecules
- (colloidal gold, latex beads)
- hCG-antibody complex migrates by capillary force onto specific analyte capture zones, forming a visible line
When do hCG levels become detectable?
What rate do the levels go up by?
What days do they peak?
When do they return to baseline?
When do hCG levels become detectable?
- 10-12 days after fertilization
What rate do the levels go up by?
- doubles every 2-3 days
What days do they peak?
- Day 60-70
When do they return to baseline?
- 10 days after birth
Where do the excess buffer along with reagents that are not captured at test control line move onto?
The absorbent wicking pad
What is the lateral flow technology membrane made of?
Nitrocellulose membrane
What is the sensitivity of a pregnancy test dependant on? (2)
Timing of test
Detection level of the test
What is the detection level for most pregnancy tests?
25-50 IU/L
As you get closer to menses, does accuracy of pregnancy test increase or decrease? How many days before the expected period can you test?
increase
- 0-4 days before
What are causes of false positive during pregnancy tests? (5)
- Fertility drugs
- Ectopic production
- Conducting the test after missed or incomplete abortion
- Early pregnancy loss (miscarriage)
- low levels of hCG produced by pituitary during LH surge in menopausal women
What are causes of false negatives during pregnancy tests? (2)
- Testing too early after conception
- Human error
What are important counselling points for instructions of use? How are results read?
Pee for 5 seconds
place pointing down for 20 seconds, lay flat
will see results in 3 min
Not pregnant, Pregnant 1-2 weeks etc.
What do ovulation tests measure? How long does ovulation last
LH surge
- occurs 24-36 hours before ovulation
- have 2 days to maximize chances
How is clearblue advanced ovulation test different than the regular one?
Measures estrogen rise as well
- increases 1-5 days prior to ovulation
How do urine drug screening tests work? I.e What happens when presence of drug
- Lateral flow technology
- COMPETITIVE binding
- Presence of drug leads to missing band
Do you have to confirm drug tests? Using what?
Yes,
- using gas chromotraphy/mass spectrometry
How does the drug test competitive format work?
The drug of interest competes with the binding of the detection molecules to the capture molecules
- Detection molecules: antibodies conjugated with latex or gold particles
Since detection molecules cannot bind to capture molecules (since it is on the drug), no line is produced
What do the positive, negative, invalid results show?
Positive: 1 line on CONTROL (C)
Negative: 2 lines
Invalid: 1 line on Test line
What are reasons for false positives? (1)
Possible cross-reactivity with other drugs or foods
- doxylamine causes false positive
What are reason for false negatives (6)
- Urine sample collected before drug was present in urine
- urine sample after the drug is no longer in urine
- drug used is not one detected by device
- Adulteration of urine sample with bleach
- Sample was diluted with other liquids below level of detection
- Drinking large amounts of water
What do the adulterants test for? (4)
- Tests for presence of oxidants
- bleach or peroxide - Specific gravity. 1.003-1.030
- ensure sample is not diluted - pH normal 4-9
- for acidic or alkaline adulterants - Temperature strip
- ensure sample is fresh
Which vaginal infections can you self-treat? Which can you not?
Self-treat
- yeast
Rx
- bacterial vaginosis
- trichomonal infections
What are symptoms of vaginal infections for when to use the test? (3)
- itching or burning
- excessive discharge
- abnormal discharge colour or odour
What do vaginal tests measure?
pH
What are normal pH vs elevated vaginal pH?
Normal: 3.8-4.5
High: over 4.5
Why is vaginal pH measured? What is it used for?
Used for differential diagnosis
- over 4.5 means it is likely a bacterial infection needing referral
- if test is normal (negative result) consider OTC antifungals
When can the vaginal test NOT be used
Not if +/- 1 day of period
Not if signs of menstruation or signs of any vaginal bleeding
Not if less than 12 hours after sexual intercourse or vaginal douching
Not for STI (HIV, chlamydia, herpes, gonorrhea, syphilis)
Not until 72 hours after the application of vaginal preparations (like contraceptive creams or lubricants)
What are important instructions for the test?
Insert yellow tip into vagina until your fingers reach the outer skin & ROTATE
- 5cm in
Wait 10 seconds for tip colour changes
How to interpret results for vaginal testing?
Positive: tip turns blue/green
- pH high
- could be bacterial
Negative: tip stays yellow
- low risk of infection
- can use OTC products
