Week 4 Chapter 48: Home Testing

Pregnancy test accuracy rate

- A pregnancy cannot be detected before implantation. - Because of natural variability in the timing of ovulation, implantation does not necessarily occur before the expected onset of the next menses. - One study found that the highest possible screening sensitivity for an hCG-based pregnancy test conducted on the first day of a missed period is 90% because 10% of women may not have an implanted embryo at that point. - Although most pregnancy tests are advertised as 99% accurate, studies estimate that the highest possible screening sensitivity of a home pregnancy test by 1 week after the first day of the missed period is 97%. - A test sensitivity for hCG of 12.4 mIU/mL is needed to detect 95% of pregnancies on the expected day of a missed period. - The actual accuracy rate of these tests is less because users do not carefully follow the directions; formatting changes and improved instructions could help to improve the patient's ability to use home pregnancy tests and accurately interpret results.

Precautions of HIV-1 Test

- Do not share test lancet with others. Blood being tested should not come in contact with others. - Lancet must be disposed of properly.

What factors does the provider need to keep in mind when determining if HIV-1 test is appropriate for a specific patient to use?

- Elapsed time since possible exposure - Risk factors for contracting HIV - Medical disorders - Physical limitations

Pregnancy test interference

- Miscarriage/birth within 8 weeks (false +) - Concurrent use of Pergonal or Profasi (false +) - Presence of ovarian cysts (false + or -) - Presence of ectopic pregnancy (false + or -) - Test too soon (false -) - Use of cold urine (false -) - Use of wax collection cup (false -) - Soap residue on collection container (false -) - Inaccurate application of sample - Dilute sample - Not following instructions

Patient Education for Pregnancy Tests - Avoidance of Incorrect Results

- Most accurate results obtained by waiting at least 1 week after the date of expected period. Too early may cause false-negative. - Use urine device in kit, don't use waxed cups. - Soap in containers can ruin results. - Test immediately after collection. - If testing later, store sample in fridge, but let it warm to room temp. for 20-30 minute before test. - Do not shake up any sediment in sample.

Who is at risk for contracting HIV-1 virus?

- People who share needles or syringes - Have sexual intercourse with a person infected with HIV, someone who injects drugs, or has multiple partners. - Had a blood transfusion between 1978 and 1985. - Born to a mother infected with HIV.

Usage Guidelines of HIV-1 Test

- Pretest counseling - Clean fingertip - Place a few drops of blood on the blood specimen card. Ensure blood soaked through. - Air dry card for 30 minutes. Seal card in specimen. Return pouch and place in shipping package. Make sure lab receives specimen within 10 days - Call number 3-7 business days after mailing specimen - Counseling

Product selection guidelines

- Some tests as early as the first day of a missed period. - Some tests that detech hCG levels 25/ mlU/mL or less can be uesd 3 days before missed period. - The earlier a test is used, the greater the chance of a false-negative. - Most tests are one-step procedures. - Some tests let you see the reaction occurring, lets you check that the stick absorbed enough urine. - Other tests have two devices and can be helpful if the first test is negative. - New tests show "pregnant" or "not pregnant" or "yes" or "no". - Tests results usually in 3 minutes. - First Response Early Result most sensitive/reliable, detected hCG as low as 6.5 mlU/mL, detected more than 95% of pregnancies on the first day of a missed period.

How do patients obtain HIV-1 test results?

- The test samples are mailed to a laboratory for screening. - Positive samples are confirmed with an immuno-fluorescent assay.

What information needs to be relayed to the patient regarding HIV-1 test results?

- They should be counseled on their results. - If positive, must see PCP immediately.

Patient Education for Pregnancy Tests - Usage Guidelines

- Unless package said otherwise, use urine first thing in morning. - hCG levels the most concentrated. - Check expiration, remove stick right before use, remove cap. - Hold stick in urine stream for designated time on packaging, urinate in testing well of test cassette, or collect urine in collection cup and dip the strip in. (Depends on package) - Lay device on flat surface after, and wait 3-5 minute before reading results. - If negative, test again in 1 week if period does not start.

When can the HIV-1 test be administered?

3 weeks to 6 months may be necessary to develop sufficient antibodies for detection so the time varies.

What do OTC pregnancy tests detect?

Home pregnancy tests detect hCG in the urine.

Patient Education for Pregnancy Tests - When to Seek Medical Attention

If the second test is negative and menstruation has not begun, consult doctor.

Pregnancy test mechanism of action

Mechanism of action - Uses monoclonal or polyclonal antibodies (solid surface/bound to pregnancy stick) in an enzyme immunoassay to detect hCG in the urine. - If urinary hCG is present, it will form a complex with the antibodies. - Another antibody is added, one that is linked to an enzyme and will react with chromogen to produce a distinctive color. - The hCG is sandwiched between the antibody linked to the enzyme and the antibodies bound to the solid surface. - Washing or filtering within the testing device removes unbound substances; a chromogen then reacts with the enzyme, causing a color change.