Pregnant but Negative Urine Preg?

  1. Hi all! I'm an ER nurse, and had a pt last noc who swore up and down "there's no way I can be pregnant....my period is 4 days late, but I took a test (urine) this morning and it was negative" The doc wanted to do a serum beta, and lo and behold PREGNANT! Thought I would come to the source and see if any of you guys know how common this is. I've had a couple in the last 6 months (one was a urine preg we did 2 days previous, pt came back and we did a beta).

    Anyone know what the percentage is of women who don't show positive on urine HCGs?
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  2. 44 Comments

  3. by   HairCanada
    usually takes 7-10 days for the urine testto show... could be explanation????
  4. by   tvccrn
    With my third one, I took three HPT's. All turned out negative, including the one I took the morning of a doctor appointment using the same sample of FMU. When the doctor came to talk to me she said she had never seen the line show up so fast in all her career.

    So, yeah, those urine tests can be wrong. Don't know about a percentage however.

    tvccrn
  5. by   BSNtobe2009
    Quote from RunnerRN
    Hi all! I'm an ER nurse, and had a pt last noc who swore up and down "there's no way I can be pregnant....my period is 4 days late, but I took a test (urine) this morning and it was negative" The doc wanted to do a serum beta, and lo and behold PREGNANT! Thought I would come to the source and see if any of you guys know how common this is. I've had a couple in the last 6 months (one was a urine preg we did 2 days previous, pt came back and we did a beta).

    Anyone know what the percentage is of women who don't show positive on urine HCGs?
    I wonder how far along she is....I read somewhere years ago (not sure if it is a myth or not) that a standard pregnancy test will only show up positive for so many months, and after that, it won't.
  6. by   augigi
    What does the package insert say? The manufacturer would have to give the failure rate on there.

    Actually, I looked up the FDA website and it says the "99% accurate" that the packet claims is compared to other tests, not to actual pregnancy!

    The accuracy depends on the level of HCG in the urine, and how well you do the test. Mishandling of the test kit can give inaccurate results.
    Last edit by augigi on Nov 14, '06
  7. by   santhony44
    Quote from BSNtobe2009
    I wonder how far along she is....I read somewhere years ago (not sure if it is a myth or not) that a standard pregnancy test will only show up positive for so many months, and after that, it won't.
    I've seen a urine pregnancy test in a lab show positive two weeks after delivery.
  8. by   cardiacRN2006
    Quote from HairCanada
    usually takes 7-10 days for the urine testto show... could be explanation????
    Not true. HCG will show up in the urine very soon after implantation (can be as early as the next day). Implantation takes 7-10 days after ovulation. Your period can take 12-18 days to come after ovulation. So, a period that's 4 days late has plenty of time to show HCG. But right after implantation it will show up in the urine very soon after. It can be detected around 5 days before a missed period.

    However, HPTs are notorious for having false negatives, and women are notorius for not using them properly.


    To the OP, do you remember the beta numbers?
  9. by   cardiacRN2006
    Quote from santhony44
    I've seen a urine pregnancy test in a lab show positive two weeks after delivery.
    LOL, the HCG doesn't fall out with the baby! It is a chemical that stays around for a while. Women who miscarry (early-like only 5 weeks along) will still have hcg for a while after, and sometimes up to 2 weeks. Your body has to eliminate it!
  10. by   RunnerRN
    Her quant was barely 100.

    Very interesting replies...keep 'em coming!
  11. by   cardiacRN2006
    Quote from RunnerRN
    Her quant was barely 100.

    Very interesting replies...keep 'em coming!

    I'd give my right kidney for a hCG of a hundred!
    Our baseline is less than 5 and HPTs read at the lowest at 25. Some brands like First Response and some ever worse brands read at 100 or more. If she was using a brand like that then she won't show up on it.

    FYI the best and most accurate HPT is the equate at Walmart.....

    POAS ~ HPT FAQ
    (for people who are really interested about HPTs)
    Last edit by cardiacRN2006 on Nov 14, '06 : Reason: link added
  12. by   Gompers
    Quote from cardiacRN2006
    I'd give my right kidney for a hCG of a hundred!
    Our baseline is less than 5 and HPTs read at the lowest at 25. Some brands like First Response and some ever worse brands read at 100 or more. If she was using a brand like that then she won't show up on it.

    FYI the best and most accurate HPT is the equate at Walmart.....

    POAS ~ HPT FAQ
    (for people who are really interested about HPTs)


    Hep, a lot of the store-brand HPTs won't give you a positive unless your HCG is over 100. So if she was barely 100 by blood in the evening, I can see how she'd be under that in the morning. Plus some women don't put enough urine on the test strips or if they drink a ton of water the sample might be diluted...
  13. by   MIA-RN1
    Quote from cardiacRN2006
    LOL, the HCG doesn't fall out with the baby! It is a chemical that stays around for a while. Women who miscarry (early-like only 5 weeks along) will still have hcg for a while after, and sometimes up to 2 weeks. Your body has to eliminate it!
    ?? Doesn't the fact that the HCG stays positive indicate a molar pregnancy or something like that? I thought that the increased HCG after a miscarriage indicates molar and then in turn that the increased HCG can lead to endometrial cancer? I may be confused....
  14. by   babynurselsa
    THe levels will go down slowly over a matter of days to a couple of weeks.

    Another possibility is that if the HCG is very high, beyond what the test can read you will get a neg result. Say the test can read from 100miu-100,000 if her beta quant is 150,000 you would get a neg result.

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