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HPT FAQ
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Questions
1. How soon can I test?
2. What's the best test to use?
3. Can I reuse a test?
4. Pretty please?
5. Can I still be pregnant if the test is negative (have a "false negative")?
6. Could I have a false positive?
7. What's an evaporation line?
8. The positive line is really faint. Is this okay?
9. I took another test and the line is lighter. Does this mean anything? Should it get darker?
10. I took several tests and got both negatives and positives. What gives?
11. Hey, I got a positive test but my period started anyway! Huh?
12. The line appeared after the 10-minute time limit. Is it still positive?
13. The line disappeared after the time limit! Is it still positive?
14. Will I get a positive test at the same DPO as I did in my last pregnancy?
15. Do I have to test with my first morning urine (FMU)?
16. What are the different types of tests, and how do they work?
17. What's the deal with "the rabbit dying"?
18. My period is really late, but my HPT's are still negative. What's up?
19. Do evaporation lines disappear?
20. Which tests are more sensitive, ones that measure smaller or larger amounts of hCG?
21. How much hCG should be in my urine during early pregnancy?
22. My digital test said "Not Pregnant," but the test stick has 2 lines. Am I really pregnant?
23. Can using too much or too little pee affect the results?
24. Can I use Clear Plan Fertility Monitor sticks in the digital HPT (or vice versa)?
25. My HPT was positive, but the urine test at my doctor's was negative. Huh?
26. My test developed a line, but it's going the wrong way. Or it's in the wrong place. Or it's the wrong color. Is it positive?
27. How long after implantation bleeding can I expect a positive pregnancy test?
28. Will my urine look different if I'm pregnant?
29. Is it better to pee directly on the test, or dip it in a cup of pee?
30. My blood test was negative. Can I still be pregnant?
31. Can I use an expired test?
32. I've heard "a line is a line"-- any line is a positive. Is that true?
33. I read online that I can pee on dandelion leaves and they will develop red blisters if I'm pregnant. Is this true?
34. I'm breastfeeding. Can that affect my pregnancy test results?
35. Can I get a false positive if my pregnancy test touches my ovulation test?
36. Should I take my test apart to see the line(s) more clearly?
37. Can I still use pee that's been sitting in a cup for several hours?
38. I smoked some pot, drank a lot of beer, took Advil, am on the Pill, had sex, and had Chinese food for dinner. Can that affect my test results?
39. I am trying to conceive through in vitro fertilization (IVF.) Will my medications affect how or if I can use an HPT?
40. The directions on my HPT say "for in vitro use only." What does that mean?
41. Will HPT's stop working after a certain point in pregnancy?
42. I used a digital test and the window said "See leaflet." What does this mean?
43. I used a test with a +/- results window. The horizontal (-) line is very faint, is that okay?
44. How long does it take synthetic hCG (trigger shot) to leave my body before I can test for pregnancy?
45. How long will the words "Pregnant" or "Not Pregnant" be displayed on my digital test? Can I retrieve them later to show somebody?
46. My question isn't answered above. Can I ask you?
Answers
1. How soon can I test? Well, first you gotta know how the test works. Briefly: the home pregnancy test (HPT) works by detecting a hormone called human chorionic gonadotropin (hCG.) When an egg is fertilized, it takes about 6 to 12 days to implant in the uterus, and then it begins to secrete hCG. It takes another day or two for enough hCG to build up and make its way into your pee. So, generally speaking, the earliest you can expect a positive HPT is 8 days past ovulation ("DPO") and the latest would be about 16 DPO. It is possible to get a positive test earlier or later, but not as common. In my experience, if you use a sensitive "early" test (anything that detects 25 mIU/mL of hCG or less) you can test around 12-14 DPO and feel reasonably secure with your results (the later you test, the more secure you can feel in its accuracy.)
If you do not chart or monitor your fertility in any way, and you think you may have conceived, you should wait 19 days (or longer) after having sex to test. Why 19?! Sperm can live approximately 5 days in the proper environment; if the sperm managed to live until you popped an egg, the actual conception could have taken place several days after the sex act that got the sperm there. To make sure you're not testing too early, assume the sperm had very long lives (5 days is considered a very long sperm life) and that conception occurred then. Then allow 14 days for the embryo to implant and develop enough hCG to show up on a pregnancy test (96% of pregnant women will test positive by then.)
Note: some HPT's say "test 5 days before your period is due!" or some such thing. Please note they are assuming a textbook 28-day cycle, with ovulation on Day 14. "5 days before your period is due" thus really "translates" to 10 DPO.
Essentially, you should remember that your high school biology textbook was WRONG. NOT all women have 28-day cycles and NOT all women ovulate on Day 14. For more info on this type of thing, see the Fertility Info section.
Here's an example. This is the textbook-perfect 28-day cycle with ovulation occurring on day 14 (in pink.) 10 DPO and later are reasonable days for testing (in green.) This is the cycle the HPT companies have in mind when they say "test 5 days before your period is due!"
Well, not everyone's body works this way. Here's another 28-day cycle-- but this one has ovulation occurring a little bit later, still well within the normal range. Watch what happens to your (green) testing opportunities!
All of a sudden, "5 days before your period is due!" is way too early for you to expect a positive test! (I tend to ovulate later myself, so by the time the "gold standard" of testing at 14 DPO is applicable, my period is already 3 days late! I needed to use an "early detection" test on the first day of my missed period. A "regular" test would probably have been negative-- even though my daughter is living proof that I was, indeed, pregnant ;)
Of course, it works in reverse, too. If you're an early ovulator, you're lucky! Check it out:
In this scenario, you could test even sooner than 5 days before your expected period.
Ultimately, it's important to remember that implantation is a variable thing. You may be able to detect a pregnancy very early on, but then again, you may not! If you can't, don't despair.
2. What's the best test to use? This seems to change periodically! Some tests are well-liked and then a "bad batch" comes out, and some tests are known for being duds but then switch manufacturers and redeem themselves. See the HPT Overview section for current comments on each brand.
If you are trying to detect a pregnancy 13 DPO or earlier, you probably want to use a more sensitive brand. Anything that detects 25 mIU/mL of hCG (English: anything that detects a tiny bit of pregnancy hormone) is good for early testing. See the HPT Overview section to see which tests are most sensitive and the HPT Showdown for a real-life comparison of 15 brands.
Surprisingly, cheap tests purchased at dollar stores or on the Internet are often more sensitive and reliable than expensive store brands. HPT's are like soda: very cheap to make, and marked up quite a bit for retail.
3. Can I reuse a test? No.
4. Pretty please? No! It just plain won't work. (You could try, but the results would not be reliable.) Note: until recently I advocated cutting a test strip in half lengthwise to make one test into 2. I am retracting this suggestion because of several reports of false positives using this method.
The reason you can't reuse a test is because the dye/reagent combo is completely used up the first time. If you look at the pink dye near the wick, you will see that it passes across the stick when it's used. If you use the test a second time, there are simply no chemical reagents or dye left in the test. Even if you add dye with a marker or pen, there is no reagent left to bind with hCG (if it's present.)
To prove it, I took some pure hCG (thanks SO much to my friend, who had some left over following some hormonal treatment!) and put 3 drops straight on a pregnancy test (the "control" test.) Then I put 3 drops on a (negative) test I had once used with breastmilk; I also put 3 drops on a (negative) test I had once used with urine. Here are the results ("control" lines are on the right):
You can see that pure hCG, used on a brand new test, resulted in a positive test. The same amount of pure hCG, reused on a breastmilk test and a pee test, resulted in negative tests. There were simply no chemicals or dye left to work.
Also check out the Fun With HPT's section for an experiment involving test reusage and adding artificial dye.
5. Can I still be pregnant if the test is negative (have a "false negative")? In a word, yes. You could be testing too early (before your baby is making enough pregnancy hormone to be detected by the test.) And some women (this is fairly rare, but possible) never get a positive urine test even when they're definitely pregnant (for some reason the hormone doesn't make it into their urine.) I have a friend who didn't get a positive HPT until 25 DPO! (With her second baby, a test at 23 DPO was negative . . . but a test on 30 DPO was positive. Oddly enough, with #3, her positive test came at only 12 DPO.) If you get a negative test but think you might be preggo anyway, wait a couple of days (giving the hCG hormone time to build up) and try again. It's not over until the fat lady sings-- and your period crashes the party.
If you are not monitoring your fertility in any way (OPK's, charting cervical mucus or basal temperature, ultrasounds) it becomes extra-tricky. There are two parts to every menstrual cycle: from the start of your period to ovulation, which can vary quite a bit in length, and from ovulation to your next period, which is usually consistent in length. (This second half is known as the "luteal phase," and the normal range is 10-16 days. It's normal for your typical luteal phase to vary by a day or two. For example, mine is normally 11 days, but 10 and 12 are not unheard of either. I have also had a couple of longer ones by total fluke.)
Because ovulation can happen at any time, it's possible your egg was delayed for some reason (stress, illness, travel, excitement.) This doesn't mean your period is actually "late" (it could arrive within the normal 10-16 days after ovulation), but rather than your entire cycle was delayed due to a later-than-usual ovulation.
6. Could I have a false positive? Check out The Truth About False Positives for an in-depth look at false positives. Essentially, it is possible, but it's unlikely. If you get two lines, you're most likely pregnant. Exceptions: if you have been taking certain fertility meds with hCG, the test may be picking up the hCG from the meds and not an embryo. Also, some tests develop "positive" lines after the time limit. You should NOT read the test after the time limit (usually 10 minutes, but check the directions that came with the test.) Yes, this means you should throw the test away and NOT dig it out of the trash in three hours to see if a line magically appeared. And, if the "positive" line is gray or looks like a "dent" in the test, it is an evaporation line and not a true positive.
Lastly, if you have been pregnant recently, it's possible that the test is detecting residual hCG. However, if a pregnancy ends early on, it's unlikely that hCG will remain in your system very long, so most women have nothing to worry about here. (It's extremely common for women to conceive immediately following an early miscarriage; the body is "primed" for pregnancy, so to speak, and elevated progesterone left from the miscarriage gives the next embryo a great shot at a healthy implantation. So, most women really are detecting a new pregnancy.)
However, the more hCG you had in your system when the pregnancy ended, the longer it will take to dissipate. HPT's can even detect residual hCG for up to 6 weeks following a full-term birth. It's a possibility you should keep in mind if you get positive HPT results soon after a previous pregnancy ended.
Check the HPT Overview page for up-to-date comments on various brands.
7. What's an evaporation line? Evaporation ("evap") lines result with the test's antibody strip just looks slightly different than the space around it. There is a line of antibodies (usually made from mouse cells) in the Control and Test section. The Control line binds with any liquid and turns pink (or blue, in tests using blue dye.) The Test/Result line turns pink only if pregnancy hormone is detected. If not, the moisture passes over this strip and does not turn pink. It may, however, become more visible when the light hits the moisture on the strip-- it may appear gray, colorless, like a "dent" in the test, or like a "ghost line." It may appear at any time-- as soon as the urine hits it, after a few minutes as the test absorbs the moisture, or after the 10-minute time limit. It may appear when the test is drying, or after it has dried. It may disappear as the test is drying, or after the test has dried, or not disappear at all.
The simple fact is that there is always "something there" that is slightly visible-- it's simply the antibodies on the test that would turn pink in the presence of hCG. When the test becomes wet, or as it dries, or after it dries, the antibody strip may become more visible. Therefore, all tests may have them. It is not a defect; it's just how tests are made.
A real positive is identified by its color (pink or blue, whatever the color of the test's dye is) and its appearance within 10 minutes of urinating on the stick. A line that appears after 10 minutes, regardless of color, must be considered an evap line and is caused by the test's chemicals changing. HPT's are rapid assay diagnostics, which means any results appearing after the "rapid" time limit of 10 minutes are invalid.
8. The positive line is really faint. Is this okay? An HPT tells you exactly one thing: your urine either has detectable pregnancy hormone in it, or it doesn't. The darkness or lightness of a line doesn't mean much. Generally speaking, a very light line can mean there is a small amount of hCG in your urine, and a very dark line can mean there is a larger amount of hCG in your urine. This is why you may get a faint positive at 10 DPO but a darker positive at 18 DPO. However, this is not always true. Tests are all different, and even tests in the same box may differ in sensitivity. Comparing light/dark lines will just drive you nuts. If you see a line in the "results" window, you're preg!
9. I took another test and the line is lighter. Does this mean anything? Should it get darker? Not necessarily. In general, the positive line will be darker when a greater amount of hCG is present in the urine, but not always. Some tests contain more or less dye (meaning there is just more or less color to "stick" to your hCG.) Some tests are more or less sensitive-- even 2 tests in the same box can be different. Also, your urine may have more or less hCG in it depending on what you ate or drank, or how long it's been since you last peed. Food itself does not cause false results, but can affect how much urine you have and how dilute it is. Eating salty chips and drinking caffeine all day will result in more concentrated pee, whereas gorging on watermelon and ginger ale will result in lots of very dilute pee. But an HPT is not meant to tell you "how" pregnant you are. It only tells you if you are pregnant or not. As long as there is a line in the results window, you are pregnant.
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