Fun With HPT's
or, Dollar Stores Are Dangerous

Ladies, my stick fun, for your enjoyment:

Experiment 1: Urine

Well, naturally, the first thing to do with an HPT is pee on it. In this case, using a cassette test, I peed in a cup and used the enclosed dropper to deposit 4 drops of pee in the "well" as directed. If you read my Cautionary Tale you know I am not pregnant. Sure enough, the test was negative as expected. Here it is, after I disassembled the cassette to get a clear pic:

Incidentally, for a cheapie test, I was impressed-- no evap lines. (And, also incidentally, I purposely photographed the test "upside down" so the control line would be on the left, to match all the other pics on this site.)

Experiment 2: Breastmilk

It has been speculated that breastmilk might be a source of hCG in a pregnant woman who is either currently nursing, or weaned recently enough to be able to express some milk or colostrum. Now, since I am not pregnant, I cannot personally test the theory of when breastmilk would produce a positive HPT (is it a good early test?) or indeed whether breastmilk would reflect a true positive at all.

I can, however, test whether or not breastmilk produces a false positive. Well, more accurately, I can test whether or not breastmilk produces a false positive for me using this brand.

Drumroll please . . .

Negative! However, since milk is thicker than urine (it contains fat, after all!) it did not "wick up" the test quite as smoothly as my urine did, leaving the test a bit pink in the background:

Again, the control line is on the left. You can see how the pink ink collected just a bit on the left.

Here are a couple of pics of the urine and breastmilk tests side by side:

Milk on top, pee on bottom.

In this side view, you can see the streaky ink on the milk (top) test. Also, NO evap lines at all! Note: evap lines are possible with ANY test. I am simply observing that these two didn't have any!

 

Experiment 3: Reusing With Urine And Supplementary Dye

"Can I reuse a test?" is a common question. The answer is no, but that's not a fun answer. So live vicariously. THIS is why you can't reuse a test.

I retrieved HPT #1, the regular old pee test. It had dried by this point. It had no evap line.

There are two problems with reusing the test. The first problem is that all the dye had "crossed" the test. The urine is "wicked" across the test window and carries the dye with it. The dye sticks to the control line (and test line, if pregnancy hormone is detected.) Once the test is performed, there is no dye at the starting point. This part is easily solved using a red ink pen. I colored a thick band near the wick. Now there was ink.

The second problem with reusing the test is NOT easy to solve. The ink doesn't stick unless it has the proper antigens in it. Antigens bind to the control line (and hCG, if it's present, which then stick to the "test" line.) The original dye in the test contains the antigens as well. Once the test is used, those antigens are used up. I do not have a chemistry lab handy, so unlike the ink, which is easy to replace, we hit a brick wall with the antigens.

Just for laughs, however, I ran the test. Here is the reused urine test as it starts out:

Experiment 4: Removing the Original Dye and Using My Own

In this brand (New Choice) the dye/antigen combo is actually a small strip sandwiched into the wick area of the test. For this experiment, I removed that strip (but saved it for later.) Then I added my own red ink in the same manner as my previous experiment. The dye crept across the entire test window successfully, resulting in a blank test:

Not a hint of control line, nor of test line. This is why the control line is important-- if, for some reason, the antigens in your test are not present, the control line won't show up either. That way you don't mistake a "defective" result for a "negative."

 

Experiment 5: Returning the Original Dye and Reusing the Test

I decided to see if this test could be salvaged. I returned the original dye/antigen strip to the wick and dropped another 4 drops of urine in the correct place. It worked!

It took a bit longer for the urine to spread across the window (since it was already wet, it was not "wicked" as quickly as the first go-round) but the control line did appear. This confirms my conclusion: the problem with reusing an HPT is not that the dye is all used up the first time, but that the antigens are all used up the first time.

At this point I decided to photograph my two "artificial dye" tests-- the ones where I had added my own red ink.

As I peered close, I noticed something kind of unusual. Do you see what I saw?

In this picture, more time has elapsed, and the supplemental ink on HPT #1 is slowly spreading across the test. Look at the test line! It's inverted! Apparently the ink not only doesn't bind to the "stuff" there, but it's repelled by it. Once I noticed this on HPT #1 ("Pee"), I peered more closely at HPT #3 ("Dye"). Yup, same thing there, but much lighter. (The difference, to recap: "Pee" was run the normal way and then reused with new ink; "Dye" was run with new ink and then reused the normal way.)

Experiment 6: Breastmilk & the Naked Digital

At this time, I pulled out my Clearblue Easy Digital and decided to disassemble it to see what makes it tick. (The "Anatomy of a Stick" section of this site will be up soon!) Once I pried the case open, I couldn't resist the temptation to use the digital test outside the case. Since I only had 1 test stick left, I decided to combine experiments and use breastmilk to see if it would cause this test to register a false positive.

Despite the absence of the plastic case, the digital display registered appropriately once I inserted the test stick. When I dipped the test in breastmilk, it flashed, indicating it was working. Unfortunately, I then got a "see leaflet" error.

I removed the stick to see what the problem was. To my surprise, there were no lines at all-- the milk had not been "wicked up" the test at all. I was initially surprised-- it had worked on the New Choice HPT, even if it did leave some pink streaks. Then I realized the difference-- before using the digital test I had nursed my daughter, and as soon as she was finished, I squeezed some milk for the digital test. Breastmilk gets thicker as a baby nurses. "Foremilk" is very watery and is the first milk the baby gets. After about 5 minutes of eating, "hindmilk" is released, which contains more lipids and is creamier. Essentially, I used "skim milk" on the first test, and "whole milk" on the second test-- DOH!

Therefore, there were no lines on the digital test strip, and therefore the digital test gave me the error message.

I was determined to salvage something, though! The error message would be on the display for an hour before I could try again, so I put the digital reader aside. I ejected the test strip and dipped it in the milk again, swirling it around, hoping that saturating it would draw more liquid up into the test. It did creep up a bit, but not enough to make it to where the line(s) would be.

So I used my fingers to squeeze the milk up toward the window. It got halfway there, and that was it. I could do no more. However, halfway was enough to register a line! Here is a picture of a digital test strip that worked (in urine)-- it has 2 lines, a "control" line on the right and a very faint second line on the left (probably not even visible in this pic, though it is there.) Below that is the milk test I just used. There is no "control" line because the milk didn't make it far enough up the stick, but there is a "test" line (faint, but there.) The bottom strip has been taken out of its plastic case and looks damaged from the squeezing I had to do, but the blue line is there!)

See the faaaaaaint blue line?

Now, the problem arises: the digital test says to disregard the lines because only the digital display can interpret them. Since the strip ended up becoming so damaged, I couldn't use it in the digital holder after all, so I have no idea if the test would have said "Pregnant" or "Not Pregnant." I do find it interesting that the breastmilk "test" line is darker than my urine test line was . . . but not only did the test fail to absorb/wick the milk, but the lines supposedly don't mean anything anyway. So I'm left with a question mark . . . but am intrigued. If any milk-producing non-preggo wants to waste the money on a digital test and repeat my experiment (with foremilk!!!!!!) let me know how it turns out!

Experiment 7: Breastmilk and the Digital, Part II

After my friend read this section, she decided to repeat my breastmilk experiment. (Her baby is several weeks younger than mine.) She went out and purchased a Clearblue Easy Digital just for the occasion! (Thanks, Karen!) She dipped the test into expressed breastmilk. The digital display read "Not Pregnant." She did, however, find a nice, visible second line on the test stick when she ejected it. (This does NOT mean she is pregnant. She isn't. See the Secret of the Digital section for details.) Here's a pic of her non-pregnant, breastmilk test:

Experiment 8: Breastmilk, Part II

For comparison's sake, Karen also used breastmilk on a non-digital test (in this case, the SmartStrip hCG, purchased through www.testsforless.com.) Surprisingly, she actually did get a faint positive line (this was several weeks ago, and she has not yet had a postpartum period and is definitely not pregnant-- so this is a true false positive.)

Extreeemely faint, but there! Moral of the story: breastmilk should not be used on HPT's if you want an accurate result!

Experiment 9: Blood

Okay, first the big disclaimer. To obtain blood for this experiment, I used a brand new lancet (a diabetic friend had an extra.) This was, therefore, safe and sanitary.

Second disclaimer: when blood tests are done in the lab, they use the serum (clear part) of your blood. I don't have any nifty centrifuges to "spin down" the red cells and separate the serum; I did try several methods for separating them, but none were successful enough to extract the necessary 4 drops for the test. Therefore, I used whole blood, just for the heck of it.

Note: as some readers pointed out to me, a centrifuge is not, strictly speaking, necessary. Leaving whole blood to sit for awhile will cause the red blood cells to separate and sink to the bottom, leaving the clear serum behind. However, in my attempts, I have discovered that in order to obtain enough blood for this, my bloodletting approaches self-mutilation. I'm so not into that. So, I'll stick with my lame finger lancet and whole blood! ;)

Since blood is thicker than water (ha ha) it got "stuck" partway through, and I added a couple drops of water to help it along.

Guess what? I got a faint positive!

The roundish smudge on the right is where the blood originally got "stuck" and started to dry before I added the water drops. See the faint line?

I let the test dry overnight, then added some more water droplets. It cleared the field a bit:

The line seems to be disappearing . . . so my theory is that the red color of the blood merely caught the light the right way (wrong way?!) as it passed over the place where a positive result would be. In other words, a slight line appeared from the presence of the moisture, and the red blood gave it a slight pink color . . . so it wasn't really a false positive. But it's another example of why these tests were really meant for pee only!

On the next day, I added some more drops of water to further clear the blood from the window. It worked:

Now, there still appears to be a very faint line, but I'm still betting on the color of the blood being its cause!

Experiment 10: Urine and Half-Reagent

Sandwiched in the wick end of every HPT is a small little purplish rectangle. This is the dye/antigen combination. I removed this and cut it in half:

I then put one half back inside the test. I dropped some urine on the test in the usual way and got the expected negative result:

I was surprised at how dark the control line appeared, considering I was usingly only half the dye!

Experiment 11: Urine and Half-Reagent, Part II

Then I added the second half of the dye/reagent strip back into the same test and dropped more urine onto it. The result was negative (of course) BUT the second half of the dye crossed the test appropriately and the control line darkened a bit.

Please note: until recently I advocated this as a way to reuse a test. However, I am retracting this suggestion. Though it may work, there is no way to guarantee the integrity of the cellulose (test strip.) It may degrade after being wet and drying again. Rather than risk a confusing result (or worse, a false positive) I think it's best to use a new test.

Experiment 12: Urine

I found another brand of HPT in another dollar store, B-Sure (currently being recalled.)

I peed on it. (Okay, I peed in a cup and dipped ;) Negative . . . but it had quite an evap line! I've used many of these tests and never seen an evap on one yet. However, it was obviously a gray/dent type line and didn't look anything like a true pink positive, so I still consider the test reliable.

Experiment 13: Breastmilk Again

Using a second B-Sure strip, I tried the breastmilk experiment again. Also negative, and also an evap line, but this evap was not nearly as pronounced as the urine version! These tests did come from the same lot, so I found that interesting.

Here are the two B-Sure tests I purchased from the dollar store:

The breastmilk test is on the top, the urine is on the bottom (you can tell the pee test is a bit yellower ;)

I kept both tests and have looked at them occasionally. I actually find the evap lines to be more or less visible in different lights. Natural light makes them most obvious, as pictured above. In the light of my desk lamp at night, however, they're barely visible. Hmmm!

Experiment 14: Saliva

I tried using spit on a test too (another New Choice) and it was terribly boring ;) Negative . . . probably worked just the way plain water would!

Experiment 15: Under-Saturating A Test

I used a test from testsforless.com for this experiment. The directions say to dip the test in a cup of pee for 3 seconds. I dipped for 1 second and got this result:

There was not quite enough urine to spread all the dye across the entire test. However, a control line still appeared, meaning the test is still readable/valid. If you under-saturate a test, you can always add some more urine.

Experiment 16: Over-Saturating A Test

What happens if you put too much pee on a test? Theoretically it's possible. If you truly put too much pee on a test, the control line could be wiped out. However, I discovered it's pretty darn hard to actually render a test invalid with over-saturation.

I took the same (under-saturated) test from above, and dipped it in a cup of pee for a full 2 minutes (remember, recommended time is 3 seconds.) Here's what I got:

A nice, valid control line. I didn't obliterate the test. No false positives. (Incidentally, it is impossible to cause a false positive through over-saturation.)

Well, that was boring. Time for a heavy-duty over-saturation. I stuck the strip back in a cup of pee for another 10 minutes (remember, it had already been dipped for 2!)

Nope. The wick became saturated and stopped "sucking up" the pee. The test area, consequently, began to dry. The line began to dry and faded a bit into the normal dry color. Still very valid and very readable.

So, I think it's safe to say that over-saturation isn't a problem. I highly doubt anyone serious about taking a pregnancy test is going to let it soak for 12 minutes, or 240 times longer than the directions recommend! So if you pee for a few extra seconds, fear not.

Experiment 17: Placing Reagent On Top

The reagent/dye combo is sandwiched at the end of the test. It looks like a purple paper rectangle. I removed it from the test and placed it directly on top of the results window. Then I applied the liquid (breastmilk in this case) directly on top of that.

Because the test is covered with a clear piece of filmy plastic to protect it, it was difficult for the dye/milk to seep down and bind to the antibody strips below, but it did. The result was a very light control line:

Experiment 18: Overheated Test

HPT's are supposed to be stored at room temperature. Heat and cold can affect the chemical reagents and the antibodies that make the test work. So naturally I decided to see if I could screw them up by storing the tests "improperly."

I took a test and cut it in half. One half would be used normally; the other half went into the microwave for 30 seconds. By using two halves of the same test, I could ensure that any variation in the results would be directly attributable to the microwave.

The top half went in the microwave, and the lower half was used normally. Unfortunately my scissors are too dull to make a clean cut, so they look a little battle-scarred . . . but the nuked half still funtioned just fine. A readable control line and no false positives.

Well, that was no fun . . . time for a much more drastic temperature increase. This time I cut a test in half and microwaved one half for a full 5 minutes. This is the result:

Sorry the pic isn't the best, but notice the top (heavily nuked) half has a fainter control line than the unnuked half? A-ha! Success at last. Apparently high temperatures really do damage the antibodies/chemicals. This is why proper storage is important. Alas, HPT's are like batteries . . . when you buy them, you have no way of knowing how long they were on the shelf, or what adverse conditions they may have seen.

Experiment 19: Breastmilk Again Again

I admit that I have conducted more experiments than I have documented here. I have purchased dozens of dollar store HPT's. For Christmas, my friend Karen sent me a big box of tests! So, aside from the more "out-there" stuff I do for this website, I also do lot of random urine and breastmilk tests. It's true that the vast majority of the time my breastmilk does not produce false positives, but once it did. Here it is:

Faint, but definitely there. It appeared within the time limit, and is pink in color. By definition, a true false positive and not an evap line.

This goes to show you that breastmilk is a dynamic fluid. Sometimes there are enzymes and antibodies that cross-react with HPT's. You should not use breastmilk on a urine HPT to diagnose pregnancy!

Experiment 20: Freezing A Test

Piggy-backing on my microwave experiments: I put a test strip (in its foil package) in the freezer overnight. It worked perfectly and turned negative as it was supposed to. However, for all I know, it would have been negative in the presence of hCG, so there's no way to know for sure if it were fully functional. Follow the storage instructions on your tests!

Okay-- had enough Fun With HPT's yet?

Any suggestions? Questions? Comments? Send 'em my way! :D