Bent CGM sensor tip leads to overnight hypo

When I inserted a CGM sensor two days ago allowing an 18-hour pre-soak before the expiration of the current sensor, I should have trusted my gut instinct when it bled more than a small amount.

There’s debate within the community about whether bleeding upon CGM sensor insertion is a dependable indicator of anything. I remember reading on a Facebook forum on this topic. One commenter asserted that blood on insertion is not a bad indication. S/he contended that they thought bleeding was not bad and in fact they thought that, “bleeders are readers.”

Up until this point, my experience taught me with pump cannula sites and CGM sensor sites, bleeding almost always caused me problems. Problems with poor or erratic cannula site absorption and poor or erratic CGM sensor readings.

I tried to keep an open mind upon reading this FB comment. I didn’t want my narrow experience to be the only frame of reference for this important-to-my-health technology. Learning through others experience is important to me.

When I inserted the sensor in question, it started to bleed immediately. I soaked up a fairly large drop of blood near the black round sensor pads. But then it seemed to stop. Now that meme of “bleeders are readers” was in my head and I decided to continue with this sensor.

So, about 18 hours later the new sensor showed a blood stain on the adhesive fabric but it didn’t seem to be overly large. When the old sensor expired, I switched over the transmitter and started a new 10-day session.

During the two-hour blackout period I did five finger-sticks and input the reading into Apple Health in order to keep Loop working. Those finger pokes read: 62, 77, 71, 74 76 mg/dL (3.4, 4.3, 3.9, 4.1, 4.2 mmol/L). I used a small carb correction in response to the 62 (3.4), but felt that the rest of the flat BG data would lead to a great start for this sensor.

When the new sensor data came online, the first three readings could have served as a warning to me: 51, 86, no data (2.8, 4.8, no data). The next four readings continued: 67, 71, 98, 76 (3.7, 3.8, 5.4, 4.2). That jumping to 98 (5.4) and returning to the 70s was volatility that never extinguished until I pulled it in less than a day.

The unreliable sensor led to less than optimal insulin decisions. It did, however, perform one vital function that I am grateful for. It woke me up with a valid 55 urgent alarm. It took me a good 5-10 minutes to muster enough wit to start eating some glucose tabs. One fingerstick confirmed at 44 mg/dL (2.4 mmol/L).

I went back to sleep and decided to deal with the sensor in the morning. First thing I did upon waking was to stop the sensor and insert a new one. When I pulled the offending sensor I made sure to eyeball the sensor wire mostly to notice whether it was there or not.

What I found was a sensor tip bent to a little more than 90 degrees about 1/16" from the tip. This was the cause of my trouble. Not sure how that occurred. I was happy that I decided to pull the plug on this sensor when I did. I only wish that I had written it off right from start when it showed blood.

The lesson that I take from this experience is that my health and safety are far more important than protecting my sensor supplies. As soon as I see more than a little bit of blood I will abort that sensor and move on. I live with the luxury of a generous supply of sensors due to my historical sensor reuse. I am also grateful to live with good insurance coverage.

This morning I inserted a new sensor that did not get the benefit of a pre-soak and it seems to be performing well enough with a few calibrations. Maybe I don’t need to do a 20-hour presoak.

Has anyone else observed a bent sensor tip after removal? Does the appearance of blood when inserting a sensor play any role in your decision making?

Nope, as long as the bleeding stops, I use the sensor with no more issues than if it had not bled. Every couple of years or so, however, I will get a sensor that bleeds so badly that it not only soaks the entire adhesive with blood but also won’t stop dripping blood. I don’t have the patience to wait on those and insert a new one. I presoak most all sensors 24 hours before installing the transmitter so as long as they stop bleeding within 20 minutes or so, I just ignore the blood. I am more concerned about staining clothing than bad BG readings.

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Thanks for the report, @CJ114.

I have been using G6 for 2.5 years or more than 90 sensors.

I have only had one obviously bad insertion which was a total gusher in terms of bleeding, never worked right at all (bouncing between a couple bogus reading but 99% “sensor error wait”) and had a spectacular bruise for most of a week.

I’ve had several more that bled, not too bad, and settled out to be usable, and had a small bruise.

I have never noticed a bent sensor wire. Do you think you hit a rib or something? I always figured a gusher was hitting a vein but that’s just my mental model, not an actual anatomical fact.


From everything I understand about how a CGM works, I really doubt the shape of the filament would have much impact on it’s function at all. Not so long as the filament was intact and conducting. Bad sensors happen, though. I think it’s much more likely that you just got a defective one, evidenced by the bend.

The first time I got a gusher, I freaked out and called tech support, who authorized a replacement. I didn’t read the "bleeders are readers"sentiment until after the fact. On the few other bleeders I’ve had since then, I’ve found this to be true. But in general, I seem to have excellent luck with the G6 sensors. (It’s bad transmitters that seem to haunt me, and they’re a lot more difficult to replace.) I haven’t had a single bleeder since abandoning my abdomen in favor of my arms, though.

The wires do get bent sometimes. When that happens the entire wire doesn’t go inside and so it either is wacky or it drops out before the 10 days.
I’ve had it happen a few times

I’ve had a few bleeders and as long as the skin under the sensor doesn’t feel bruised or tender to the touch then the sensor works fine, however if there is bruising or pain whether bleeding occurred or not then the filament is usually bent and the sensor doesn’t work correctly.

No, I’m certain that I did not hit a rib or some other unusual anatomy. When I think about this, I remember the introducer needle on the G4/G5 sensor. It fully contained the sensor wire within its hollow structure. You would manually insert the needle and then pull back the needle leaving the sensor wire in the tissue below the skin.

One error people could make back then was to pull back on introducer needle prematurely and slightly ahead of the nominal sequence and cause the sensor wire to be damaged.

People would do this because they would wrongly place two fingers under the round plastic collar much like they would place their fingers on the underside of the two plastic tabs on the traditional syringe.

The correct procedure was to push fully on the plunger first, then place two fingers on opposing sides of the round white collar and pull back on the introducer needle.

What I’m thinking is that the G6 insertion device was defective and allowed the introducer needle to be pulled back slightly ahead of time, thereby exposing a short length (about 1/16") of the sensor to contact the skin first and bend before the needle hit and forcibly jammed the assembly below the skin, bent needle and all. Or the sensor wire was misplaced and not fully inserted into the introducer needle.

Not sure that I agree with this. The signal that comes from the sensor to the transmitter is tiny amounts of electrical current generated by the the bi-metal exposure of the sensor tip that’s coated with an enzyme and exposed to interstitial fluid.

Bending this very small wire to a severe angle could change the electrical resistance of that wire and give off erratic electrical current signals that the transmitter would have a hard time translating.

Sorry for the gross bloody picture but it displays the evidence better than my words.

Me, too. In fact, I had one of the best sensor sessions ever in the prior sensor with excellent TIR and the lowest average BG with fewest lows than I’ve ever seen in my data before. It’s as if this was fate’s way of trying to mitigate any undue hubris!

I didn’t have unusual pain or bruising and this persuaded me to hang on longer, a choice that I regret.

The picture helps me a lot, thanks!

As you were pulling sensor off did you notice unusual folding of the sensor wire? Or weren’t really looking?

I can tell you that for me, pulling a sensor off my hairy belly means I’m usually wincing too much to carefully look at the sensor wire.

@Tim12 – No, I didn’t notice the bent filament tip until I pulled off the sensor bandage and then held it up to the light to verify that the filament wire was still there. It’s then that I first noticed the bent tip.

I’ve had that happen only not such a right angle bend. For me the wire is bent because only half went in and the rest bent.
It like like your bent near the top

Yeah, the acute angle of the bend suggests that it bent around a hard surface. The only thing that qualifies in this context is the inside edge of the tip of the hollow introducer needle. The other surface that affected this action was the skin itself. With the high deployment speeds in the G6 applicator, it supplies the force needed to acutely bend this wire. Well, that’s my conjecture.

ANY blood that comes out from my skin seems to cause issues with my sensors, so maybe a couple of times per year. It is incredibly frustrating. Bleeders are NOT readers (for me)!

I’m in your camp, @Allison1. I don’t often have blood show up when I insert a sensor. When it does, sometimes it works OK but often it does not.

I’d rather pull a good sensor too early than stick with a bad sensor too long. The health risks are not worth it to me.

Reading other users above, it doesn’t seem to affect them the same way. This appears to be an issue that varies by individual. For me, bleeders mislead!

Bleeders mislead! I’m so using that one :rofl:

Most likely this happened post removal, because the sensor wire is inserted through a solid tube and the tube is pulled out leaving the sensor in your skin, and when you pull out anything out if your tissue it will drag on the soft tissue and end up fairly straight.

There is the possibility that you pulled out the wire after removing the sensor and it bent when it was pushed back in, I cannot be sure that would cause this.

I have created and duplicated most issues describe online with the sensor insertion by dismantling and reassembling the inserter and the sensor multiple times with ever see a way for the wire to get bent.

I bent a wire once when the device didn’t have complete contact with my skin so didn’t insert correctly. I knew right away that I had just wasted $100.00

I don’t understand this comment. The wire or filament is part of the sensor assembly that includes the transmitter holder. I removed the entire sensor assembly and did not separately do anything to the wire filament.

The sharp angle that the sensor tip is bent does not seem possible to me in an environment of the wire withdrawn from the soft tissue, then pushed back in, then finally withdrawn.

I calculate that I’ve used about 450 Dexcom sensors since September 2009. I’ve never seen this anomaly before and it seems more than coincident that it occurred in the same situation where an unusual amount of blood appeared upon insertion and led to erratic and unstable glucose readings.

I’m ok if this cannot be resolved without a persuasive explanation. Yet, the appearance of more than a small amount of blood upon insertion will constitute a red flag for me (please excuse the pun).

I’ve had my share of bleeders ranging up to blood soaking the G6 adhesive past the plastic. My experience with bleeders is mixed; more than half work (sometimes needing extra time and/or excessive calibrations before getting good readings). Whenever the blood extends beyond or above the holder, the sensor doesn’t work. If I get a questionable one, I’ll pop the transmitter to check.

Dexcom replaces sensors that don’t work or fail due to bleeding with minimal questions.

I’ve also experienced mixed results with sensor insertions that draw blood. The question I ask myself is, why should I take additional time, attention, and risk when blood appears? I’m thinking that calling it quits quickly cuts my losses and gets me on the road sooner to stable and dependable CGM readings.

Since Dexcom is not stingy with replacements, it makes more sense to me to just throw in the towel and move on with my life.