How to confirm hypoglycemia with a meter and a sensor

Yes, if you can do it in less than a minute. A meter test shows you how low your glucose is and helps you choose the right amount of carbohydrates [1]. The rule does have one clear limit. If the device is not within reach and you have symptoms, you treat right away and measure afterwards.

The risk of taking 15 g of glucose without needing it is small. The risk of waiting 5 extra minutes during a rapid fall in glucose is far greater. There is one situation in which you do not measure at all, when the patient is not conscious or cannot swallow. In that situation no time is lost on the meter, but nothing is given by mouth either. Glucagon is given and help is called [1].

You treat as if it were hypoglycemia. You take fast-absorbing carbohydrates, stop what you were doing and wait 15 minutes [2]. It is the only correct decision when you have no way of confirming.

The consequences of the two possible mistakes are not equal. If you treated for nothing, your glucose will rise a little for a short while. If you did not treat a real hypoglycemia with carbohydrates you can end up with a severe episode [2]. That is why a borderline situation is always settled in favor of treatment, and the final conclusion is drawn later, once you have access to a glucose meter.

No, and that does not mean a fault. The meter measures glucose in a drop of blood. The sensor measures the glucose concentration in the fluid between the cells, in the tissue under the skin. They are two different fluids, connected to each other but not identical.

The values are normally close, and the difference does not matter much for everyday routine decisions [3] [4]. The difference between the devices becomes important when glucose is changing fast, up or down. In those moments the two devices correctly show two different points on the same glucose curve.

Glucose needs a few minutes to move from blood into the fluid between the cells. In patients with type 1 diabetes the lag has a median value of about 7 minutes and sometimes reaches 10 minutes [5]. On top of this physiological lag comes the device's calculation time. The displayed value can lag behind by 5 to 15 minutes.

The consequence shows up exactly when it matters. During a rapid fall in glucose the sensor displays a higher value than blood, so remember that you are lower than the screen shows. After correcting, the opposite happens, because blood rises first and the sensor follows with the same lag. Do not eat a second time just because the sensor has not moved enough yet, as the figure below shows.

Confirming with the meter remains necessary in four situations, in which the value on the sensor is not enough:

• Symptoms that do not match — you feel low, but the number on the screen is normal;
• The first day of a new sensor — accuracy is lower at the start of wear;
• Right after correcting hypoglycemia — blood rises ahead of the fluid between the cells;
• Before an important decision — a larger insulin dose than usual or getting behind the wheel.

Otherwise the sensor is enough for everyday decisions, and current devices are accurate enough to be used on their own (non-adjunctive sensor) [4] [6]. A meter with strips that are in date must nevertheless be within reach at home and in the bag you travel with. A sensor can come off, can stop or can give wrong values on exactly the day you need it.

It is the low value you see on the graph in the morning, without having felt anything overnight. It is called compression hypoglycemia and it happens when you sleep on the sensor. Pressure reduces the circulation in that area, so the amount of glucose reaching it falls, even though the glucose in your blood is normal.

The pattern is fairly characteristic, with a sudden fall, a flat line for a few tens of minutes and an equally sudden recovery when you turn onto your other side. The official name for this sensor behavior is NSA (Nocturnal Sensor Attenuation) [7]. If a sensor alarm wakes you at night, measure with the meter first, before eating anything [4]. An unnecessary meal at night has a high glucose in the morning as its consequence.

Yes, sometimes even more than the value itself. The arrow shows you the direction and the speed. A steady glucose of 80 mg/dL (4.4 mmol/L) calls for nothing on the spot. The same value with the arrow pointing down, an hour after a meal, means you will be below the hypoglycemia threshold within minutes. Active insulin will keep pushing your glucose down.

Use the arrow to act earlier, when that is warranted. It does not mean the same thing in every patient and depends a great deal on the active insulin in the body. Rules for adjusting insulin doses by the arrows do exist, but they are set individually, with your doctor [8].

You go by the meter and by how you feel [4]. Wash your hands, repeat the test with a fresh drop of blood and treat according to the result. A large difference at a single moment is often explained by a rapid fall or a rapid rise.

If the difference repeats in steady moments as well, the problem is with the sensor. Check whether it has come off and whether the area is irritated. On models that allow it, calibrate. A sensor that is consistently too low causes alarms and unnecessary extra meals. One that is too high is more dangerous, though, because it can hide hypoglycemia.

Yes, and the error goes in a direction that matters. Traces of sugar on the fingers, especially after peeling a fruit, give a falsely high value. After peeling an orange, a kiwi or some grapes, the values measured with the meter without washing are higher than the real ones [9].

Wiping with alcohol does not solve the problem, not even repeated a few times, while washing with water solves it completely [9]. The danger is directly linked to hypoglycemia, because a falsely higher value can make you believe you are safe exactly when you are low. Wash your hands with water and dry them before every meter test.

Every 15 minutes after each correction with carbohydrates, until you get above 70 mg/dL (3.9 mmol/L) [1]. Do not measure more often, because carbohydrates need that time to be absorbed. A test after 5 minutes frightens you for nothing without telling you anything new.

Once you are out of hypoglycemia, check again after about an hour, especially if rapid insulin is still active. If you look at the sensor, remember that it lags behind and will show the rise in glucose somewhat later. For this interval the meter is the more suitable device.