Impact of Squeezing Condition to Obtain Sufficient Blood Volume for Self-Monitoring of Blood Glucose Using an Automatic Puncturing and Sampling System

Abstract

Blood sampling for self-monitoring of blood glucose is difficult for the elderly with low dexterity. We developed and tested the utility of an automatic puncturing and sampling (APS) system as a part of an automatic SMBG device, but success rates of securing sufficient blood volume was low (61.9%). Thus, the squeezing condition was changed to increase its success rate. The aim of this study is to investigate the impact to the amount of bleeding by making changes to the squeezing condition. In our previous experiment, blood sampling was performed simultaneously with squeezing, whereas the present study tested blood sampling after squeezing. This method increased the success rate (75%) among eight subjects who had a low success rate (25%) in the previous experiment using the APS system.

Diabetes is common in the elderly due to decreasing glucose tolerance with aging.^1-3 Self-monitoring of blood glucose (SMBG) is effective for blood glucose control. ⁴ However, conventional SMBG processes are cumbersome and it have been produced difficulty among the older people with low dexterity when they use it.^5,6 An all-in-one SMBG device that can puncture, obtain the blood sample, and measure blood glucose levels can simplify SMBG for them.

One challenge has been that all-in-one SMBG devices previously available could not secure sufficient blood volume automatically. ⁷ The all-in-one SMBG device the POGO® currently on the market which has very simple step, but it requires that patients squeeze the puncture site if sufficient blood volume cannot be secured automatically. ⁸ So, it cannot say to appropriate for all the older people. Securing sufficient blood volume is an essential point for an all-in-one SMBG device.

We reported previously on the development of an automatic puncturing and sampling (APS) system (T-ANTBGM 1 TERUMO Co, Tokyo, Japan) as part of an all-in-one type SMBG device. ⁹ The device punctured, squeezed, and sampled blood automatically using an approved lancet and a sensor tip for SMBG testing. Also it has confirmed that obtaining the blood drop into a strip is easy using the APS system if there was enough blood volume.

The success rate for obtaining sufficient blood volume (0.8 µL) was 61.9% (49% in males, 68.9% in females) in 140 healthy volunteers. Factors affecting puncture failure were gender, large finger diameter, and thick finger pad; a factor affecting squeezing failure was lower peripheral skin temperature. The APS system is required improvement as the above results was lower success rate than expectation.

Certainly, deeper puncturing resolves the above-mentioned puncturing failure factors and would increase success rates. However, puncturing should be minimized because patients with diabetes are vulnerable to infection and wound-healing problems.^10,11 To solve the squeezing failure factor, it is possible to add a mechanism to warm the fingers, but patients with diabetes often have peripheral neurological disorders, ¹² presenting a risk for burn injury. Therefore, to increase success rates, we changed the squeezing condition by shifting the timing of squeezing and sampling, which were performed simultaneously in the previous experiment. The aim of this report is to investigate the impact on success rates in securing sufficient blood volume for SMBG testing by changing the squeezing condition of the APS system. Furthermore, we investigated whether success rates changed for male in this study, as the success rate for males was low in the previous study.

Methods

Subjects and Targets

Subjects were selected by snowball sampling. They were 8 healthy adult male volunteers who experienced difficulty in obtaining sufficient blood volume using previous APS procedures. Exclusion criteria included subjects with deformed or scarred fingers. The trial was performed two times on different fingers per subjects. The two target fingers were selected randomly from the second, third, and fourth fingers of both hands.

Difficulty was determined when the subject was unable to obtain sufficient blood volume for SMBG testing on the first try using the APS system. In previous procedure, four subjects obtained sufficient blood volume on the second attempt, and other 4 subjects were unable to obtain sufficient blood volume on the second attempt too. The success rate was 25% (4/16) using the previous procedure.

Protocol

The APS system automatically punctures the skin and squeezes out the blood for SMBG testing. The system carries out these two functions using two motors. Target sites for this device are the finger pads (ie, the palmar surface of the fingers) (Figure 1).

Steps for this procedure are as follows:

1. Pressing the start button, after a subject places the finger pad down on the device.

2. The cylindrical pressure part rises from the bottom and applies a pressure of 14.7 N to the finger pad for 5 seconds for reactive hyperemia before puncturing.

3. The lancet (Medisafe® Fine Touch® Dispo, TERUMO Co, Japan) rises from the bottom and punctures the finger pad automatically. The lancet that could puncture skin instantly with an applied force of 4.9 N was selected.

4. The cylindrical pressure part rises from the bottom and applies a pressure of 14.7 N around the puncture site for 5 seconds, the strip (Medisafe FIT®; TERUMO Co, Japan) sampling blood simultaneously. At that time, the tip of the strip is in close contact with the puncture hole. This step of applying pressure around the puncture site and sampling the blood is performed two times. If the blood volume obtained is >0.8 µL, the blood soak in a built-in filter of the strip and confirmed macroscopically from the back side of the strip.

Figure 1.

Structure of APS system. A lancet is put under a finger pad. Motor 1 transversally slides finger station, including a lancet and cylindrical squeezing part. Motor 2 applies longitudinal pressure to a lancet and cylindrical squeezing part from bottom. The current study was performed without a strip.

Procedures for the current study are as follows: The steps before blood sampling are same as those in the previous study (above-mentioned Steps 1-3). In this study, Step 4 is performed without a strip. A researcher performs blood sampling by capillary action using a glass capillary (0.6 × 0.3 × 120 mm; external diameter × inner diameter × length: Microtube® Nippon Electric Glass Co, Ltd, Japan), and calculates blood volume (0.15 × 0.15 × 3.14 × length of sampling blood = X µL) to determine whether sufficient blood volume for SMBG testing is obtained. If the blood volume obtained is <0.8 µL, a researcher squeezes the punctured area manually using a cylindrical pressure device ¹² and confirms whether additional bleeding is produced. The manual cylindrical pressure device can provide a pressure of 14.7 N manually as with the APS system.

Ethical Considerations

This study protocol was approved by the Research Ethics Committee of the University of Tokyo (#11366-1).

Results

Eight adult male subjects participated in this study. The success rate was 75% (12/16), in subjects who experienced difficulty in obtaining sufficient blood volume by way of simultaneous squeezing and blood sampling (Table 1).

Table 1.

Results of Obtained Blood Volume.

ID	Age	Previous experiment	This experiment
		Blood sampling at the same time as squeezing	Blood sampling after squeezing (μL)	Additional bleeding after manual squeezing (μL)
1	28	–	7.91	–
		–	4.31	–
2	59	–	0.07 a	0.00
		>0.8	0.21 a	1.70
3	41	–	5.86	–
		–	0.92	–
4	43	–	2.12	–
		>0.8	5.16	–
5	35	–	1.98	–
		–	0.64 a	0.49
6	48	–	1.13	–
		–	3.32	–
7	42	–	0.00 a	0.00
		>0.8	1.13	–
8	46	–	3.39	–
		>0.8	4.66	–
Mean(SD)	42.8 (8.5)		2.67 (2.29)
Success rate of securing necessary blood volume (0.8 μL)		4/16	12/16
		(25%)	(75%)

a

Less than necessary blood volume for SMBG testing (0.8 μL).

The mean amount of bleeding was 2.67 (0.00-7.91) µL. Four subjects produced inadequate blood volume. One of them produced no blood at all. The subject who had no bleeding reported no puncture pain, but the lancet had worked. The other 3 subjects produced bleeding, but the volume was insufficient for SMBG testing. Two of the above 4 subjects who had produced inadequate blood volume produced sufficient additional bleeding by manual squeezing; the other 2 subjects produced no additional bleeding, even with manual squeezing.

Discussion

The success rate for obtaining sufficient blood volume for SMBG testing was 75% in this study by changing the squeezing condition. The success rate increased 50.0 points compared with the previous method in the same subjects. In this experiment, a glass capillary was used for blood sampling, but the sensor tip used in the previous study had a capillary, so both studies are the same in terms of blood sampling using capillary action. In the previous procedure, the sensor tip made contact with the puncture hole, and blood sampling was performed simultaneously with squeezing. The primary point of difference between this study and the previous study were the squeezing condition and blood sampling timing.

We have reported that 0.8 μL or more of blood was obtained in 100% of cases from finger pads in the elderly, as follows. ¹³ In the previous study, the circumference of the puncture hole was pressed manually with a pressure of 14.7 N, two times for 5 seconds each, using a cylindrical pressure device, after puncturing with a lancet, which is consistent with the current study. Also, in the previous study, blood sampling was conducted using a glass capillary after squeezing. Thus, the squeezing condition in both the previous and current studies were equivalent, which the area of the puncture did not come in contact with anything during squeezing. In other words, squeezing was performed without resistance at the puncture site.

Invasion from puncturing is minimal, because we used a 30-G, 0.8-mm lancet. Furthermore, blood pressure of the capillary is very low. ¹⁴ Hence, there are few cases of obtain sufficient bleeding for SMBG testing by only puncturing. It is possible that the squeezing condition has a significant effect on the amount of bleeding produced.

Because the APS system is designed so that the position aberration between the puncture site and where the sensor tip contacts the skin is 0.7 mm or less, it is possible that the tip of the sensor with a diameter of 1.5 mm contacts the puncture hole, producing resistance to bleeding at the time of squeezing. This may be explain the small volume of blood obtained when sampling is performed at the same time of squeezing.

Using this blood sampling procedure, even in cases where obtaining sufficient blood volume for SMBG testing proved difficult, the success rate for the APS system have been improved to 75%. Further improvement is necessary in the clinical setting, but the result of this study suggests that it is feasible to sample blood using the APS system. Four subjects couldn’t produce sufficient blood volume: 1 subject produced no bleeding at all, and the other 3 subjects produced insufficient blood volume. Regarding the subject who produced no bleeding even after manual squeezing following automatic puncturing and squeezing, there was a possibility that the needle length was insufficient for his stratum corneum thickness. Meanwhile, in cases where sufficient blood volume could be produced by manual squeezing after the test, additional measures, such as the modification of pressure force or angle, improved the chances of successfully securing a sufficient blood sample. Because their puncture hole was sufficient to produce bleeding.

Conclusion

We found that the squeezing condition improves success rates in obtaining sufficient blood volume for SMBG testing using the APS system. Blood sampling after squeezing raised the success rate by 50.0 points compared to the method of blood sampling and squeezing simultaneously.