Vol. 25 • Issue 5 • Page 26
There is no doubt that point of care testing (POCT) will grow-not only in hospitals, clinics and single physician’s offices, but also in homes of patients with diabetes and other chronic diseases. There are many advantages to this approach to monitor and even diagnosis diseases in real time at the patient’s bedside. However, with this technology comes varied challenges.
Inoue et al.1 reviewed 11 studies comparing the accuracy of blood-glucose measurements with blood gas analyzers and POCT devices, using arterial blood as the specimen type for both techniques. The blood gas analyzer results were significantly higher than those measurements using POCT. Furthermore, in the hypoglycemic range (less than 81 mg/dl), the incidence of errors using the POCT was even higher. Other sources of POCT errors on accuracy of glucose results were unstable hemodynamics (edema and use of a vasopressor) or use of insulin.
“Because blood-glucose monitoring was less accurate within or near the hypoglycemic range, especially in patients with unstable hemodynamics or receiving insulin infusion, we should be aware that current blood glucose-monitoring technology has not reached a high enough degree of accuracy and reliability to lead to appropriate glucose control in critically ill patients,” wrote Inoue et al.1
A statistical simulation model evaluated the clinical significance of POCT precision. In this study, pairs of “meter-measured” and “laboratory-measured” glucoses were randomly generated based on a mathematical model of total glucose meter error. The study concluded that a glucose meter total precision of less than 1-2% is required to ensure similar insulin dosage compared to the laboratory methods more than 95% of the time. Unfortunately, none of the current POCT devices currently available on the market are capable of providing this level of precision. A review of a recent POCT proficiency testing indicated that current precision ranges from 2-11%, depending on the instrument and analytical methodology.2
Other research has stated, “Having access to immediate test results through POCT is associated with the same or better medication adherence compared with having test results provided by a clinical pathology laboratory (our emphasis). POCT used in general practice can provide general practitioners and patients with timely and complete clinical information, facilitating important self-management behaviors such as medication adherence.”3
To meet the challenge of fast turnaround time to facilitate patient-physician interaction, there are ongoing developments toward a POCT test for hemoglobin A1c that would mirror laboratory measurements for the same marker.
Is POCT a crystal-clear approach for patients to monitor their own glucose? Of course not-the patients will have the same analytical problems as the laboratory. In addition to those, they will also have questions about the meaning of the results, even if a physician has written a “cheat sheet” on what the results might mean with the required treatment adjustment. This seems like a reason to be cautious about proposing POCT to certain patients.
Murata T et al.4 recruited 148 adult type 1 diabetes mellitus patients. ðAccording to their research, the odds of achieving a target HbA1c level of less than 8% was significantly higher in subjects with self-monitoring glucose (SMG) frequencies of greater than or equal to 3.5 times per day compared with those with SMG frequencies of less than 3.5 times per day in the self-injecting insulin group. A SMG frequency of less than 3.5 times per day appeared to be a risk factor for poor glycemic control (HbA1c greater than or equal to 8%) in type 1 diabetes mellitus patients on continuous subcutaneous insulin infusion.4
In addition to measuring glucose with POCT instruments, it is now possible to measure Hgb A1c with POCT. These methods seem more precise than some POCT. The drawback of A1c is that it measures the glucose level from a long period rather than previous few hours. Another potential limiting factor is the cost per A1c test-mainly for patients without health coverage. Having said that, there are reasons to have access to both glucose and A1c available for both patients at home and in a hospital or office.
Tomorrow-the Light at the End of the Tunnel?
The next possible POCT device for glucose monitoring is an instrument that can measure glucose every 5 seconds, using biosensors or continuous glucose monitoring devices (CGM). The data indicates that this monitor is quite useful and is more precise and accurate that glucose meters. Recent studies in the hospital setting have reported that the use of CGM can provide real-time information about glucose concentration, direction and rate of change over a period of several days.
Because it provides glucose values every 5-10 minutes, 24 hours a day, CGM may have an advantage over POCT with respect to reducing the incidence of severe hypoglycemia in acute care. Real-time CGM technology may facilitate glycemic control and reduce hypoglycemia in insulin-treated patients.5 The two major disadvantages are that this CGM is invasive and much more expensive than a glucose meter.5
The main advantage of CGM is that it can provide a near-continuous read-out of interstitial glucose concentration, which adequately reflects blood glucose concentration and can help to identify trends and patterns in glucose control with only a single needle stick to place the sensor. In addition, in the case of real-time CGM, monitors can be programmed to alarm for either high or low glucose values, thus allowing parents and youth to treat for these abnormal values and potentially reducing fear related to hypo- or hyperglycemia.
Disadvantages include the cost of CGM, lack of universal insurance coverage for this technology, limited FDA approval for CGM devices in youth and cosmetic (e.g., additional infusion site/monitor) and psychological concerns (e.g., frustration, helplessness if glucose control is not perceived as adequate). There is also limited evidence supporting use of CGM in youth with type 1 diabetes as a means of improving long-term glycemic control.
One barrier to CGM use appears to be youths’ willingness to accept and use this technology for diabetes management, a problem which likely will need to be addressed before it is possible to adequately examine for the efficacy of CGM use on glycemic control.6 Others have examined the cost of CGM in terms of the expenses of hospitalization for hypo- or hyperglycemia. This approach suggested that, overall, CMG is cost-efficient and can improve quality of life and longevity.7
1. Accuracy of blood glucose measurements using glucose meters and arterial blood gas analyzers in critically ill adult patients: systematic review. Inoue S, et al. Crit Care. 2013 Mar 18;17(2):R48. doi: 10.1186/cc12567. J Diabetes Sci Technol. 2015 Mar;9(2):268-77. See also: Comparative performance assessment of point-of-care testing devices for measuring glucose and ketones at the patient bedside. Ceriotti F, et al. J Diabetes Sci Technol. 2015 Mar;9(2):268-77.
2. Tonyushkina K. M.D. and James H. Nichols, Ph.D., DABCC Glucose meters: a review of technical challenges to obtaining accurate results. Med J Aust. 2009 Nov 2;191(9):487-91.
3. Gialamas A. et al. Does point-of-care testing lead to the same or better adherence to medication? A randomized controlled trial: the POCT in General Practice Trial. Fam Pract. 2010 Feb;27(1):17-24.
4. Murata T. et al. The relationship between the frequency of self-monitoring of blood glucose and glycemic control in patients with type 1 diabetes mellitus on continuous subcutaneous insulin infusion or on multiple daily injections, J Diabetes Investig. 2015 Nov;6(6):687-91.
5. Gomez AM, Umpierrez GE, Continuous glucose monitoring in insulin-treated patients in non-ICU settings, J Diabetes Sci Technol. 2014 Sep;8(5):930-6.
6. Vazeou A. Continuous blood glucose monitoring in diabetes treatment. Diabetes Res Clin Pract. 2011 Aug;93 Suppl 1:S125-30.
7. Patton SR, Clements MA. Continuous Glucose Monitoring Versus Self-monitoring of Blood Glucose in Children with Type 1 Diabetes. Are there Pros and Cons for Both? US Endocrinol. 2012 Summer;8(1):27-29.
David Plaut is a chemist and statistician in Plano, Texas; Natalie Lepage is a clinical biochemist and a biochemical geneticist at the Children’s Hospital of Eastern Ontario and associate professor in the department of pathology and laboratory medicine at the University of Ottawa, Ontario, Canada.