$1.00. manufacturers often provide meters at no cost to induce use of the profitable test strips. type 1 diabetics may test as often as 4 to 10 times a day due to the dynamics of insulin adjustment, whereas type 2 typically test less frequently, especially when insulin is not part of treatment. a recent study on the comparative cost-effectiveness of all options for the self-monitoring of blood glucose funded by the national health service in the uk uncovered considerable variation in the price paid, which could not be explained by the availability of advanced meter features. it estimated that a total of £12 m was invested in providing 42 million self-monitoring of blood glucose tests with systems that fail to meet acceptable accuracy standards, and efficiency savings of £23.2 m per annum are achievable if the national health service were to disinvest from technologies providing lesser functionality than available alternatives, but at a much higher price. batches of counterfeit test strips for some meters have been identified, which have been shown to produce inaccurate results. noninvasive meters main article: noninvasive glucose monitor the search for a successful technique began about 1975 and has continued to the present without a clinically or commercially viable product. as of 1999, only one such product had ever been approved for sale by the fda, based on a technique for electrically pulling glucose through intact skin, and it was withdrawn after a short time owing to poor performance and occasional damage to the skin of users. continuous glucose monitors continuous glucose monitor. the sensor and transmitter are fixed to the upper arm. the reader shows days to replacement of sensor, current blood glucose level and a diagram of the latest blood glucose levels. main article: continuous glucose monitorcontinuous glucose monitor systems can consist of a disposable sensor placed under the skin, a transmitter connected to the sensor and a reader that receives and displays the measurements. the sensor can be used for several days before it needs to be replaced. the devices provide real-time measurements, and reduce the need for fingerprick testing of glucose levels. a drawback is that the meters are not as accurate because they read the glucose levels in the interstitial fluid which lags behind the levels in the blood. continuous blood glucose monitoring systems are also relatively expensive. accuracy accuracy of glucose meters is a common topic of clinical concern. blood glucose meters must meet accuracy standards set by the international organization for standardization (iso). according to iso 15197 blood glucose meters must provide results that are within ±15% of a laboratory standard for concentrations above 100 mg/dl or within ±15 mg/dl for concentrations below 100 mg/dl at least 95% of the time. however, a variety of factors can affect the accuracy of a test. factors affecting accuracy of various meters include calibration of meter, ambient temperature, pressure use to wipe off strip (if applicable), size and quality of blood sample, high levels of certain substances (such as ascorbic acid) in blood, hematocrit, dirt on meter, humidity, and aging of test strips. models vary in their susceptibility to these factors and in their ability to prevent or warn of inaccurate results with error messages. the clarke error grid has been a common way of analyzing and displaying accuracy of readings related to management consequences. more recently an improved version of the clarke error grid has come into use: it is known as the consensus error grid. older blood glucose meters often need to be "coded" with the lot of test strips used, otherwise, the accuracy of the blood glucose meter may be compromised due to lack of calibration. future one noninvasive glucose meter has been approved by the u.s. fda: the glucowatch g2 biographer made by cygnus inc. the device was designed to be worn on the wrist and used electric fields to draw out body fluid for testing. the device did not replace conventional blood glucose monitoring. one limitation was that the glucowatch was not able to cope with perspiration at the measurement site. sweat must be allowed to dry before measurement can resume. due to this limitation and others, the product is no longer on the market. the market introduction of noninvasive blood glucose measurement by spectroscopic measurement methods, in the field of near-infrared (nir), by extracorporal measuring devices, has not been successful because the devices measure tissue sugar in body tissues and not the blood sugar in blood fluid. to determine blood glucose, the measuring beam of infrared light, for example, has to penetrate the tissue for measurement of blood glucose. there are currently three cgms (continuous glucose monitoring system) available. the first is medtronic's minimed paradigm rts with a sub-cutaneous probe attached to a small transmitter (roughly the size of a quarter) that sends interstitial glucose levels to a small pager sized receiver every five minutes. the dexcom system is another system, available in two different generations in the us, the g4 and the g5. (1q 2016). it is a hypodermic probe with a small transmitter. the receiver is about the size of a cell phone and can operate up to twenty feet from the transmitter. the dexcom g4 transmits via radio frequency and requires a dedicated receiver. the g5 version utilizes bluetooth low energy for data transmission, and can transmit data directly to a compatible cellular telephone. currently, apple's iphone and android devices can be used as a receiver. aside from a two-hour calibration period, monitoring is logged at five-minute intervals for up to 1 week. the user can set the high and low glucose alarms. the third cgms available is the freestyle navigator from abbott laboratories. there is currently an effort to develop an integrated treatment system with a glucose meter, insulin pump, and wristop controller, as well as an effort to integrate the glucose meter and a cell phone. testing strips are proprietary and available only through the manufacturer (no insurance availability). these "glugophones" are currently offered in three forms: as a dongle for the iphone, an add-on pack for lg model ux5000, vx5200, and lx350 cell phones, as well as an add-on pack for the motorola razr cell phone. in us, this limits providers to at&t and verizon. similar systems have been tested for a longer time in finland. recent advances in cellular data communications technology have enabled the development of glucose meters that directly integrate cellular data transmission capability, enabling the user to both transmit glucose data to the medical caregiver and receive direct guidance from the caregiver on the screen of the glucose meter. the first such device, from telcare, inc., was exhibited at the 2010 ctia international wireless expo, where it won an e-tech award. this device then underwent clinical testing in the us and internationally. in early 2014 google reported testing prototypes of contact lenses that monitor glucose levels and alert users when glucose levels cross certain thresholds. apple has patented methods for determining blood sugar levels by absorption spectroscopy, as well as by analyzing exhaled air in its electronic devices. technology two used accu-chek test strips. the lower one has had the cover peeled off to show the circuit. many glucose meters employ the oxidation of glucose to gluconolactone catalyzed by glucose oxidase (sometimes known as gox). others use a similar reaction catalysed instead by another enzyme, glucose dehydrogenase (gdh). this has the advantage of sensitivity over glucose oxidase but is more susceptible to interfering reactions with other substances. the first-generation devices relied on the same colorimetric reaction that is still used nowadays in glucose test strips for urine. besides glucose oxidase, the test kit contains a benzidine derivative, which is oxidized to a blue polymer by the hydrogen peroxide formed in the oxidation reaction. the disadvantage of this method was that the test strip had to be developed after a precise interval (the blood had to be washed away), and the meter needed to be calibrated frequently. most glucometers today use an electrochemical method. test strips contain a capillary that sucks up a reproducible amount of blood. the glucose in the blood reacts with an enzyme electrode containing glucose oxidase (or dehydrogenase). the enzyme is reoxidized with an excess of a mediator reagent, such as a ferricyanide ion, a ferrocene derivative or osmium bipyridyl complex. the mediator in turn is reoxidized by reaction at the electrode, which generates an electric current. in order for the mediator to operate over long timeframes, it needs to be stable in both oxidised and reduced states. this is to allow for continuous regeneration of the oxidised form of the mediator for shuttling of electrons from enzyme to active site. osmium-based polypyridyl redox complexes and polymers are attractive candidates as mediators due to their stability in oxidised and reduced forms, tunable redox potential, ease of co-immobilisation and ability to operate at low potentials. the total charge passing through the electrode is proportional to the amount of glucose in the blood that has reacted with the enzyme. the coulometric method is a technique where the total amount of charge generated by the glucose oxidation reaction is measured over a period of time. the amperometric method is used by some meters and measures the electric current generated at a specific point in time by the glucose reaction. this is analogous to throwing a ball and using the speed at which it is travelling at a point in time to estimate how hard it was thrown. the coulometric method can allow for variable test times, whereas the test time on a meter using the amperometric method is always fixed. both methods give an estimation of the concentration of glucose in the initial blood sample. the same principle is used in test strips that have been commercialized for the detection of diabetic ketoacidosis (dka). these test strips use a beta-hydroxybutyrate-dehydrogenase enzyme instead of a glucose oxidizing enzyme and have been used to detect and help treat some of the complications that can result from prolonged hyperglycemia. blood alcohol sensors using the same approach, but with alcohol dehydrogenase enzymes, have been tried and patented but have not yet been successfully commercially developed. meter use for hypoglycemia although the apparent value of immediate measurement of blood glucose might seem to be higher for hypoglycemia than hyperglycemia, meters have been less useful. the primary problems are precision and ratio of false positive and negative results. an imprecision of ±15% is less of a problem for high glucose levels than low. there is little difference in the management of a glucose of 200 mg/dl compared with 260 (i.e., a "true" glucose of 230±15%), but a ±15% error margin at a low glucose concentration brings greater ambiguity with regards to glucose management. the imprecision is compounded by the relative likelihoods of false positives and negatives in populations with diabetes and those without. people with type 1 diabetes usually have a wider range of glucose levels, and glucose peaks above normal, often ranging from 40 to 500 mg/dl (2.2 to 28 mmol/l), and when a meter reading of 50 or 70 (2.8 or 3.9 mmol/l) is accompanied by their usual hypoglycemic symptoms, there is little uncertainty about the reading representing a "true positive" and little harm done if it is a "false positive." however, the incidence of hypoglycemia unawareness, hypoglycemia-associated autonomic failure (haaf) and faulty counterregulatory response to hypoglycemia make the need for greater reliability at low levels particularly urgent in patients with type 1 diabetes mellitus, while this is seldom an issue in the more common form of the disease, type 2 diabetes mellitus. in contrast, people who do not have diabetes may periodically have hypoglycemic symptoms but may also have a much higher rate of false positives to true, and a meter is not accurate enough to base a diagnosis of hypoglycemia upon. a meter can occasionally be useful in the monitoring of severe types of hypoglycemia (e.g., congenital hyperinsulinism) to ensure that the average glucose when fasting remains above 70 mg/dl (3.9 mmol/l).