AC Impedance and Multi-Pulse Technology

AC Impedance and Multi-Pulse Technology

A glucose meter measures glucose with direct current (DC): the enzyme on the strip reacts with glucose, producing a current proportional to the glucose in the drop [1]. AC impedance and multi-pulse waveforms are extra electrical questions asked of the same drop. An alternating-current (AC) signal tells the meter whether the strip has filled and carries information about hematocrit and temperature [1]. A multi-pulse waveform changes the voltage during the test, giving the algorithm more data to correct with [2]. Neither measures glucose by itself.

What an AC impedance measurement is

Impedance is a material's opposition to alternating current. Meters use AC because it avoids electrolytic effects at the electrodes [2]. Red blood cells resist current more than plasma does, so more cells mean higher resistance between two fixed electrodes. A relationship worked out by Maxwell, and later applied to blood by Fricke, turns that resistance into an estimate of hematocrit, the share of blood volume made of red cells [2]. Which way hematocrit pushes a reading is covered in Hematocrit (HCT) Interference and Correction.

What the AC step can catch

The most detailed public description we found is FDA's 2011 summary for Roche's Accu-Chek Aviva Plus strips, which gives the AC signal three jobs [1].

• Fill. When the strip goes in, the meter applies a small AC signal and waits. Blood reaching the electrodes causes "a spike in the conductivity" at the measurement electrodes and at separate sample-sufficiency electrodes, and both are used to confirm the drop is big enough [1].
• Hematocrit and temperature. Next the meter applies AC at four frequencies. The responses "carry information about the sample type and environmental temperature" [1].
• Strip and system checks. The same responses "allow the system to perform various internal quality checks" [1]. The summary doesn't say which ones.

Only then does the meter apply a small DC voltage and read the glucose current. It combines the AC and DC information into "a hematocrit and temperature compensated glucose result" [1].

Which meters' FDA summaries name it

Of the FDA summaries we read, only Roche's describe an AC step. The 2005 clearance of the Accu-Chek Aviva system says it "utilizes both AC/DC electrical impedance information," and lists its comparison device, the Accu-Chek Advantage, as using biamperometry [3]. The 2016 summary for the Accu-Chek Guide says "the sample and the environmental conditions are evaluated using AC and DC signals" [4]. As of October 2026, Roche says the Accu-Chek Aviva meter "will soon be discontinued" [5].

An AC step on paper doesn't guarantee a small hematocrit error. In a 2011 lab study across hematocrits of 25% to 60%, the Accu-Chek Aviva's results shifted by 23%, against the study's 10% limit for stable performance [6]. The study was funded by sanofi-aventis, whose own meter was among those tested [6].

The OneTouch Verio Flex [7] and Ascensia Contour Next GEN [8] summaries describe a current proportional to glucose without naming the signal behind it. The Contour Next GEN does catch a short fill, letting the user add blood within 60 seconds [8], but its summary doesn't say how.

What a multi-pulse or dynamic waveform is

A multi-pulse waveform replaces one steady voltage with a planned series of steps, and the meter records how the current responds to each. LifeScan's researchers described the OneTouch Verio system this way in 2012, writing that the meter "uses a novel multipulse signal" with a compensation algorithm covering glucose, hematocrit, temperature and antioxidants [2]. Their figure lays out the 5-second test [2]:

• 20 millivolts for the first second.
• 300 millivolts for 0.3 seconds.
• A brief sine wave from 1.30 to 1.32 seconds, used "to determine that the strip has sufficient sample."
• 300 millivolts again until the 4-second mark.
• −300 millivolts for the final second.

Here's what surprised us: step 3 is a short burst of AC inside a multi-pulse sequence, doing the fill check [2]. The two labels describe overlapping tools, not rival camps. The meter combines the currents from the two long phases to cancel most of the hematocrit effect [2], math we walk through in Hematocrit Interference Correction Algorithms.

LifeScan funded the work, and its authors were LifeScan employees [2]. The paper doesn't say whether later Verio meters run the same waveform; FDA's Verio Flex summary describes only an amperometric measurement [7]. As of October 2026, FDA's device identifier database lists the original OneTouch Verio meter as out of commercial distribution since December 2025, while Verio Flex and Verio Reflect meters and OneTouch Verio strips are still listed as in distribution [9].

Dynamic electrochemistry goes further and adapts the signal as the test runs. The 2011 study describes varying frequencies and voltages and readjusting the input as the reaction progresses, so the output forms a "fingerprint" the algorithm turns into correction factors [6]. FDA's 2011 summary for AgaMatrix's iBGStar, a meter cleared to work with an iPhone app and BGStar test strips, says it uses "dynamic electrochemistry to correct for common analytical interferences such as hematocrit" [10]. In the 2011 study, the BGStar meter's results shifted by 8% across hematocrit levels, inside the 10% limit [6].

What the patent records claim

A patent shows what a company claimed as its invention, not which meter, if any, contains it.

• US 7,407,811 B2, "System and method for analyte measurement using AC excitation," Roche Diagnostics Operations Inc, granted August 5, 2008. Claim 1 covers applying a signal with an AC component, then a DC signal, and combining both responses to report a concentration; a dependent claim limits the AC signal to two to five frequencies [11].
• US 7,452,457 B2, "System and method for analyte measurement using dose sufficiency electrodes," Roche Diagnostics Operations Inc, granted November 18, 2008. It claims judging how far blood has filled the strip from at least two electrode pairs placed along the chamber, with an AC test signal in a dependent claim [12].
• US 8,148,164 B2, "System and method for determining the concentration of an analyte in a sample fluid," Roche Diagnostics Operations Inc, granted April 3, 2012. Its first claim adds a waveform that excites the sample at several frequencies at once [13].
• US 8,425,757 B2, "Gated amperometry," Bayer Healthcare LLC, granted April 23, 2013. It claims at least three duty cycles within 180 seconds, each an excitation followed by a relaxation, and its abstract says these pulse sequences may reduce errors from hematocrit, under-fill and temperature changes [14].

The Bayer patent also makes a practical point about strip faults. Conventional two-electrode systems can flag a "bad" analysis without knowing whether under-fill or a defective strip caused it. Knowing matters, because an under-filled strip can take more blood instead of being thrown away [14].

What the labeling tells you

None of the FDA summaries we read publishes the correction math. They do publish the ranges each system was shown to handle: for the Accu-Chek Guide, 10% to 65% hematocrit and 43 to 113 °F [4]. If your hematocrit runs outside the range your meter is labeled for, which meter suits you is a decision for your care team.