7/28/2019 False Positive Finger Stick Blood Glucose - Vitamin C

1/3

Special ReportFalse Positive Finger Stick Blood GlucoseReadings After High-Dose IntravenousVitamin C

It has been discovered that high-dose intravenous ascorbic acid (AA), at15 grams or higher, will cause a "falsepositive"on various finger stick bloodglucose strips read on a "meter." This isof major importance in a cancer patientreceiving this treatment if the patient alsohas diabetes.For some reason the strips appear tobe "reading" ascorbic acid (or perhaps thedehydro-ascorbic acid) as glucose. Thetwo molecules are very similar. The mo-lecular weight of glucose is 180.16 whilethat of ascorbic acid is 176.12.This false positive does not occurwhen the test is performed on serumglucose using the hexokinase glucose ref-erence method, the procedure used in ourlaboratory. The BioCenter Laboratory andCenter Physicians tested serum glucoselevels in six patients receiving variouslevels of I.V. ascorbic acid. The serumglucose was not affected by the high doseAA. The results are shown below:Amount Pre I.V. AA Post I.V. AAof AA glucose glucose

In another study, one of the authorsUAJ) received 25 grams of intravenousAA in water (Mega-C-Acid Plus, Ascor-bic Acid Injection", 500 mg/mL, MeritPharmaceuticals, Los Angeles, Ca 90055).One drop of this solution placed on theglucose strip read on the Abbott metergave an error code "Too high to read," orover 500 mg/dL.Before the infusion, a pre finger stick

g n zglucose, a serum glucose and a plasmaAA were performed. Thirty minutes intothe i nhsion (Mid), and immediately afterthe infusion (Post), another finger stickglucose, serum glucose and plasma AAwere performed. The results are shownin Table 1 (p.189).

After the post blood measurements,finger stick glucose values were performedat 30 minute intervals up to 3.5 hoursin order to determine how long the AAwould affect the blood glucose strips. Onehour after the post I.V. AA (363 mg/dL),the finger stick glucose was 269 mg/dL;after two hours it was 181 mg/dL; 3.5hours later it was 138 mg/dL. The readingswere discontinued since the patient hadnot eaten lunch or dinner. It would appearthat in this case, it took two hours for theglucose measurement on the finger stickto fall to half the pre-IV level (181 mg/dLfrom 363 mg/dL). Of course, higher bloodlevels of AA may prolong this time, basedon the serum half-life of AA.

The plasma AA concentrations areinteresting. The product insert for theblood glucose strip states that vitamin Clevels of up to 2.3 mg/dL will not interferewith the glucose reading. The pre level was3.2 mg/dL and DID not interfere with thestrip, (110 mg/dL on both the strip andserum glucose).

However, values of 69.2 mg/dL of plas-ma AA increased the finger stick glucoseto 251 mg/dL and 101 mg/dL increasedthe finger stick to 363 mg/dL! None of theserum glucose results were affected.

In two other cases reported to Dr.Jackson (using the same Abbott system),both finger stick glucose readings were495 mg/dL. In one elderly patient withmetastatic colon cancer and diabetes, afinger stick glucose was performed aftera high dose I.V. AA treatment. Her fingerstick glucose read 495 mg/dL! She wasgiven 30 units of insulin and later wentinto hypoglycemic shock! Her husbandwas a physician and fortunately she

7/28/2019 False Positive Finger Stick Blood Glucose - Vitamin C

2/3

Special Report

Table 1. Finger stick glucosea, serum glucoseb and plasma AAc, pre, mid and post25 grams I.V. AA.

Pre I.V. AA Mid I.V. AA Post I.V. AAFinger stick glucose 110 mg/dL 251 mg/dL 363 mg/dLSerum glucose 110 mg/dL 10 3 mg/dL 96 mg/dLPlasma ascorbic acid 3.2 mg/dL 69.2 mg/dL 101 mg/dL

a. Precision Xtra In stru me nts XCA170-2151 and Med iSenses Precision Xtra blood glucose strips, lo t #40872, Abbott Lab orato-ries, A bbo tt Diabetes Care, Alameda, CA 94502: Glucose contro l solution MID@, lot #57802, range 67 to 123 mg/dL. Controls runbefore and after were 97 m gl dt and 101 m gld l.b. Enzymatic method run on the COBAS MlRA Plus@using a reagent kit, Glucose-SL Assay@) rom Diagnostic Chemicals Limited,Oxford, CT 06478. The me thod is a totally enzym atic meth od using hexokinase and glucose-6 -phosphate dehydrog-enase.c. High Performance Liquid Chromatography metho d performed on 3.0 mL of plasma mixed wi th cold 4.5 mL of 3% metaphosphoricacid, m ixed by vortex, centrifuged and the sample run im mediately or frozen. See ww w.biocenterlab.org for more informationon this test.

recovered. When contacted by us, thedaughter was instructed to obtain a fingerstick blood glucose and serum glucosebefore the next I.V. injection. Because ofanemia, only a finger stick glucose wasperformed: it read 131 mg/dL. After theI.V. AA treatment, the finger stick glucosewas 495 mg/dL while the serum glucosewas 151 mg/dL!

In the second case, a patient with dia-betes received a high dose I.V. AA treat-ment. While wallung away, she fainted.The finger stick glucose was 495 mg/dL.They phoned us and we suggested they doa serum glucose from the local laboratory.It was normal. They also had one of theiremployees volunteer to give a pre I.V.serum glucose sample and receive a 15gram I.V. AA infusion. At the end of theI.V. infusion, another serum glucose wasperformed. Both the pre and post I.V. AAserum glucose tests were normal.

We checked 13 more patients (non-diabetic) receiving I.V. AA at 15 to 100

gram doses, some post I.V., some duringthe I.V. In all cases the strips and metersgave very elevated reading, five greaterthan 500 mg/dL. The Abbott meter andstrip also gave a warning reading of "highketones."

One of our physicians asked if thefinger stick glucose correlated with theplasma AA levels. When looking at thefew data points from our experiment, aninteresting correlation was found. Sincethis is only one set of results (n=l) , t mayonly be a coincidence. The finger stickglucose levels in the mid and post samplesappeared to be about 3.5 times higher thanthe plasma AA levels. When the fingerstick glucose levels were divided by 3.6one could get a close approximation of theplasma AA levels at low levels. The midfinger stick glucose level was: 251 mg/dL:251 mg/dL t 3.6 = 69.7 mg/dL AA (theactual value was 69.2 mg/dL).

The post I.V. finger stick glucose was363 mg/dL:

7/28/2019 False Positive Finger Stick Blood Glucose - Vitamin C

3/3

Journal of Orthomolecular Medicine Vol. 21, No. 4, 2006

363 mg/dL s 3.6 = 100.8 mg/dL AA (theactual was 101 mg/dL).

However, this information has littleclinical use since the highest blood glu-cose level that can be obtained with theAbbott finger stick glucose and meteris 500 mg/dL. Therefore, one could onlyconvert to a plasma AA equivalent of138.9 mg/dL (500 t 3.6 = 138.9 mg/dL).One would have to have an abnormalreading (with dilutions) of 1400 mg/dLto get about a 388 mg/dL equivalent. Thelinearity would not allow this conversionto be accurate.

These finding with two of the AbbottCompany's instruments were called intotwo different "customer service person-nel" at Abbott Laboratories cautioningthem of these findings. We offered toshare our findings with them. Later arepresentative said that the "scientific"department had checked this and foundthat it was true and would make a cor-rection to the product insert.

We have had five reports of falsepositive finger stick glucose readingsafter high-dose I.V. AA. We know oftwo other who also found this interfer-ence. Unfortunately, we do not have thename of the other meters or finger stickproducts, but since the test principle isprobably the same in all strips, the in-terference will also occur. We do knowthat the Bayer Glucometer Elite XLTMwith the Ascensia EliteTMtrips and theKrogerTM eter and strips all give a falsepositive glucose reading after high doseI.V. AA. The Abbott product insert statesthat the strip readings from patients andother experiments were compared to theYellow Springs Analyzer" (YSI), not thereference hexokinase chemical method.The YSI analyzer and newer glucose stripsmake use of a small electrical currentgenerated when blood glucose comes incontact with the reagents in the strip.The reagents listed On the Abbott stripare Glucose Dehydrogenase (Microbial)

>0.03U, NAD+ (as sodium salt) >1.0pg,Phenanthroline quinone >0.02 pg, Non-reactive ingredients 216.3 pg. The oldercolormetic glucose strips did not showthis false positive reaction.

The authors hope that all health careworkers will be aware of this potential forfalse positives on the finger stick glucosemethod following high dose I.V. AA andcaution the diabetic patient to wait abouteight hours before performing the test . Ifa glucose test is needed before that time,a serum glucose may be obtained from acertified laboratory using the hexokinasemethod, not the YSI analyzer. It does notappear that oral intake of vitaminC in anyform will affect the finger stick glucoseprocedure. One of the authors is a TypeI1 diabetic and takes a minimum of sixgrams of oral vitamin C a day. It has notcaused a rise in his serum or finger stickglucose.

-James A. Jackson, Ph.D.Contributing Editor, JOM

Director of the BioCenter LaboratoryRonald Hunninghake, M.D.

Chief Medical OfficerChad Krier, N.D., D.C.

Rebecca Kirby, M.D.Glen Hyland, M.D.

The Center for the Improvement ofHuman Functioning International, Inc.,3100 N Hillside Ave, Wichita, KS 67217

www.brightspot.org