Blood Glucose Readings After High-Dose Intravenous Vitamin C

By Dr. James A. Jackson

It has been discovered that high dose intravenous ascorbic acid (AA), at 15 grams or higher, will cause a “false positive” on various finger stick blood glucose strips read on a “meter.” This is of major importance in a cancer patient receiving this treatment if the patient has diabetes.

For some reason, the strips appear to be “reading” ascorbic acid as glucose. The two molecules are very similar. This false positive does not occur when the test on glucose is performed on serum using the reference hexokinase glucose method, the procedure used in our laboratory.

This is of major importance in a cancer patient receiving this treatment if the patient has diabetes.

To check and see if the IV AA will elevate a patient’s glucose, the Bio-Center Laboratory and Center physicians tested serum glucose levels in six patients receiving various levels of IV AA. The results are shown below:

Grams of AA
15 grams
15 grams
25 grams
50 grams
50 grams
50 grams

Pre IV AA glucose
92 mgs/dL
89 mgs/dL
130 mgs/dL
81 mgs/dL
88 mgs/dL
101 mgs/dL

Post IV AA glucose
85 mgs/dL
85 mgs/dL
103 mgs/dL
85 mgs/dL
92 mgs/dL
86 mgs/dL

In another study, a volunteer (me) received 25 grams of intravenous AA in water (Mega-C-Acid Plus, Ascorbic Acid Injection, 500 mg/mL, MeritPharmaceuticals, Los Angeles, CA 90055. (Note: One drop of this solution on the glucose strip gave an error code E4, “Too high to read!”).

Before the infusion, a pre finger stick glucose, a serum glucose, and a plasma AA were performed. After 30 minutes into the infusion (Mid), and immediately after the infusion (Post), another finger stick glucose, serum glucose, and plasma AA were performed.

The results are shown in the following table:
Finger stick glucose±, serum glucose’, and plasma AA’, pre, mid, and post 25 grams IVAA
Pre IV AA             Mid Pre IV AA          Post IV AA
Finger stick glucose       110 mg/dL               251 mg/dL           363 mg/dL
Serum glucose                110 mg/dL               103 mg/dL             96 mg/dL
Plasma ascorbic acid     3.2 mg/dL             69.2 mg/dL            101 mg/dL

±=Precision Xtra Instrument® XCA170-2151 and MediSense® Precision Xtra blood glucose strips, lot #40872, Abbott Laboratories, Abbott Diabetes Care, Alameda, CA 94502: Glucose control solutionMID®, lot#57802,range 67 to 123 mg/dL. Controls run before and after were 97 mg/dL and 101 mg/dL.

• =Enzymatic method run on the COBAS MlRAPlus® using a reagent kit, Glucose-SL Assay®) from Diagnostic Chemicals Limited, Oxford, CT 06478. The method is a totally enzymatic method using hexokinase and glucose-6-phosphate dehydrogenase.

‘=High Performance Liquid Chromatography method performed on 3.0 mL of plasma mixed with cold 4.5 mL of 3% metaphosphoric acid, mixed by vortex, centrifuged, and the sample run immediately or frozen. See for more information on this test.

After the post blood measurements, finger stick glucose values were performed at 30 minute intervals up to 3 1/2 hours in order to determine how long the AA would affect the blood glucose strips. One hour after the post IV AA (363 mg/dL), the finger stick glucose was 269 mg/dL; after two hours it was 181 mg/dL; 3 1/2 hours later it was 138 mg/dL. The readings were discontinued since the patient had  not eaten lunch or dinner. It would appear that in this case, it took two hours for the glucose measurement on the finger stick to fall to half the pre-IV level (181 mg/dL from 363 mg/dL). Of course, higher blood levels of AA may prolong this time, based on the serum half-life of AA.

The plasmaAA concentrations are interesting. The product insert for the blood glucose strip states that vitamin C levels of up to 2.3 mg/dL will not interfere with the glucose reading. The pre level was 3.2 mg/dL and DID NOT interfere with the strip, (110 mg/dL on both the strip and serum glucose).

However, values of 69.2 mg/dL of plasma AA increased the finger stick glucose to 251 mg/dL, and 101 mg/dL increased the finger stick to 363 mg/dL! None of the serum glucose results were affected.

In two other cases reported to Dr. Jackson (using the same ABBOTT system), both finger stick glucoses read 495 mg/dL. In one elderly patient with metastatic colon cancer and diabetes, a finger stick glucose was performed after a high dose IV AA treatment. Her finger stick glucose read 495 mg/dL! She was given 30 units of insulin and later went into hypoglycemic shock! Her husband was a physician and fortunately she recovered. When contacted by us, the daughter was instructed to obtain a finger stick blood glucose and serum glucose before the next IV injection. Because of anemia, only a finger stick glucose was performed; it read 131 mg/dL. After the IV AA treatment, the finger stick glucose was 495 mg/dL while the serum glucose was 151 mg/dL!

In the second case, a patient with diabetes received a high dose IV AA treatment. While walking away, she fainted. The finger stick glucose was 495 mg/dL. They phoned us and were asked to do a serum glucose from the local laboratory. It was normal.  They also had one of their employees give a serum glucose sample. She then received a 15 gram IV AA infusion. At the end of the IV infusion, another serum glucose was performed. Both the pre and post IV AA serum glucose tests were normal.

We have had five reports of false positive finger stick glucose readings after high-dose IV AA. We know of two other physicians who also found out this interference. Unfortunately, we do not have the name of the other meters or finger stick products, but since the test principle is probably the same in all strips, the interference will also occur.

The authors hope that all healthcare workers will be aware of this potential for false positives on the finger stick glucose method following high dose IV AA and caution the diabetic patient to wait about six to eight hours before performing the test. If a glucose test is needed before that time, a serum glucose may be from a certified laboratory. It does not appear that oral intake of vitamin C in any form will affect the finger stick glucose procedure. We have included this warning of false positive finger stick glucose results on all IV AA protocols and on our websites.