Vitamin C and urine test stripsHandling the impact on erythrocytes and glucose results

Urine test stripsA reliable tool in diagnostic

A well proven diagnostic toolThe utilization of urine test strips, within both hospitals and outpatient services alike, is routinely practiced. Urine test strips provide not only a sophisticated means of ensuring rapid diagnostic success, but are also quite cost effective. Some authors consider the microscopic examination of urine samples to be unnecessary if the macroscopic urinary inspection and urine strip testing are normal.1-4 Although such recommendations have to be evaluated in context, taking into account all aspects of the individual patient’s medical history, urine test strips have rightly earned a high degree of trust throughout the modern medical community.

Boehringer Mannheim (today under the name of Roche) launched its fi rst Combur-Test® strip*

Leipzig Academy of Science published a report on rapid urinalysis for different parameters

Viennese chemist Fritz Feigl published his ideas on “spot analysis”

The German chemical company “Helfenberg AG” fi rst commercially offered reagent papers

George Oliver, an English physiologist, markets his “Urinary Test Papers”

Jules Maumené experimented with impregnated merino wool to detect glucose in urine1850

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Diagnostic reliabilty of urine test stripsToday urine test strips are a widely used simple procedure for rapid and reliable detection, as well as, semi-quanti-tative determination of particular parameters. However, the presence of certain agents, or even the improper handling of the urine specimen itself, could interfere with the test’s ability to deliver reliable results. Apart from contamination (e.g. germicides) or the prolonged exposure to light and room-temperature, physicians should

From ancient times until todayIt is quite common for medical staffs to use urine speci-mens to diagnose selective conditions, but from ancient times until the Victorian era, urine analysis was the primary diagnostic tool. It could be said that laboratory medicine started 6000 years ago with the analysis of human urine, termed uroscopy until the 17th century. Today we refer to this practice as urinalysis.5 Considered as the pathfi nder of modern test strip urinalysis is the Viennese chemist Fritz Feigl. Feigl in the 1920s published his results referred to as the “spot reaction” method, a more rapid testing method for certain urine compounds by fi lter paper impregnation with particular reagents.

be cognizant of the potential existence of metabolites occurring from drugs or nutrients in the patient’s urine.

Of particular importance is the presence of high amounts of Vitamin C, which can cause false-negative results for the parameters erythrocytes (hemoglobin) and glucose, two very important indicators for a couple of severe diseases.

From the many parameters that could interfere with the reliability of urine test strips, Vitamin C is of vital importance.

HandlingProlonged exposure to light and room-temperature alter the concentration of certain metabolites

NutritionEnhanced concentrations of nutrition metabolites (e.g. Vitamin C) may alter test pad functionality

Contaminatione.g. with hospital germicides may alter pH level of the specimen

Patient’s medicationMetabolites from drugs in the patient’s urine may interfere with the detectability of some parameters

Impacts on diagnostic reliability

Diagnostic reliability of urine test strips can be influenced by improper handling, contamination of the urine sample, metabolites from drugs or nutrition.

Vitamin C is widely distributed in fruits and vegetables, as well as, artificially added in commercially available food and beverages.

Vitamin CHealthy, powerful and interfering

Nutrition and Vitamin CVitamin C, probably the most famous amongst the vita-mins, is also referred to as ascorbic acid or ascorbate. It belongs to the water-soluble class of vitamins. Vitamin C is widely distributed in fruits and vegetables thus making it relatively easy to acquire the recommended daily dosage essential for meeting the requirements of a balanced diet. In addition, the enhanced use of Vitamin C as an additive in many foods and beverages, as well as, the presence of Vitamin C in several health supple-ments creates the potential for the general population

The impact on urinalysisAs a result of increased consumption, high Vitamin C concentrations of >400 mg/L are increasingly found in urine samples.23 The presence of such high concentra-tions has been known to cause signifi cant problems with urine strip testing.

Vitamin C reduces the oxidized indicator substances which can lead to false-negative results when analyzing glucose and erythrocytes (hemoglobin).19 Such serious progressive illnesses as diabetes mellitus, glomerulonephritis, and bladder tumors could go underdiagnosed.

Catabolism of Vitamin CVitamin C can be absorbed by active transport in the intestine.9 Up to 100 mg/day the absorption level is at 80-90% . Higher levels reduce the effi ciency of absorp-tion.10 The average body tissue of an adult stores only 1.2-2.0 g presumably maintained by taking 60-75 mg per day.11-15 The total body pool of ascorbic acid is saturated by taking approximately 140 mg per day.16 The average half life of Vitamin C amounts to 10-20 days17, being inversely

Higher doses of Vitamin C result in unchanged excretion

Total body pool of Vitamin C is saturated at 140 mg per day

Average adult stores only 1.2-2.0 g in body tissue

Urinary excretion

Total body pool

Min. requirement

60-75 mg per day

140 mg per day

> 60 mg per day

Urinary excretion of Vitamin C

proportional to the dosage.15 Urinary excretion starts with plasma ascorbate concentrations of about 1.2-1.8 mg/dL.18 They are considered to be the renal threshold. Threshold urinary excretion of ascorbic acid was reported at already 60 mg doses per day.11,12,15 Ingestion of higher doses of Vitamin C results in increased and unchanged excretion without re-absorption by the kidneys.11-15

Prevention of false-negative results The understanding of these false-negative results has contributed to the development of suitable approaches to minimize the interference of ascorbic acid, thus prevent-ing false-negative results from occurring in the future when using urine test strips. One obvious approach has been to test urine specimens at least 10 hours after the last intake of Vitamin C.20 Another approach may be as simple as the use of urine test strips that include an additional pad for the detection of Vitamin C thus verify-ing a urine sample is free of this substance. However, if Vitamin C is detected, time-consuming patient revisits and retests might be inevitable. These revisits are both costly for the patient and physician, and might lead to delayed treatment.

Certainly, a more diff erentiated approach would be to use urinalysis test strips that are resistant to ascorbic acid, like the Combur-Test® strip*.

1 x 2 x10 hOption 1

Use Vitamin C resistant tests like Roche's Combur-Test®

strip*

Option 2Use strip with additional pad that indicates the presence of Vitamin C. Use option 3, if positive and repeat test

Option 3 Avoid Vitamin C as much aspossible: Instruct your patientto avoid additional Vitamin Cconsumption for at least 10 h prior to revisiting your practice

Prevent against false-negative results and potential under diagnoses

to be exposed to excessively large amounts of ascorbic acid on a daily basis.6 The food industry routinely uses Vitamin C as a natural antioxidant, to preserve color, to enhance aroma, and as a nutritional additive. The meat processors use Vitamin C to facilitate the reduction of both the amount of added nitrite, as well as, residual nitrite content in their products.7 The addition of Vitamin C to fresh fl our is commonly used to reduce the 4-8 weeks of maturation time fl our would normally have to undergo after milling, thus improving its baking qualities.8

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1 Vitamin C availability in generalThe accessibility of Vitamin C within the commercially available food supply more than covers the individual daily requirement

2 Vitamin C as a product featureDue to its widely accepted associated health benefi ts, the food and beverage industry routinely adds ascorbic acid to its list of ingredients as a promotional benefi t

3 Vitamin C as health supplement The increased level of public interest for personal health care has led to an increase in self-prescribed overmedication with readily available over-the-counter drugs (e.g. Vitamin C, as well as, many other popular vitamins in western countries)

4 Vitamin C as a preservativeAscorbic acid is routinely used in the food industry as an inex-pensive preservative, a discoloration inhibitor and an antioxidant

Sources of Vitamin C in modern nutrition

Combur-Test® strips*Resistant to Vitamin C

Vitamin C is common and widely usedA higher intake of ascorbic acid in the general population is triggered by lifestyle and health awareness, and by the food and beverage industry where it is used as a preservative, an antioxidant and a health supplement

Iodate impregnation of the test area is an optimal solutionAn iodate impregnated component significantly reduces the effect of ascorbic acid interference. Tests have discovered that some urine test strips available on the market are report-ing a potentially dangerous false-negative result for glucose and erythrocytes (hemoglobin) even in the presence of small amounts of Vitamin C. These false-negative results could have serious consequences for doctor and patient alike

Vitamin C interferes with the reliabilty of urine test stripsHigh ascorbic acid concentrations of >400 mg/L are increasingly being found in the urine samples tested by laboratories.23 The presence of such high concentrations is known to cause significant problems with urine strip testing because ascorbic acid can, and often will, lead to false-negative results. In particular, there are specific inconsistencies when analyzing glucose and erythrocytes (hemoglobin)

Combur-Test® strip* provides best results even at high concentrations of ascorbic acidCombur-Test® strip* detects even low concentrations of glucose and erythrocytes (hemoglobin) in the presence of Vitamin C giving you accurate results you can rely on

In summaryProblems exist with test strip urinalysis in the presence of Vitamin C that may influence the test’s ability to provide clinically secure results.

Combur-Test® strip* is equiped with an iodate impregnation that allows a reliable semi-quantification for erythrocytes (hemoglobin) and glucose even in the presence of high concentrations of Vitamin C in the patient’s specimen.

The Combur-Test® strip* promisePatients revisits and – even more important – patients retests could be avoided just by eliminating interference from Vitamin C. Even at high levels up to 750 mg/L Vitamin C in the specimen, Combur-Test® strips* provide reliable results for the disease-critical parameters of glucose and erythrocytes (hemoglobin).

Iodate impregnation makes the differenceIn order to diminish the interference, ascorbic acid can be oxidized to dehydroascorbate acid, by incorporating an oxidant into the test strips. It was shown that mer-curic acetate is able to eliminate the negative impact of ascorbic acid.21 Also impregnation with iodate removes interference of ascorbic acid effectively.22 The latter is used in Combur-Test® strips*. An iodate-impregnated reagent paper is added in the erythrocytes (hemoglobin) and glucose test pads in order to guarantee reliable results.

Most resistant compared to competitorsRecent tests have discovered that some urine test strips available on the market are reporting a potentially dan-gerous false-negative result for glucose and erythrocytes (hemoglobin) even in the presence of small amounts of Vitamin C.

In a study performed by Nagel et al., five very common 10-parameter urine test strips from different manufacturers were compared. Combur-Test® strips* showed the best error tolerance against Vitamin C even in the lowest, but clinically relevant concentrations of glucose and erythrocytes (hemoglobin).23

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Summary

Combur-Test® strips* showed the best error tolerance against Vitamin C in the specimen, even at lowest concentrations of glucose and erythrocytes.34

The presence of high amounts of Vitamin C in the patient's urine is very common. Combur-Test® strips* could help to prevent patient revisits caused by unreliable test results.

COBAS, LIFE NEEDS ANSWERS, CHEMSTRIP, COMBUR-TEST and COMBUR 10 TEST are trademarks of Roche.

©2010 Roche

Roche Diagnostics Ltd.CH-6343 RotkreuzSwitzerlandwww.roche.com

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References1 Shaw ST, Jr., Poon SY, Wong ET (1985). ‘Routine urinalysis’. Is the

dipstick enough? JAMA. 253, 1596-1600.2 Wenz B, Lampasso JA (1989). Eliminating unnecessary urine

microscopy. Results and performance characteristics of an algo-rithm based on chemical reagent strip testing. Am J Clin Pathol. 92, 78-81.

3 High S, Rowe J, Maksem J (1988). Macroscopic physicochemical testing for screening urinalysis. Lab. Med. 19, 174-176.

4 Cramer A, Chogyoje M, Saxena S, Appleman M, Wong E (1989). Macroscopic screening urinalysis. Lab Med. 20, 623-627.

5 Armstrong JA. Kidney International (2007) doi:10.1038/sj.ki.5002057, published online 27 December 2006. 71, 384–387.

6 Newsome, RL (1987). Use of vitamins as additives in processed foods. Food Technol. 41(9), 163.

7 Izumi, K (1992). Reaction of nitrite with ascorbic acid or ascorbic acid-2-derivatives. J. Food. Sci. 57, 1066.

8 Elkassabany, M, Hoseney, RC and Seib, PA (1980). Ascorbic acid as an oxidant in wheat flour dough. Cereal Chem. 57, 85.

9 Sauberlich HE (1985). Bioavailability of vitamins. Prog Food Nutr Sci. 9, 1-33.

10 Naidu KA (2003). Vitamin C in human health and disease is still a mystery? An overview. Nutr J. 2, 7.

11 Baker EM, Hodges RE, Hood J, Sauberlich HE, March SC (1969). Metabolism of ascorbic-1-14C acid in experimental human scurvy. Am J Clin Nutr. 22, 549-558.

12 Baker EM, Hodges RE, Hood J, Sauberlich HE, March SC, Canham JE (1971). Metabolism of 14C- and 3H-labeled L-ascorbic acid in human scurvy. Am J Clin Nutr. 24, 444-454.

13 Hodges RE, Baker EM, Hood J, Sauberlich HE, March SC (1969). Experimental scurvy in man. Am J Clin Nutr. 22, 535-548.

14 Hodges RE, Hood J, Canham JE, Sauberlich HE, Baker EM (1971). Clinical manifestations of ascorbic acid deficiency in man. Am J Clin Nutr. 24, 432-443.

15 Kallner A, Hartmann D, Hornig D (1979). Steady-state turnover and body pool of ascorbic acid in man. Am J Clin Nutr. 32, 530-539.

16 Sauberlich H (1990). Ascorbic acid. In: Brown M, ed. Present knowledge in nutrition. Nutrition Foundation, Washington DC, 1990.

17 Hellman L, Burns JJ (1958). Metabolism of L-ascorbic acid-1-C14 in man. J Biol Chem. 230, 923-930.

18 Pietrzik K, Loew D, Golly I (2008). Vitamin C. In:Handbuch Vita-mine. Für Prophylaxe, Therapie und Beratung. Urban & Fischer, Elsevier GmbH, 2008. 173-185.

19 Nagel D, Seiler D, Hohenberger EF, Ziegler M (2006). Investiga-tions of Ascorbic Acid Interference in Urine Test Strips. Clin. Lab. 52, 149-153.

20 Ringsrud KM (1995). Urinalysis and Body Fluids a ColorText and Atlas. St. Louis et al. Mosby, 73.

21 White-Stevens RH (1982). Interference by ascorbic acid in test systems involving peroxidase. I. Reversible indicators and the effects of copper, iron, and mercury. Clin Chem. 28, 578-588.

22 Brigden ML, Edgell D, McPherson M, Leadbeater A, Hoag G (1992). High incidence of significant urinary ascorbic acid con-centrations in a west coast population – implications for routine urinalysis. Clin Chem. 38, 426-431.

23 Nagel D, Seiler D, Hohenberger EF, Ziegler M (2006). Investiga-tions of Ascorbic Acid Interference in Urine Test Strips. Clin. Lab. 52, 149-153.

* Combur-Test® is marketed under Chemstrip® Test in the USA and Canada** Combur10 Test® UX has been used for the comparison

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