Interference Study - Macherey-Nagel URYXXON Relax User Manual

15.3.7 Interference study

The influence of possible interfering substances is described for each test parameter:
Blood: Normal concentrations of ascorbic acid (≤ 40 mg/dL) do not influence the test result. In
the case of Combi 11, ascorbic acid concentrations > 2.5 mg/dL lead to false-negative results.
False positive reactions can be caused by residues of peroxide-containing or other cleaning
agents, as well as menstrual blood.
Urobilinogen: The detection is inhibited by higher concentrations of formaldehyde
(> 60 mg/dL). Nitrite concentrations > 2.5 mg/dL and prolonged exposure of the urine to light
can lead to low or false-negative values. Overly high or false-positive results can be caused by
dyes (e.g. betanin) or medications excreted in the urine.
Bilirubin: The detection is inhibited by higher concentrations of ascorbic acid (> 10 mg/dL) and
nitrite (> 2.5 mg/dL). Prolonged exposure of the urine to light can lead to low or false-negative
values. Urine indican at a concentration of > 40 mg/dL may cause false-positive results.
Protein: False-positive findings can occur in the case of extremely alkaline urine (pH > 9),
disinfectant residues (e.g. benzalkonium chloride > 12.5 mg/dL) in the urine container or in the
presence of quinine (> 50 mg/dL).
Nitrite: False-negative results can occur in the case of antibiotic therapy, and in the case of an
overly low nitrate level in the urine as a result of low-nitrate food or severe dilution (diuresis).
Microbes without the ability to form nitrite can also be present. A false-positive reaction color
can be caused by dyes (e.g. betanin) excreted in the urine.
Ketone: Phthalein compounds up to a concentration of 125 mg/dL (highest tested
concentration) do not interfere with the result.
Ascorbic acid: Lower results can occur due to oxidising cleaning agents in sample containers.
Glucose: Normal concentrations of ascorbic acid (≤ 40 mg/dL) do not influence the test result.
False-positive reactions can be caused by oxidising cleaning agents in the sample container.
pH: The dye betanin has no influence on the evaluation of the pH test field up to the highest
tested concentration of 500 mg/dL.
Density: In the case of elevated protein excretion (> 500 mg/dL), the density values determined
are too low.
Leukocytes: An attenuated reaction can be expected if preparations with nitrofurantoin
(> 2 mg/dL) or phenazopyridine (> 0.2 mg/dL) are taken. Formaldehyde (as a preservative,
> 20 mg/dL) and dyes (e.g. betanin) can lead to a false-positive reaction. In the case of
specimens from female patients, a false-positive reaction can be simulated by vaginal secretion.
15.4 Literature
M. J. C. Schot, S. van Delft, A. M. J. Kooijman-Buiting, N. J. de Wit, R. M. Hopstaken, BMJ
Open, 2015, 5, e006857.
K. Ekblom, A. Petersson, Scand. J. Clin. Lab. Invest., 2020, 1, 39–45.
K. Durkalec-Michalski, P. M. Nowaczyk, K. Siedzik, J., J. Int. Soc. Sport Nutr., 2019, 16,16.
Manual URYXXON Relax EN, V 6.03 / 08.22
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