Nitrite Adulteration of Workplace Urine Drug-Testing Specimens I ...

Jourr, al of Analytical Toxicology, Vol. 22, March/April 1998
Metronidazole was of interest because it can be given in doses as
high as 4 g/day. Of the two patients on metronidazole, one was
receiving 1.5 g/day, which produced 0.8 IJg/mL nitrite. Ranitidine
resulted in a similar level of nitrite in the urine. The urinary tract
analgesic phenazopyridine was included. Although not con-
taining a nitro group, it was tested because the Chemstrip
package insert indicated that it might give a false-positive
reading for nitrite because of the orange-red color it imparts to
the urine (15). The modestly increased apparent nitrite con-
centration with phenazopyridine listed in Table II may be due to
color from phenazopyridine. Specimens from patients taking
antifungal and antineoplastic drugs were not tested. The anti-
fungal drugs are applied topically, and relatively little would
reach the urine. With antineoplastic agents, the daily dosage
does not exceed 300 mg of parent drug, and it would not increase
urinary nitrite beyond a few nanograms per milliliter.
Medical care: Medications which stimulate the in vivo for-
mation of nitrite~nitrate through induction of NOS.
]ndomethacin transfusion for premature infants lead to a 25-
fold increase in urine nitrite concentration through a currently
unknown mechanism (26). The increase returned to baseline
after 3 days, indicating that this was a transitory effect not
related to chronic administration. In order to assess the possible
effect of indomethacin in a workplace setting, two male subjecL~
of working age were given a standard dose of indomethacin
(25 rng three times per day) with specimens taken at 2, 8, 12, 24,
and 48 h after the initial dose. All specimens from both subjects
had a nitrite concentration below the limit of detection of the
method, 0.6 lJg/mL. No effect was observed.
lnterleukin-2 in cancer treatment can increase urinary
Table III. Nitrite Concentrations in Urine Specimens Received for
Employment Drug Testing which Appeared to Have Been Adulterated
With Excess Nitrite
Specimen No. Nitrite (pg/mL) Specimen No. Nitrite (pg/mL)
A* 3640 + 17 5490
1 1910 18 6300
2 4400 19 4200
3 7390 20 7030
4 10,700 21 4140
5 6770 22 4530
6 4400 23 2500
7 11,500 24 11,600
8 5420 25 7780
9 12,200 26 6730
10 8340 27 7750
11 6930 28 4040
12 4630 29 4990
13 3810 30 4140
14 3740 31 6540
15 4070 32 2920
16 4560
Average 59 I0
Range 1910-12,200
* Certified drug-negative urir+e i)(x)l, negative by lest strip for nitrite, fotlified with one vial of Klear in 50 mL urine.
r Results rounded to three significant figures because of 1000+f(~kl dilution of specimet~s.
nitrate and nitrite through the induction of cytokines and
NOS (27). This study produced a peak urine nitrate concen-
tration of 183 tJg/mL.
Intentional addition to the urine after voiding
"Fable III lists the concentrations of nitrite found in ~outine
workplace drug-testing specimens which presented to the labo-
ratory with a pattern consistent with adulteration: an initial
test positive (for cannabinoids), a failure to confirm by GC-MS
due to little or no recovery of the ions of 9-THCA and its deuter-
ated internal standard, and a strongly positive reaction for nitrite
on the Chemstrip. A clinical specimen being screened for a uri-
nary tract infection produces a light pink color on the Chem-
strip. A specimen to which Klear has been added (or crystalline
potassium nitrite for experimental purposes) produces a vivid
red-violet color that persists for approximately 20 s and then
fades to a pale orange. Each microtube of Klear contains about
500 mg of potassium nitrite. With a minimal acceptable urine
volume of 30 mL, an estimated maximum volume of 120 mL (as
may occur in a split specimen collection using a collection con-
tainer), a variable percent purity of potassium nitrite (85-96%+),
and the potential for addition of either one or two microtubes of
Klear, a urine specimen to which Klear was added would be
expected to contain between 1900 and 15,000 IJg/mL nitrite.
The 32 specimens suspected of nitrite adulteration ranged from
a low of 1910 to a high of 12,200 1Jg/mL with an average of
5910. None of the 32 specimens had a concentration less than
1500 IJg/mL. Specimen A was prepared in the laboratory by
adding one microtube of Klear to 50 mL of certified drug-free
urine that was negative for nitrite with the Chemstrip. It pro-
duced a nitrite concentration of 3640 IJg/mL.
Background nitrite concentration
in drug-negative specimens
In order to assess background levels of nitrite
in urine specimens for workplace drug testing,
specimens which were initial test negative were
evaluated. From among 200 specimens which
were tested by the Chemstrip, 15 were selected
as producing the most color on the Chemstrip
(Note: none of the 200 produced the typical
intense pattern of nitrite adulteration). These
specimens were stored at room temperature
for 2 weeks, and then tested for nitrite concen-
tration. They were held an additional 6 days
and retested. This process, although uncharac-
teristic of holding times and conditions for
employment testing specimens, was used to
represent an extreme circumstance in the
amount of background nitrite that might be
found in a negative workplace drug-testing
specimen. The data are displayed in Table IV. On
the first test (2 weeks from collection), the
group averaged 50.2 IJg/mL with a range of
6.2-128.1. The data on the retest were very
similar. The maximum nitrite concentration
obtained was 129.1 IJg/mL, which was the
highest concentration obtained in the entire
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