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Decreased signal in Emit assays of
drugs of abuse in urine after ingestion of aspirin:
potential for false-negative results.
Wagener RE, Linder MW, Valdes R Jr
Department of Pathology, University of Louisville School
of Medicine, University of Louisville Hospital, KY
40292.
During routine drug analysis with the Syva d.a.u. Emit
immunoassays we observed a high frequency of urines with
lower rates of changes in absorbance (delta A R) than
the rate for a drug-free urine calibrator. Many of these
urines contained salicylates. Among 40 urines with
apparent salicylate concentrations between 15 and 420
mg/dL tested for benzoylecgonine (BE), 20 had delta A R
< -4 (range +2 to -28 mA/min). The rates decreased
with increasing salicylate: delta A R = -0.057 x (salicylate,
mg/dL) -0.22 mA/min (r = 0.85, n = 40, P < 0.01).
Urines from 100 control subjects (no salicylate) had
mean +/- SD delta A R values of -1.05 +/- 2.2 mA/min
(range +3 to -7; only two were < -4 mA/min). Although
direct addition of salicylic acid (200 mg/dL) to urine
specimens did not reproduce the negative bias, ingestion
of aspirin (acetylsalicylic acid) did by -0.09 mA/min
per 1 mg/dL (72.4 mumol/L) salicylate. Negative biases
observed for other Emit d.a.u. assays after salicylate
ingestion lead us to conclude that ingestion of
therapeutic doses of aspirin may cause false-negative
results for drug screens in urines by this technology.
PMID: 8149618, UI: 94199824
|
|
|
Decreased signal in Emit assays of
drugs of abuse in urine after ingestion of aspirin:
potential for false-negative results.
Wagener RE, Linder MW, Valdes R Jr
Department of Pathology, University of Louisville School
of Medicine, University of Louisville Hospital, KY
40292.
During routine drug analysis with the Syva d.a.u. Emit
immunoassays we observed a high frequency of urines with
lower rates of changes in absorbance (delta A R) than
the rate for a drug-free urine calibrator. Many of these
urines contained salicylates. Among 40 urines with
apparent salicylate concentrations between 15 and 420
mg/dL tested for benzoylecgonine (BE), 20 had delta A R
< -4 (range +2 to -28 mA/min). The rates decreased
with increasing salicylate: delta A R = -0.057 x (salicylate,
mg/dL) -0.22 mA/min (r = 0.85, n = 40, P < 0.01).
Urines from 100 control subjects (no salicylate) had
mean +/- SD delta A R values of -1.05 +/- 2.2 mA/min
(range +3 to -7; only two were < -4 mA/min). Although
direct addition of salicylic acid (200 mg/dL) to urine
specimens did not reproduce the negative bias, ingestion
of aspirin (acetylsalicylic acid) did by -0.09 mA/min
per 1 mg/dL (72.4 mumol/L) salicylate. Negative biases
observed for other Emit d.a.u. assays after salicylate
ingestion lead us to conclude that ingestion of
therapeutic doses of aspirin may cause false-negative
results for drug screens in urines by this technology.
PMID: 8149618, UI: 94199824
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