William E. Schreiber - An Introduction to Testing for Drugs of Abuse

Dilution – the goal of this strategy is to dilute drugs in urine below the threshold for a positive result. This can be accomplished in several ways: (i) drinking an excess of fluids prior to collection, (ii) taking diuretics to flush drugs out of the urinary tract, and (iii) adding water or another liquid to the sample itself.

Assessment of specimen validity begins with measuring urine temperature, which should be 90–100 °F (32–38 °C) within 4 minutes of collection. The physical appearance is also evaluated for color and consistency, and any unusual odor is noted.

The following chemical tests are run on patient samples to detect tampering that may give a false result.

The Substance Abuse and Mental Health Services Administration (SAMHSA) has developed criteria for specimen validity in workplace drug testing programs. Dilute and substituted specimens are identified by comparing the values for creatinine and specific gravity ( Table 3.1). To label a specimen as adulterated, an abnormal pH or the presence of a known adulterant is required ( Table 3.2).

Table 3.1 Substance Abuse and Mental Health Services Administration criteria for labeling a urine specimen as dilute or substituted. a

aBoth criteria (creatinine and specific gravity) must be met.

Table 3.2 Substance Abuse and Mental Health Services Administration criteria for labeling a urine specimen as adulterated. a

aAny one criterion is adequate. Depending on how samples are tested, other adulterants may be detected as well.

Table 3.3 Substance Abuse and Mental Health Services Administration criteria for labeling a urine specimen as invalid. a

aIndividual laboratories may use different or additional criteria.

Specimens can also be deemed invalid in a number of situations ( Table 3.3). An invalid result may indicate specimen tampering, but other explanations are possible. A review of the patient's history and consultation with the laboratory may clarify the situation.

1 Allen, K.R. (2011). Screening for drugs of abuse: which matrix, oral fluid or urine? Ann. Clin. Biochem. 48: 531–541.

2 Bosker, W.M. and Huestis, M.A. (2009). Oral fluid testing for drugs of abuse. Clin. Chem. 55: 1910–1931.

3 Cooper, G.A.A., Kronstrand, R., and Kintz, P. (2012). Society of hair testing guidelines for drug testing in hair. Forensic Sci. Int. 218: 20–24.

4 Dasgupta, A. (2007). The effects of adulterants and selected ingested compounds on drugs‐of‐abuse testing in urine. Am. J. Clin. Pathol. 128: 491–503.

5 Verstraete, A.G. (2004). Detection times of drugs of abuse in blood, urine and oral fluid. Ther. Drug Monit. 26: 200–205.

1 Garg, U. and Cooley, C. (2019). Testing of drugs of abuse in oral fluid, sweat, hair, and nail: analytical, interpretative, and specimen adulteration issues. In: Critical Issues in Alcohol and Drugs of Abuse Testing, 2nd Edition (ed. A. Dasgupta), 405–427. Academic Press.

1 Clinical Drug Testing in Primary Care (2012). HHS Publication No. (SMA) 12‐4668. Rockville, MD: Substance Abuse and Mental Health Services Administration. https://store.samhsa.gov/sites/default/files/d7/priv/sma12‐4668.pdf.

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