Effect of Freezing on the Concentration of Drugs of Abuse in Urine

Abstract

Benzoylecgonine, 11-nor-delta 9-tetrahydrocannabinol-9-carboxylic acid (THC-acid), phencyclidine, codeine, morphine, amphetamine, methamphetamine, and lysergic acid diethylamide were dissolved in urine, stored frozen in plastic tubes at -16 to -18 degrees C, defrosted, transferred to other tubes, and analyzed by gas chromatography/mass spectrometry (GC/MS); no significant loss of compound was observed, except for THC-acid, which showed an average loss of 11%, ranging from 0 to 34% of the total concentration. The loss is attributed to the decrease in solubility of the compound and to adherence to the side of the container during freezing.

Stability of pain-related medications, metabolites, and illicit substances in urine

“…In contrast, a study by Dugan et al found cTHC to be within 25% of the original concentration after 12 months in urine stored at −20°C [7]. Paul et al found a decrease in cTHC after frozen storage for 45 days, but the average decrease was only 11%, ranging as great at 34% [6].…”

“…However, there has not been a comprehensive study conducted to determine the stability of medications, metabolites, and illicit substances commonly requested for testing by physicians treating patients with pain and pain-related disorders. See Table 1 for a summary of the extant literature [5][6][7][8][9][10][11][12].…”

“…These studies have shown that specimens frozen at −20°C and those stored at +4°C are stable over a period of months [5][6][7][8][9]11]. Most often, specimens sent to reference laboratories are stored at +4°C because freezing and then thawing large numbers of urine specimens is impractical.…”

Issues Affecting Interpretation: Stability and Artefacts

“…THC-COOH appears to be stable in spiked samples stored in silanised glass at -20°C for long periods of time (Levine and Smith 1990;Paul et al 1993). However, urine is usually collected in plastic containers where an adsorptive loss may occur; also, adsorption on borosilicate glass surfaces has been reported (Paul et al 1993).…”

“…However, urine is usually collected in plastic containers where an adsorptive loss may occur; also, adsorption on borosilicate glass surfaces has been reported (Paul et al 1993). The lower solubility of THC-CCOH in urine decreases at both a lower temperature and higher salt concentration, promoting adsorption on container walls.…”