USDTL Nails Toxicology🔗

Name	USDTL Nails Toxicology (Maternal) (Nails)
Table Name	`bio_bm_biosample_nails_results; bio_bm_biosample_nails_type`
Construct	Drug Panel, Environmental Exposure
Study Visits	V01, V02
Type	In-person Biospecimen collection (Parent on Self; 5 min)
Quality Control	Examine assay ranges and categorical versus continuous measures

Workflow & Screening Updates

As of November 2025, USDTL no longer assayed sufentanil in the nail samples.
As of July 1, 2024, the nail processing workflow was updated to optimize specimen use and allow confirmation testing for low sample quantities. Prior to this update, remnants of ELISA extract were not used for confirmation when specimens had insufficient sample.

Continuous Variables

Continuous variables should be interpreted with caution based on limits of quantification (LOQ), i.e. the minimum concentration at which metabolites can be reliably quantified. See Urine Assay Thresholds for Analytes.

Large Gaps Between Collection and Analysis Dates

A substantial number of samples show unusually long intervals between collection and analysis (e.g., over 100–300 days, compared to the 30-day limit specified by internal SOPs). We are working to determine whether this reflects a data entry or site-level issue and will provide an update once more information is available.

Interpretation of “QNS” in Confirmatory Results When a Positive Is Expected

In some cases, a specimen’s initial test meets the threshold for a positive result, but the confirmatory result is reported as “QNS” (Quantity Not Sufficient). This occurs when there is not enough specimen to conduct a confirmatory test or a confirmatory test must be repeated (following quality control procedures, e.g. unacceptable chromatography, poor recovery, or when a sample result is <5% of the previous specimen), but insufficient sample remains to complete the repeat test. Because the results could not be validated, this should be treated as a true quantity insufficiency.

Instrument Details🔗

Nail processing workflow

For the USDTL assay, fingernail and toenail specimens are sorted by weight, and those weighing at least 20 mg undergo ELISA screening, followed by LCMSMS confirmation for presumptive positives, each requiring an additional 20 mg. If insufficient specimen remains for LCMSMS, the remnant ELISA extract is used for confirmation.

Based on the predefined thresholds (see Nail Assay Thresholds below), a confirmatory test result for any substance analyte is determined to be positive, negative, or invalid (QNS i.e. quantity not sufficient). Substance analytes (e.g. Amphetamine/c_amp_n) are grouped into different classes by analyte screening tests and confirmatory tests (see Mapping from Class to Screening & Confirmatory Tests).

The detection window for all analytes is 3-6 and 10-14 months for finger and toe nails, respectively, with the exception of Ethyl glucuronide (finger nails: 3; toe nails: no consensus). "Cutoff" is the threshold to classify results as positive or negative for an analyte.

Analytes	LOD (pg/mL)	LOQ (pg/mL)	Cutoff (pg/mL)
Amphetamine / Methamphetamine	20	40	100
MDA / MDMA / MDEA	20	40	100
Carboxy-delta-9-THC	0.01	0.02	0.05
Cocaine	20	40	100
Cocaethylene / Benzoylecgonine / Norcocaine	10	20	50
6-MAM	20	40	100
Codeine	20	40	100
Hydrocodone	20	40	100
Hydromorphone / Morphine	20	40	100
Norhydrocodone	8	16	40
Fentanyl / Norfentanyl / Alfentanil / Acetyl Fentanyl / Acetyl Norfentanyl	2	4	10
Sufentanil	1	2	5
Norsufentanil	2	2	5
Tramadol	200	400	500
Ethyl glucuronide	4	8	20
Nicotine / Cotinine	20	40	100

Final results for each substance follow these rules:

Positive results: If any confirmatory test for a substance analyte (e.g., Amphetamine/c_amp_n) is positive based on predefined thresholds, then the corresponding class-level (c_any_stim_n) and overall sample-level (c_any_specimen_n) results are also positive.
Negative results: If all confirmatory tests for analytes in a class are negative, then the class-level result is negative. If all classes are negative, the overall sample-level (c_any_specimen_n) result is negative.
Invalid results: If any confirmatory test for a substance analyte is invalid, then the corresponding class-level and overall sample-level results are also invalid.

Level	Result Type	Example	Possible Values
Specimen	Confirmatory results (presence of any analyte)	`c_any_specimen_n`	`1`=positive `0`=negative `3`=invalid
Class	Confirmatory results (presence of any analyte in class)	`c_any_stim_n`
Analyte	Screening results	`s_amp_n`
	Confirmatory results	`c_amp_n`	concentration value; -999
	Confirmatory results - categorical	`c_amp_n_cat`*	`1`=positive `0`=negative `3`=invalid `4`=screen negative

*Note: Categorical confirmatory test variable for alcohol follows a different convention and is c_ethanol_n.

Bandoli, G., Anunziata, F., Bogdan, R., Zilverstand, A., Chaiyachati, B. H., Gurka, K. K., Sullivan, E., Croff, J., & Bakhireva, L. N. (2024). Assessment of substance exposures in nail clipping samples: A systematic review. Drug and Alcohol Dependence, 254, 111038. https://doi.org/10.1016/j.drugalcdep.2023.111038

Sullivan, E. L., Bogdan, R., Bakhireva, L., Levitt, P., Jones, J., Sheldon, M., Croff, J. M., Thomason, M., Lo, J. O., MacIntyre, L., Shrivastava, S., Cioffredi, L.-A., Edlow, A. G., Howell, B. R., Chaiyachati, B. H., Lashley-Simms, N., Molloy, K., Lam, C., Stoermann, A. M., … HBCD Biospecimens Workgroup. (2024). Biospecimens in the HEALthy Brain and Child Development (HBCD) study: Rationale and protocol. Developmental Cognitive Neuroscience, 70(101451), 101451. https://doi.org/10.1016/j.dcn.2024.101451