Quantity Not Sufficient

USDTL Research

Quantity Not Sufficient

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The dreaded "QNS" explained.

by Douglas Lewis, D.Sc. 

“Quantity not sufficient – No result available” is probably the worst outcome that can occur when a hair, fingernail, or toenail specimen is submitted to USDTL for analysis. Everyone involved in the process, the donor, the collector, all laboratory personnel, and our Client Advocates are all disappointed, at best.

Everyone in the process wants a collected hair or nail specimen to produce a forensically valid result, not a QNS that sends us back to square one. What goes on in this whole process and how can QNS results be reduced or eliminated?

Begin with the choice of tests on the requisition form. Years ago, there was only one choice for testing hair specimens, the 5-panel "Drugs of Abuse" option. The specimen requirement was 100mg of hair, cut at the scalp, and extending 1½ inches in length. The visual was described as a ponytail the diameter of a standard #2 pencil. No one weighed their specimens prior to inserting the hair into its foil wrapper as balances were both very expensive and difficult to use.

USDTL, however, extended the testing menu by adding additional drugs and classes of drugs to reflect the changing usage both in professional and general drug using populations. The testing menu has grown to now include up to almost 20 drug classes and the alcohol biomarker Ethyl Glucuronide (EtG). We also have validated that nail clippings produce forensically defensible results for both drugs of abuse and EtG, giving collectors choice in keratinized specimens for long term drug and alcohol exposure.

The expansion of the panels requires more aliquots of the samples so that the sample requirement for a panel of up to 10 drugs remained at 100mg, and for EtG, add-ons and/or tests above 10-panel, 150mg of specimen is recommended.

These specimen requirements are the same for all keratinized matrices: hair, fingernails, and toenails. In our modern microprocessor age, accurate electronic gem scales are available for less than $50 through multiple on-line vendors, so collectors have a simple and accurate means to verify the weight of every specimen prior to sealing the specimen for shipment.

Why does USDTL need so much specimen? That answer involves four separate issues.

First is the number of screening assays that are run on the specimen. The more screening assays, the more specimen is required. Also involved is the fact that as panels get larger, the probability that a screening batch will fail due to a QC error rises. When a full batch fails, the batch must be fully re-run from the beginning, thus additional aliquots must be used.

Our second issue is our EtG assay which is done separately by LC/MS/MS. This means an aliquot is used to initially screen all of the EtG specimens, and then all of the presumptively positive specimens. The initial screening must be confirmed through a second aliquot and run again by LC/MS/MS. This process of screening plus confirmation routinely consumes 40 mg of specimen.

Our third issue is that as a Forensic Toxicology Laboratory, USDTL tends to receive high risk (non-workplace) specimens that have a very high positivity rate. We often have specimens that have four or more drugs that screen positive and require confirmation. Each confirmation requires a separate aliquot of the original specimen. Because of this,  high risk specimens go through a larger reduction in specimen quantity as they proceed through the confirmation process than lower risk specimens such as workplace specimens.

Our last issue is that, as a Forensic Toxicology Laboratory, we must reserve sufficient specimen, whenever possible for re-test at the subject’s request. The re-test is an important safeguard that we and our accrediting agencies find very important.

At USDTL, we appreciate how difficult collecting forensic hair and nail specimens can be. We do our best to perform the tests that you order on what we receive. Our best, however, must be within the requirements of our accrediting bodies and accepted forensic practice.

We will do all we can to assist you in making your specimen collections as successful as possible. If you remember that hair is just one keratinized matrix and that there are two others available to look at when one looks to be inadequate. Do not be afraid to explore fingernails and, if the fingernails are not adequate, look at the toenails. All three of these keratinized matrices can produce a long term look back with forensically defensible results.


Materials excerpted from USDTL’S Standard Operating Procedures Manual, FAQ’s and Personal Communications with hundreds of clients over 25 years.


Douglas Lewis is the founder, President and Scientific Director of USDTL where he oversees development of new matrices for use in diagnosing substances of abuse, such as: umbilical cord tissue used to determine substance exposure in newborns, and fingernails to determine alcohol biomarkers and substances of abuse. 



Published by: United States Drug Testing Laboratories on




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