THE CREATININE LEVEL
The urine creatinine level is used in two ways; first as an indicator of specimen validity
and second in determining “new use” of marijuana.
Individuals being drug-tested and those responsible for urine testing programs are aware
that specimens submitted for testing are vulnerable to adulteration (tampering).
Although collection procedures are in place to ensure specimen integrity, donors have
demonstrated ingenuity in their efforts to defeat the testing process. Possible methods
of avoiding drug-use detection include the addition of adulterants to the specimen, the
substitution of someone else’s urine and specimen dilution. Both specimen adulteration
and specimen substitution are difficult to accomplish during an observed collection. The
presence of adulterants in a urine specimen has the same implications as the presence
of drugs. As a result, the most common way to mask drug use is by “internal” dilution
(Flushing). This is done by excessive water consumption, and/or taking diuretics such
as herbal teas.
Creatinine as an Indicator of Normal vs. Abnormal Urine
Specimens
Creatinine is a naturally eliminated in the urine at a relatively stable rate. Therefore, the
urine creatinine level indicates the urine concentration. Most normal urine samples will
have a creatinine value between 20-350 mg/dL (milligrams per deciliter). A specimen
with a urine creatinine level less than 20 mg/dL is considered “dilute”. Less than 2% of
people normally produce a urine sample with a creatinine level under 20 mg/dL. Among
those urine samples submitted for employment related drug testing, about 2% (slightly
higher than normal) are dilute. Finally, 8% of those urine specimens submitted to
Norchem for court-directed drug tests have a creatinine level under 20 mg/dL.
Drugs are present in the urine in proportion to the urine concentration. When the urine is
less concentrated, there is a lower concentration of drugs. When the urine is too dilute,
a negative result does not assure non-drug use. Norchem measures the urine creatinine
level on every specimen we test and we report when the specimen is too dilute. We
recommend that negative drug test results be disqualified when the specimen has a
creatinine level less than 20 mg/dL. Conversely, a positive result on a dilute specimen
would not be disqualified, because this indicates that the drug was in such high
concentrations that it was detected even with a low urine concentration.
The most common way for a donor to produce a urine specimen with a creatinine level
below 20 mg/dL is to drink large quantities of liquid and/or take diuretics prior to
providing a specimen. Commercially available products that are marketed as aids in
“beating the drug detection system,” such as Clean-Free, SafeTest, Naturally Clean
Herbal Tea and Goldenseal, can be effective because they contain natural diuretics
and encourage additional liquid consumption.
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Some donors deliberately drink large quantities of fluids for medical reasons or because
they think it is a healthy habit. If a donor consistently provides a dilute specimen they
should be reminded that it is their responsibility to provide a specimen suitable for testing
and failure to do so might be considered “Refusal to Test”. They should reduce their
liquid consumption and limit their use of caffeine and herbal teas. Most people will
comply unless they are attempting to mask their drug use.
The best way to minimize the percentage of dilute urine specimens is to use a random
collection program. Unannounced specimen collection presents the donor with little time
to prepare. Another good practice is to get a first morning “void” if possible, as this
specimen often is more concentrated. People who dilute their urine by drinking large
amounts of liquids cannot continue this practice indefinitely.
The Role Creatinine Plays in Determining New Use of Marijuana
Marijuana (THC) can persist in the urine long after use; from two days for the occasional
user to six weeks for the chronic user. There is often a need to determine if a current
positive THC result indicates new marijuana use or a previous use. In principle, the THC
level should decrease over time following the last use. However, the THC level also
depends upon the urine concentration. In order to handle this complication the THC
level is divided by the creatinine level (CR). The THC/CR ratio should decrease over
time when there is no new use. The rule-of-thumb is that when comparing two results,
the THC/CR ratio should decrease by 50% every 2-10 days depending on the individual.
A light-infrequent user will decrease faster than a heavy-frequent user.
It is important only to compare results derived from the same test method, either
compare EMIT values with EMIT values, or compare LC/MS/MS values with LC/MS/MS
values.
The following table shows data from one donor who provided three specimens on three
different dates.
Specimen:
Collection Date:
THC level (ng/ml):
Creatinine level (mg/dl):
THC/CR Ratio :
A
08-02-11
350
52
6.7
B
08-10-11
450
150
3.0
C
08-20-11
180
20
9.0
Specimen A has a THC/CR ratio of 6.7 compared to Specimen B with a ratio of 3.0.
Over this time period, the decline is consistent with abstinence. However, new
marijuana use is indicated in the time period between Specimen B and Specimen C: the
THC/CR ratio increased from 3.0 to 9.0.
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