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Ask Dr. D. Love Your Own Question
Dr. D. Love
Dr. D. Love, Doctor
Category: Drug Testing
Satisfied Customers: 18654
Experience:  Family Physician for 10 years; Hospital Medical Director for 10 years.
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We monitoring health care professionals and had a urine drug

Customer Question

We monitoring health care professionals and had a urine drug screen come back positive with a creatinine of 42. When it was sent out to the second lab for confirmation, the creatinine level was reported at 57. When we questioned the toxicology supervisor at the first lab she told us that creatinine levels can change over time in a sample. Is this true? If so, what causes the change? If so, are there studies that support this that you could direct me to? Additionally, we have noticed that some of our participants have creatinine levels that are very similar. As we track them, we are looking for a policy to determine when to request visually witness collections. Should it be if there are 2 exact creatinines in a row or 2 of the same within a month or 3 similar with X time frame?: Any help you could give would be appreciated.
Submitted: 1 year ago.
Category: Drug Testing
Expert:  Dr. D. Love replied 1 year ago.

The issue in this situation is not whether the creatinine level actually changes, but whether the test result changes. Assuming that the urine specimen is properly stored, it will not have significant changes over time.

For any lab test, though, there is some variability in the results, even if the exact same specimen is tested multiple times. For screening methodologies, the tests are typically less reproducible, which means that there can be greater variability in the results that can be obtained from each specimen. If the result from a scsreening test is then repeated by the lab, using a methodology that is more accurate, then the lab result is typically much more reliable, so should be the creatinine level that should be used in any decision making.

There are many different brands of tests on the market, but the package insert to whichever brand of test is being used to perform the screen should include documentation of the variability that is seen with that test. Your lab personnel would be able to either review the insert or provide you with the insert, and that would be the best documentation of the variability, rather than a clinical study in the medical literature.

As for when to witness a collection, there are no studies that look at whether there should be concern about recurrent similar values on consecutive specimen. The studies have looked at the threshold of creatinine that should raise concern and justify a witnessed collection. There are varied recommendations, but part of that is the level of acceptance intrinsic to the recommendation. When we define any normal range, it is usually the range that encompasses 95% of the normal population. So, about 5% of normal people will have a result outside the normal range. In studies that have looked at traditional determinations of the normal range for urine creatinine, the threshold that would justify a witnessed collection would be a level of 45 mg/dl. However, there also are recommendations that the threshold should be 20 mg/dl, including federal guidelines. These lower thresholds are not based on studies that show a different normal range, but instead reflect a recognition that many normal people will be slightly outside the normal range, and a level below 20 mg/dl will identify a larger percentage of people that are intentionally attempting to dilute the urine. It is not that either threshold is right or wrong, but the decision of which threshold you want to follow will reflect your goals of testing. If you want to be more likely to detect everyone that is trying to dilute the urine, even if you need to witness far more normal people, then using the threshold of 45 mg/dl would be appropriate. But if you would rather limit the witnessed collection of normal people, then it would be appropriate to use the federal 20 mg/dl threshold.

If I can provide any clarification, please let me know.

Customer: replied 1 year ago.
if I understand what you are saying if a lab tests a specimen on day one and then on day 5 or day 10 tests the same specimen using the same methodology and same equipment the creatinine level would be the same, but if they tested in on those sames days using a different methodology the creatinine may be different? Is there a calibration involved in creatinine calculation that could cause a variable of 15? My question is, if in one test a person gets a dilute screen because their creatinine is < 20, but if tested by a different lab or possibly a better methodology (LCMSMS or GCMSMS) their screen may not actually be dilute. Could this be possible? Should the participant have the right to request the specimen be retested on a different methodology?
Expert:  Dr. D. Love replied 1 year ago.

Even if the same methodology is used on different days, you may get a variable result, and the extent of that variability is dependent upon the specific methodology, with the screening tests having the greatest amount of variability. The amount of variability would be stated in the package insert, but for a screening test, it would easily include a variability of 15.

Regardless of which threshold that you select, when the screen shows a level of creatinine that is considered too dilute, the testing by the better method in the lab may indicate that it is not dilute, so yes it is possible. The accurate test in the lab does not need to be a chromatography based test, but the chemistry analyzer in the lab will be more accurate than the screening test.

If you are using the screening creatinine test to determine whether to perform a witnessed collection, it is not reasonable for the participant to have the right to request a confirmatory methodology, because the result would not be available in a timely manner. However, if the creatinine level is being used to identify individuals that are intentionally trying to dilute the urine and there will be any adverse action taken against the individual based upon that creatinine level, then the participant should have the right to request that the specimen be retested via the confirmatory methodology, and then the result of the confirmatory test would be the basis for any adverse action.

Expert:  Dr. D. Love replied 1 year ago.

To complete the comment on the lab measurement of creatinine. The method that is used by several reference labs is an enzymatic assay, not any method that is based on chromatography. But this chemistry analyzer will be more accurate for the measurement of creatinine compared to the screening test.

If I can provide any further information, please let me know.