FAQ


There are many questions frequently asked by our clients. We hope you find the following questions and answers of use.

SAMPLE VALIDITY AND ADULTERATION: pH- CREATININE – SPECIFIC GRAVITY – OXIDANTS

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Why is creatinine measured? What does it mean?

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Creatinine is an indicator of sample validity. Creatinine is a natural by-product of protein metabolism in the body, and it is generally produced at a constant amount daily, which differs for each individual. It is always present in the urine if the kidneys are working properly. If a person is eliminating a lot of water, the creatinine will become more dilute temporarily. If a person is dehydrated, the creatinine will become more concentrated. But the amount eliminated will be relatively constant from day to day. For instance, carboxy-THC concentrations are frequently normalized to creatinine concentrations so that fluctuations in urine concentration are minimized. If a patient substituted water for his urine sample, there would be no creatinine, and the sample would be considered not valid. 20 mg/100 ml is the low end of the reference range. Specimens with a lower creatinine may also be valid, but may require closer attention.

Does a low creatinine value indicate dilution or attempted flushing of system?

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While most patients have creatinine values greater than 20 mg/100ml, values less than that are not uncommon and occur naturally in some people. Low creatinine may not be a concern until it drops below 10 mg/100 ml. Then it is worthwhile to check specific gravity. If the specific gravity is normal (greater than 1.003) the sample is considered to be valid .

What is Specific Gravity?

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Specific gravity indicates the weight of a ml of urine relative to water. (1.000 g per ml) If the urine sample was produced by the kidneys, and the kidneys are working properly, there will always be dissolved salts in the urine, and that increases the weight of the urine. A urine sample is considered valid if the specific gravity is greater than 1.003.

Does drinking a lot of water really affect urine drug tests?

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Drinking a lot of water can temporarily dilute urine for a short period of time. If a drug or metabolite is excreted in small concentrations, near the cutoff, it is possible to cause a negative screen. For instance, with a 50 ng/ml cutoff for carboxy-THC, a patient with a metabolite concentration of 52 ng/ml might be able to dilute their urine to 49.2, and have good fortune on that particular screen. However, a person with 5000 ng of oxycodone with a 100 ng/ml cutoff will not significantly change their screening outcome by excessive ingestion of water.

Do commercial ‘cleansing’ products really affect drug screening?

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Products ingested orally do not alter the outcome of drug screening. Acidic products can increase the rate of clearance of some drugs, like amphetamine, but they do not affect any of the tests. Products added to the urine sample can drastically change screening outcomes by chemically destroying the drugs and metabolites present in the specimen. Observed collections eliminate this problem. Observed collection is the only way to assure that an outside sample has not been substituted for one provided by the patient.

Does high pH indicate an adulterated urine sample?

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Urine samples, on standing at room temperature or at elevated temperatures during shipping, may display a gradual increase in pH to around 9. This is normal. A pH of 10 or more is suggestive of adulteration, but, addition of agents to change the pH of the specimen also change the color and appearance of the specimen, and the specimen may have an unusual odor. The laboratory staff are very careful to watch for these signs.

Does candy or gum affect the outcome of oral fluid screening?

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Food items like this which contain sugar can, in the presence of bacteria or yeast, produce sugar by fermentation, and produce high concentrations of alcohol.

DRUG SCREENING, CUTOFF CONCENTRATIONS, POC DEVICES

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Why are cutoff concentrations used? Are values below the cutoff valid?

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Cutoff concentrations are generally accepted in the industry and are chosen to maximize the number of true positive samples, while minimizing the number of false positives. In this way, the maximal number of drug users are detected, while reducing as much as possible false positive screens which require needless confirmation. It is accepted laboratory procedure to report values less than the cutoff as negative. While values less than the cutoff may be real, the convention is to consider them negative. Calibrations, quality control and confidence are established for the cutoff concentrations.

Why do some specimens screen positive but not confirm?

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The preliminary screening, whether POC or in the laboratory, is accomplished by using antibodies to the drugs. While the manufacturers take great care to make the antibodies as selective as possible, sometimes other compounds in the specimen will cross-react and cause a false-positive screen. Most of the time the preliminary screening is quite accurate. But high concentrations of other prescribed medications, or other non-prescription agents may cause a positive screen reaction. This is why confirmatory analysis is essential. In that process, specific chemical compounds are uniquely identified and quantitated. The preliminary screen is just an initial snapshot to provide guidance in confirmatory analysis.

Can you distinguish between actual ingestion of a drug versus the addition of some crushed tablet to a urine sample?

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It is difficult for a lay person to know how much tablet material to add to a sample. The presence of an extremely high parent drug concentration and the absence of any metabolites in a urine sample might be a indicator of such adulteration, and would require careful examination.

Are POC cups accurate?

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Generally, yes. But they are made as guidelines- quick snapshots. Their problem is twofold. First, other compounds may cause a false positive with them occasionally. Second, if drugs are present very near the cutoff, they may read positive or negative, and only LC/MS/MS confirmation can truly establish the presence or absence of the drug.

Why do results sometimes come back as ‘QNS’?

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This happens when these is not sufficient sample for analysis in the oral fluid tube or the urine cup. Most of the time this is due to leakage of the specimen container which, in turn, is frequently due to incomplete closure of the top or lid.

Does the presence of bacteria or mold in the sample affect testing?

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Bacteria cause a problem only with particular analytes. For instance, bacteria can destroy the alcohol metabolite ethyl glucuronide (EtG). This is why another metabolite (EtS) is also measured, because it is not affected by bacteria. Mold contamination in a sample where sugar is present (urine of a diabetic, patient, or oral fluid obtained after sucking hard candy) can result in the production of alcohol- by way of fermentation of the sample. Alcohol concentrations higher than the fatal range can be observed in these cases.

CONFIRMATION

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Why is LC/MS/MS a better confirmation technique than GC/MS?

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Gas chromatography/mass spectrometry (GC/MS) requires the drugs of interest to be put in the gas or vapor phase. This requires heating to very high temperatures. Sometimes it is additionally necessary to treat the sample with other chemicals (derivatizing agents) in order to get the drugs sufficiently able to be volatilized. This can result in loss of much of the analyte due to chemical instability at high temperatures. Thus much drug can be lost, and limits of detection are compromised. In addition, once volatilized into the gas phase, many drugs take a long time to go through the column of the gas chromatograph. Thus run times are long, and again much compound can be lost to thermal instability. In liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) the compounds travel underivatized through a chromatography column in solution at or near room temperature. Nothing has to be volatilized, there is no degradation due to heat, and the run time through the columns is very fast-no more than 5 minutes. The LC/MS/MS is much more sensitive than the GC/MS.

Why are screens sometimes positive, but confirmations negative?

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Two possible reasons emerge for this. First, drugs may be metabolized to a number of different compounds which retain the ability to be recognized by the screening antibody, and screen positive, while the target drug or metabolite of confirmation is far below the cutoff concentration. Secondly, other substances or drugs may be cross-reactive to give a false positive screen, while the target drug itself is not present in the specimen.

Why does clonazepam in urine screen negative for benzodiazepines, yet confirm positive?

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Clonazepam is present as a metabolite in urine. It does not react well by the commercially- available screening reagents. It is not recognized well by the benzodiazepine antibody. Therefore, clonazepam metabolite is quantitated separately by LC/MS/MS to assure that it is detected at a very small concentration.

Why do I get positive buprenorphine screens that do not confirm?

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There is not a definitive answer for this. The buprenorphine antibodies in the screening reagent are very sensitive and may detect metabolic products or large concentrations of other drugs that cause the chemistry to give a positive screen. Yet the target drug and its primary metabolite are not actually present at sufficient concentration to be above the confirmation cutoff value.

CONFIRMATION IN ORAL FLUID VS URINE

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How do windows of detection differ between oral fluid and urine?

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Windows of detection are generally shorter in oral fluid than in urine. The windows more closely parallel windows of detection in blood. Blood concentrations of many drugs fall rapidly because of metabolism by the liver or elimination by the kidney. Since parent drugs, rather than metabolites, are measured in oral fluid, the life-time of parent drugs may be shorter. The drug metabolites continue to be excreted in the urine, where they are concentrated by the kidney and collect in the bladder for hours. Thus, urine may provide a longer window of detection for drug metabolites.

If a person takes their medication every day, will it show up in oral fluid and in urine?

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Generally, yes. For the most part, a person on daily regular medication will show positive analyses for those drugs in oral fluid and in urine. Patients using drugs only occasionally or on a ‘prn’ basis may, or patients who miss doses of drug, or patients nearing or exceeding the end-life of a drug patch may show negative results for those drugs.

Why do patients taking hydrocodone sometimes show negative oral fluid analysis?

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The time-course of appearance and disappearance of hydrocodone in oral fluid after dosing in controlled laboratory settings has not been studied. Since the parent drug is quantitated in oral fluid, if that drug is metabolized or eliminated very quickly in a particular patient, it may not reach sufficient concentrations in oral fluid for detection. Yet the drug metabolites would end up concentrated in urine. Whereas oral fluid windows of detection more closely parallel windows of detection in blood, the concentrations achieved can be quite different. Oral fluid concentrations of some drugs are considerably lower than those found in serum. The factors underlying this are unclear. We have observed that in a few patients, hydrocodone windows of detection are small.. Analysis of a urine sample will always demonstrate the drug if it is present.

What other rapidly metabolized drugs can be cleared quickly from oral fluid and may result in negative screens?

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In our observations: oxymorphone, alprazolam and lorazepam.

Would you recommend a urine drug test over an oral fluid drug test?

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If a patient is regularly taking medication on a daily basis, either test should give satisfactory results. The oral fluid analysis will provide a large menu of parent drugs, and demonstrate recent use of marijuana and alcohol. Urine offers a large menu of drug metabolites and many parent drugs with a somewhat longer window of detection, especially for alcohol metabolites. Having either test available provides a choice to more closely examine the dynamic motion of the drug through the body.

COMPLIANCE

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Does detection of metabolites at low concentrations in oral fluid or urine indicate compliance?

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The demonstration of these metabolites does indicate that the drug was recently ingested. But since the specimen collected just represents one point in time of a concentration vs time continuum, nothing can really be said about compliance. We do not know when the drug was ingested or how much was taken, all factors in compliance. We do know however that the drug was ingested at some point.

Can you tell if a patient is taking their medications as prescribed from the quantitation results?

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Generally yes, but concentration ranges cannot be specified. Different pain patients are on vastly different dosages of the same drugs. One patient might routinely take a dose of morphine which would be fatal to a naïve patient. As mentioned earlier, we generally do not know when the last dose of medication was taken, or how large the dose was. A particular quantitation result may superficially appear to be consistent with a clinical dose of a drug, but in realty may be the value much longer after an abuse dose of the drug. Exceedingly high drug or metabolite concentrations can be flagged as suspicious, as can be the absence of required drugs. The presence of non-prescribed drugs can also be of value in evaluation of compliance.

Can liver disease affect drug elimination?

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Yes. Cirrhosis or damage from Hepatitis-C can delay drug metabolism significantly.

How will dialysis affect drug elimination?

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This is a very complex issue, which depends on how widely the drug is distributed (what percentage is actually in the circulation), and how quickly drug in the tissues equilibrates with drug in the circulation. It would be best to consult with the patient’s nephrologist or renal specialist to clarify this question for each individual patient.

SPECIFIC DRUGS

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How do we interpret EtG and EtS concentrations in urine?

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This indicates that there has been some exposure to alcohol in the past few days. Since we have only one point in time, and since sources of alcohol exposure are so many, we do not attempt to pinpoint the source or intent of alcohol ingestion. The finding of these compounds in urine demonstrates an exposure to alcohol.

How do we interpret the presence of 6-Acetylmorphine (6-AM) in oral fluid or urine?

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Generally this is interpreted as administration of heroin, especially if the concentrations are large. It has been reported however that very small amounts of 6-AM can be present with very high concentrations of morphine in urine. As a contaminant, 6-AM is present much in less than 1 percent of the morphine concentration, so this possibility must be examined before concluding heroin use.

What change in carboxy-THC concentration constitutes ‘new use’ of marijuana?

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Currently this is a qualitative assessment, generally made by criminal justice personnel, based upon a significant rise in creatinine-normalized carboxy-THC confirmation values for a single patient under ongoing observation.

OTHER MATRICES

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Why doesn’t Forensic Laboratories perform drug analysis in hair?

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Too many factors are unknown, and we feel there is insufficient foundation for the weighty decisions being made as a result of these analysis. Specifically,
• Dose/hair-content relationships have not been established.
• The significant role of hair pigmentation in drug accumulation has not been quantitated.
• There is not an acceptable source of quality control material, where known drug doses have been administered to humans, and hair samples made available. Soaking of hair in drug solutions (external application) is not equivalent to drug ingestion.
• There is not a widely used and accepted proficiency testing program.