What causes immunoassay interference in drug screen

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1 What causes immunoassay interference in drug screen Other non-specific, exogenous interferences can arise from aberrant assay reagent or equipment interaction with patient sample, dissimilar reactions for the standard matrix and patient sample, e.g., sample-induced changes in ph and ionic strength of the reaction mixture, or from pre-analytical variables affecting the sample analyte concentration by physical masking of the antibody label. 19. Management of Acute Coronary Syndromes in Patients with Diabetes. 7. Daher R, Haidar JH, Al-Amin H. Rifampin interference with opiate immunoassays. Clin Chem 2002;48: Cannabinoid NSAIDs (ibuprofen, naproxen) Controlled-exposure study of 60 subjects (510 specimens) 4. Changes to the Measurable Analyte Concentration in the Sample. 12. George S, Braithwaite RA. The effect of glutaraldehyde adulteration of urine specimens on Syva EMIT II drugs of abuse assay. J Anal Toxicol 1996;20: Wu AH, Forte E, Casella G, et al. CEDIA for screening drugs of abuse in urine and the effect of adulterants. J Forensci Sci 1995;40: Wu A, Schmalz J, Bennett W. Identification of Urin-Aid adulterated urine specimens by fluorometric analysis [Letter]. Clin Chem 1994;40: False-positive reports on urine drug screens by immunoassay are rare (strength of recommendation [SOR]: C, small controlled-exposure studies, small case series). Nonsteroidal anti-inflammatory drugs, fluoroquinolones, and Vicks Inhaler are most frequently implicated ( TABLE ). Ruling out a false-positive result requires confirmation with a more specific test, usually gas chromatography/mass spectrometry (GC-MS). A true-positive drug screen may occur in a urine specimen from a patient who legally or unknowingly ingests a product that is metabolized to a drug of abuse. Passive exposure to a substance is unlikely to cause a positive drug screen (SOR: B, small controlled-exposure studies). In immunoassays for drugs of abuse screening, false-positive interference may occur from medications or their metabolites that have similar chemical structures. 27. Substances that do not produce positive urine drug screens include passively inhaled crack cocaine or marijuana (unless "extreme"), and ingested products containing hemp or other common herbal preparations. 1, 2, 10. Increased EDTA concentration in the sample-reagent mixture due to insufficient sample volume causes chelation of Mg 2+ and Zn 2+ and can affect the activity of the alkaline phosphatase enzyme label used in chemiluminescence assays. Filling of EDTAsample tubes to 50% affects intact parathyroid hormone 47. Interferences that alter the measurable analyte concentration in the sample. COPD in Primary Care: Key Considerations for Optimized Management. Prozone is a specific type of interference found only in one-step sandwich assays with very high analyte concentrations. The analyte molecules, under this condition, saturate out all reagent antibodies, thus producing negative interference only. The best way to resolve prozone interference is to dilute the samples and rerun the assay. Other unsuspected binding protein(s) in the individual also can cause interference in immunoassay by interfering with the reaction between analyte and assay antibodies. In reagent-excess assays in which the two-site immunometric assay (IMA) is commonly used, there is an increased likelihood of a potential cross-reactant forming a bridge between the two antibodies. During the antigen-antibody interaction conformational changes to antigens, induced by antibodies, may alter the specificity of

2 antibodies. For these reasons there may be a higher prevalence of unpredictable crossreaction in IMAs compared with a single-site antigen-antibody reaction in reagent-limited assays. 21. Since the immunoreaction involves interaction between epitope of the analyte and the binding site of the antibody, any compound presenting a similar epitope may crossreact with the assay antibodies. The extent of interference from a cross reactant will depend on how similar its structure is to the analyte epitope. Competition assays, which use singleassay antibodies, suffer more from cross-reactivity interference than immunometric or sandwich assays, which use two antibodies. Bidirectional interference positive with certain analyte and interferent concentrations, and negative with other concentrations has been observed in some immunoassays. Use of monoclonal antibodies in modern immunoassays has improved assay specificity, reducing cross reactivity. Furthermore, serial dilutions of samples can resolve interference from cross reactants. Several controlled-exposure studies have shown that as little as 1 poppy seed muffin (about 15 g of seed) can produce detectable amounts of morphine and codeine by immunoassay as well as GC-MS. 1, 2. When interference is present it may be analyte-dependent or -independent. Analyte-independent interferences refer to the common interferences of haemolysis, lipaemia and effects of anticoagulant and sample storage, and are independent of the analyte concentration. Analyte-dependent interferences in immunoassays refer to interaction between constituents in the sample with one or more reagent antibodies. They include compounds with chemical differences but structural similarities that cross-react with the antibody, heterophile antibodies, human anti-animal antibodies, autoanalyte antibodies, rheumatoid factors and other proteins. Interference can lead to falsely elevated or falsely low analyte concentration depending on the site of the interference in the immunoassay reaction. The interference may result in discordant results for one or more analytes, and may be detected in one or more other assay systems for the affected analyte. The magnitude of the effect depends on the concentration of the interfering substance, but not necessarily in a directly proportional way. Interference affects a wide range of immunoassay analytes including hormones, tumour markers, drugs, cardiac troponin, and microbial serology. It may result in the misinterpretation of a patient's results from which the wrong course of treatment is given. 3. False-positive or false-negative values may arise, depending on whether the autoantibody-analyte complex partitions into the free or the bound analyte fraction. Regardless of whether a reagent-limited or reagent-excess immunoassay is used, interference from autoantibodies can occur in both formats. Autoantibodies to thyroid hormones have been reported in patients with Hashimoto's thyroiditis, Graves' disease, hyperthyroidism after treatment, carcinoma, goitre and nonthyroid autoimmune conditions. 52. Nature of Interferences Interfering, endogenous substances that occur in both healthy and pathological patient samples arise from properties of the specimen. The sample properties are unique to the patient and interference results from an interaction with one or more steps in the immunoassay procedure such that the measurable analyte concentration in the sample or antibody binding is altered ( Table 1 ). 19. Usually people try to cheat drug testing by three different ways: substituting their urine with synthetic urine or drug-free urine purchased from a clandestine source; drinking a commercially available product to flush out drugs; or adding an adulterant in vitro to the urine specimen after collection. Pain Management Antipsychotics, With Confirmation, Serum and Urine. HIV-1/2 Antigen and Antibodies, Fourth Generation, with Reflexes. Bloodworks Northwest performs DTT testing, as do other reference labs, but it's not routine in most hospital laboratory testing. "So hospitals with patients on daratumumab, when they have interference, will send the tests to us," says Dr.

3 Delaney. Over time, some hospitals may decide they don't wish to send out the samples and will bring the DTT protocol into the laboratory if they have the test volume and staff to do it. "But for many blood banks, the DTT chemical treatment is actually a reagent they have to make themselves, it has to be made fresh, and that's something most hospital blood banks are not interested in doing.". When crossmatching is attempted on patients who are taking daratumumab, explains Dr. Kaufman, the antibody screen looks for so-called unexpected (non-abo) antibodies in the patient's plasma, so the blood bank can ensure that donor red blood cells that are selected for a particular patient will survive normally when transfused to that patient. "The problem with daratumumab is you can't tell if there are antibodies hiding in the patient's plasma because all the testing to detect the antibodies comes out positive. Daratumumab can essentially mask the presence of one or more unexpected antibodies.". "One thing that was interesting is that we saw some positive DATs [direct. "The big challenge with daratumumab is that this drug is now being given to patients in every hospital everywhere. Yet the only way to know for sure if the patient is on daratumumab or another similar agent is for the provider to inform the blood bank." That's not something providers typically do. "They tell the blood bank very little. They prescribe a unit of blood or they order a type and screen, and they don't tell the blood bank what the patient is on. Nothing magical in that tube lets you know there's daratumumab there unless they tell you," Dr. Delaney says. Janssen has been active in working with blood bank leaders to solve the interference problem, she notes. "Most traditional chemotherapy drugs are chemical agents that are cell killers. They don't create this kind of interference, whereas the new class of cancer drugs, biologics, are antibodies that are directed at certain targets." problem," she says. The antigen used in the test is group specific and not species specific. Interference has been reported with this assay in patients suffering from Ehrlichia infections and Lyme disease. Drug Testing, General Toxicology (Blood, Urine, or Serum). The delay caused by daratumumab's interference with pretransfusion testing and crossmatching is not highly dangerous because the blood is normally not needed urgently. Multiple myeloma patients are mostly being treated as outpatients, not on an emergency basis, Dr. Kaufman says. "Usually they can wait, but sometimes patients come in fairly anemic, and it's a hassle. It's certainly a big inconvenience." However, the delays and consternation the interference causes are unnecessary, Dr. Delaney notes. "If the doctor tells the blood bank that the patient is on daratumumab, then the blood bank could have that information and know to use special testing protocols that get around the problem.". New York Blood Center received its first case with unknown daratumumab interference in June A large amount of testing was done on the initial case because the reactivity suggested an antibody to a high prevalence antigen. Based on the strength of reactivity, enzyme testing, and the lack of reactivity with cord RBCs, the first suspicion was a Knops antibody. "This was quickly ruled out, and uncommon specificities were investigated using rare RBCs," Dr. Westhoff says. "Only Lu(a b ) RBCs of the dominant In(Lu) type did not react, but the very rare recessive type of Lu(a b ) RBCs did react. The lab was perplexed because we couldn't believe the specificity could not be identified. It took two additional mystery samples to connect the common diagnosis of multiple myeloma.". Cytomegalovirus (CMV) and Epstein Barr Virus (EBV) PCR. Melanoma, BRAF V600E and V600K Mutation Analysis, THxID. Laboratory Corporation of America Holdings. All Rights Reserved. LabCorp and its Specialty Testing Group, a fully integrated portfolio of specialty and esoteric testing laboratories. Acid-Fast Bacillus (AFB) Identification, Sequencing and Stain, Paraffin Block. " Drug Testing, General Toxicology (Blood, Urine, or Serum). If the cancer treatment drug daratumumab were capable of deceptive intent, it might be accused of all

4 those ploys when it comes to interfering with blood transfusion crossmatching. The reason: For patients receiving daratumumab, marketed as Darzalex by Janssen Pharmaceuticals, antibody testing for transfusion is subject to erratic false-positives, often leaving transfusion services confused, uncertain, and on hold. Infliximab and Adalimumab Drug and Anti-drug Antibody Testing. Biologics have been around quite awhile but their toolbox keeps expanding, she points out, and the interference issue has added a new twist to cancer drug development. "Janssen didn't mean to develop a drug that did this. They just wanted a drug that's a blockbuster for myeloma. They've had to start learning about blood banking, so it's been a trial by fire. But they're really engaged in trying to figure out how to let labs handle patients who are on this drug, because they want the drug to be successful.". Chemistry and Immunoassay Analyzers for POC and Low-Volume Labs. Enzyme immunoassay (EIA) with indirect fluorescent antibody (IFA) titer on positives. Multiple myeloma affects a large number of patients; it is one of the more common blood cancers, Dr. Delaney points out. "When the FDA approved daratumumab, it meant that it moved out from the academic centers to wide availability. So community oncologists will now use the drug. It will become much more widespread than just an agent used at big cancer centers." problem," she says. For this reason, the AABB recommends that patients be tested before they begin daratumumab treatment. "This pre-testing, to ensure the patient doesn't have antibodies to blood group antigens before receiving the drug, sets the stage for the blood bank to be informed. They also can do an extended blood typing, sometimes by genotyping," she says. When the patient starts the drug and the next sample comes in, "the blood bank technologists look at the record and say, 'Ah, the patient is on daratumumab.'". Many of the medications reported to cause false-positive UDS results include a variety of antidepressants, which can be used for various indications. Of the selective serotonin reuptake inhibitors (SSRIs), sertraline has been reported to cause false-positive results for benzodiazepines and lysergic acid diethylamide (LSD), 1-4,9 and fluoxetine has been reported to cause false-positive results for LSD and amphetamines. 1,3,9 Bupropion and trazodone have likewise been reported to cause false-positive LSD and amphetamine results, with the interaction to the amphetamine assay credited to cross-reactivity with the agents' metabolites. 1-4,9 Additionally, numerous reports have found venlafaxine to cause false-positive phencyclidine (PCP) results. 2-4 While both venlafaxine and its active metabolite, O-desmethylvenlafaxine, are structurally dissimilar to PCP and have extremely low cross-reactivity (0.0125% and 0.025%, respectively), the concentrations of the two together have been hypothesized to cause the false-positive results. 2,4. Similarly, opiates can be at risk for false-negatives. Most immunoassay tests look for morphine, norcodeine, and codeine; thus morphine, heroin, and codeine can easily be detected. Hydrocodone and hydromorphone are metabolites of codeine and are rarely positive on immunoassay tests. Oxycodone, buprenorphine, and tramadol follow a separate metabolic pathway, and fentanyl may not be detected because it lacks metabolites. 1,4 To minimize the need for confirmatory testing, consider using morphine or codeine in high-risk patients. University of South Dakota School of Medicine Sioux Falls, South Dakota. Determining what OTC products patients are taking is very important when using UDS testing, as some OTCs may cause false-positive results. Antihistamines, analgesics, cough suppressants, and heartburn medications have been shown to cause false-positives in studies and case reports For patients being treated for attention-deficit/hyperactivity disorder (ADHD), UDS testing may also be recommended. Immunoassays test for amphetamines; thus, amphetamine, dextroamphetamine, and lisdexamfetamine products should return positive results for compliance testing if taken in the last 2 to 3 days. Illicit methamphetamine will

5 also show positive within the amphetamine immunoassay test. However, methylphenidate products do not cross-react with amphetamines and will commonly produce negative results, 8 although a false-positive result with methylphenidate has been seen in one pediatric case report. 1-2,8 If methylphenidate products are used, a GC-MS test should be routinely administered. False-negatives can occur when the urine drug concentration is below the threshold level set by the laboratory performing the test. 1,2 Dilute urine, the duration of time between ingestion of the drug and time of testing, and the quantity of the drug ingested may affect the occurrence of false-negatives. 1-2 While chronic marijuana use will show in the urine for weeks after heavy use, other medications and illicit drugs will only be present for 1 to 4 days, as shown in TABLE In addition to antidepressants, many antipsychotic agents have also been reported to cause false-positive results. Antipsychotics may be used to treat a variety of psychiatric disorders, with the secondgeneration antipsychotics (SGAs) used more frequently due to their more favorable sideeffect profile compared to the first-generation antipsychotics (FGAs). Of the SGAs, risperidone has been reported to cause false-positive LSD results; 3,9 quetiapine, falsepositive methadone and TCA results, which are attributed to quetiapine's resemblance in structure to methadone and TCAs. 2-4 Two case reports of accidental aripiprazole ingestion in pediatric patients resulted in false-positive amphetamine results. 10 Whether false-positives with aripiprazole may also occur in adults is uncertain. 10 The FGAs chlorpromazine, prochlorperazine, haloperidol, and thioridazine may all cause falsepositive LSD results. 3 Thioridazine may additionally cause false-positive amphetamine, methadone, and PCP results, and chlorpromazine cause false-positive amphetamine (due to similarities in structure) and methadone results Patients may purposefully attempt to hide positive screening results by adding contaminants to their urine that mask the presence of a drug, such as vinegar, soap, bleach, drain cleaner, eye drops, table salt, or ammonia. 5 Additionally, commercial products with the active ingredients peroxide (peroxidase), glutaraldehyde, sodium or potassium nitrite, and pyridinium chlorochromate could be used. 5 Changes in urine appearance, color, specific gravity, or ph may indicate the presence of a contaminant and should be checked. Patients may also drink an excessive amount of water (2-4 qt) or use diuretics to purposefully dilute their urine and the urine drug concentration to decrease the chance of detection. 5,6. When selecting an antipsychotic agent for high-risk patients, consideration should be given to using lurasidone, olanzapine, or ziprasidone when appropriate. Aripiprazole may also be a reasonable option in adults, as no reports have found false-positive results in this population. However, pharmacists should carefully consider the possibility of a positive result being false should one occur with a patient on aripiprazole. Many of the FGAs cause false-positive UDS results and have a less favorable side-effect profile compared to the SGAs; thus, minimizing use of these agents when possible would be suggested Minimizing the use of these agents in high-risk patients when possible may decrease the risk of false-positive results. For patients requiring an SSRI, pharmacists should consider using paroxetine, citalopram, or escitalopram and minimizing the use of fluoxetine and sertraline when appropriate. When using an antidepressant to treat neuropathic pain, minimizing the use of venlafaxine and TCAs and instead using duloxetine should be considered. Gabapentin and pregabalin have a minimal risk of causing false-positives and are other options that could be used. Trazodone is an antidepressant frequently used as a sleep aid. Minimizing its use and instead using mirtazapine or sedative-hypnotics when appropriate would be another consideration Furthermore, false-negatives may also occur because the UDS is simply unable to detect the agent. For example, UDS tests for

6 benzodiazepines commonly result in false-negatives for agents that have poor crossreactivity with the assay. 7 Most assays for benzodiazepines detect their presence in the urine by testing for nordiazepam and oxazepam, the main metabolites of most benzodiazepines. 2 Agents that follow a different metabolic pathway, such as triazolam, alprazolam, clonazepam, and lorazepam, have poor cross-reactivity with the assay due to the absence of these metabolites and thus frequently produce false-negative results. 2,7 Therefore, to decrease the need for confirmatory testing, diazepam, oxazepam, and temazepam may be preferred. Urine drug screening is a common way to test for compliance with medications having high abuse potential. False-negatives and falsepositives from immunoassays can lead to adverse consequences for patients and providers. By identifying medications that contribute to false-negatives and false-positives, pharmacists decrease misinterpretations from urine drug screens. Unexpected results from urine immunoassays should have a confirmatory gas chromatography mass spectrometry or a high-performance liquid chromatography test performed. Pharmacists can provide guidance in selecting appropriate drug therapies that are less likely to cause false readings, thus decreasing the need for additional testing. False-positive methadone levels have been documented with diphenhydramine 100 to 200 mg 2-4,14 and doxylamine intoxication. 4,15 Additionally, doxylamine intoxication has produced false-positive opiate 14 and PCP 2 levels, and brompheniramine use may cause false-positive amphetamine 4 and LSD 3,9 levels. Consider using second-g In addition to false-negatives, pharmacists need to consider the potential for false-positive UDS results and be aware of medications that may cause false-positives. TABLE 2 summarizes many medications that have been reported to cause false-positive results with common substances of abuse or tricyclic antidepressants (TCAs). 1-4 False-positives can occur when a medication has a crossreactivity with the immunoassay, often due to a similarity in the structure of the parent medication or one of its metabolites to the tested drug. 2 The occurrence of false-positives is mostly affected by the type of immunoassay used and by the particular agent being tested. 2. Urine Drug Screening: Minimizing False-Positives and False-Negatives to Optimize Patient Care. Assistant Professor of Pharmacy Practice South Dakota State University. To aid in interpreting UDS results, pharmacists should acquire a thorough list of all the patient's prescription, OTC, and herbal medications prior to testing, as well as discuss adherence to medications. When a negative screening result is obtained, pharmacists should carefully consider the potential for a false-negative result, especially for patients receiving UDS testing to assess compliance with a medication regimen or for those exhibiting behaviors or risk factors suggestive of drug abuse or drug dependency. 1. When selecting therapeutic agents for high-risk patients, pharmacists should consider minimizing the use of drugs known to cause false-positive results, if possible. The selection of an appropriate therapeutic agent for a patient depends on numerous factors, such as the effectiveness and adverse-effect profile of the drug; therefore, minimizing the use of medications shown to cause false-positives must be weighed against clinical judgment in product selection. However, for patients undergoing frequent UDS testing, selecting an agent least likely to cause false-positives would be an important consideration to help minimize adverse consequences to patients from potentially misinterpreted results. This application requires Javascript. Please turn on Javascript in order to use. Clinical Pharmacist, Center for Family Medicine Adjunct Assistant Professor of Family Medicine. In addition to the antiemetics promethazine and doxylamine, metoclopramide and prochlorperazine have had documented false-positive LSD results. 3 Consider minimizing the use of these agents and selecting 5-HT 3 receptor antagonists such as ondansetron to

7 decrease false readings in high-risk populations. 3.