What Are the Odds of Failing a Drug Test?

By Roger Chriss, Columnist

What are the odds that a person who tests positive for an illicit drug is actually using that drug?

That is a vital question in pain management and the opioid crisis, because millions of pain patients undergo drug tests regularly and some are falsely accused of failing them. The answer is not just a matter of looking at the accuracy of the test.

In a simple situation, like a toss of a coin or a roll of a die, computing the probability of an outcome is elementary. Most people realize that a toss of a coin has an equal chance of coming up heads or tails.

But drug testing is not as simple. It is an example of conditional probability. A drug test that is 95% accurate will not find drug users 95% of the time. That is because the test is applied to both drug users and non-users. We have to use a calculation known as Bayes’ Theorem to determine the real probabilities.

Bayes’ Theorem calculates the probability of one event happening given that another event has already happened. In terms of drug testing, this means the probability that a randomly selected person who has a positive test did in fact use that drug.

To perform the calculations, we need to know two things:

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  1. The accuracy of the drug test
  2. The “base rate” at which drug use occurs in the population at large.

The accuracy of drug tests varies widely. A 2010 study estimated that drug tests generally produce false-positive results in 5% to 10% of cases and false negatives in 10% to 15% of cases.

Data on the base rate of drug use also varies. The CDC claims as many as 25% of chronic pain patients develop signs of opioid use disorder. However, a Cochrane review found addiction in less than 2% of long-term opioid users.

This gives us four general scenarios to consider when estimating the probability that a chronic pain patient with a positive test result is actually misusing opioids:

Scenario I (25% base rate; 95% accurate drug test):  90%
Scenario II (25% base rate; 90% accurate drug test): 83%
Scenario III (2% base rate; 95% accurate drug test):  29%
Scenario IV (2% base rate; 90% accurate drug test):  17%

With a high base rate of opioid misuse and a more accurate test, the probability is high at 90 percent. On the other hand, as the base rate falls and test accuracy decreases, the probability drops significantly, down to 17 percent. This means that the probability of a person getting a false positive result increases.

The Base Rate Fallacy

Bayes’ Theorem clearly shows that the base rate of drug use has a large effect on the probability that a person will get a false test result. Because clinical decisions and healthcare policy are often based on the results of such tests, knowing the probabilities is vitally important.

The base rate fallacy occurs when a decision is made without taking the real base rate into consideration. As shown above, the upper value of 25% is more than 10 times the lower value of 2 percent, indicating a high degree of uncertainty in the base rate.

Moreover, the base rate is not the same in all locations or across all populations. Drug abuse is known to be higher in some places and among some age groups. The accuracy of drug tests also represents an average, but factors such as biochemical individuality and testing conditions may influence actual performance.

Further, drug testing is not an entirely random process. For instance, prior to prescribing opioid medication, a doctor may perform a risk assessment using an Opioid Risk Tool. A doctor may also have hints that a patient is abusing opioids to motivate testing. In either case, randomness is lost and the base rate shifts.

Conditional probability produces counter-intuitive results, with a high degree of dependence on the base rate -- itself a number that requires constant attention.

The bottom line is that drug testing alone is not foolproof. Clinical judgment by experienced physicians, combined with information such as pharmacy data, pill counts and medical records, will always get better odds than drug testing alone.

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Roger Chriss lives with Ehlers Danlos syndrome and is a proud member of the Ehlers-Danlos Society.

Roger is a technical consultant in Washington state, where he specializes in mathematics and research.

The information in this column should not be considered as professional medical advice, diagnosis or treatment. It is for informational purposes only and represents the author’s opinions alone. It does not inherently express or reflect the views, opinions and/or positions of Pain News Network.

Do Half of Americans Really ‘Misuse’ Drugs?

By Pat Anson, Editor

One of the nation’s largest drug testing companies has released a study claiming that over half of Americans who are prescribed medication show signs of drug misuse, including potentially dangerous drug combinations.

In 2016, Quest Diagnostics found that 52% of patient test results were “inconsistent” with their prescribed medications. That was an improvement over the rate found in 2011, when 63% of samples were inconsistent.

The Quest report, titled "Prescription Drug Misuse in America: Diagnostic Insights in the Growing Drug Epidemic," is based on an analysis of 3.4 million laboratory tests performed between 2011 and 2016.

Many of the specimen samples came from patients being treated in pain management and addiction treatment clinics, which are not representative of the population as a whole.

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Like previous studies of its kind, Quest broadly defines what constitutes drug “misuse” – a misleading term many people associate with abuse, addiction and diversion. Nearly a quarter of the patients (23%) with inconsistent results had no drugs detected in their system, which simply means they were not taking medications as directed.

The other 77% tested positive for illegal drugs or for a medication they were not prescribed.

"Over the past several years, federal and state government, clinician organizations, public health advocates and providers have all launched campaigns to educate the public about the perils of prescription drug misuse, which hypothetically should have yielded a significant rate of improvement. Yet our study shows that every other American tested for possible inappropriate use of opioids and other prescription drugs is potentially at risk," said F. Leland McClure, PhD, director of medical affairs at Quest Diagnostics.

"This finding is rather shocking, and speaks to the challenges of combating the nation's drug misuse epidemic."

Are the results really all that shocking? Or were they ginned up to hype the so-called epidemic? Consider some of the reasons a patient may not take a drug or have an inconsistent test result:

  • Patient didn't like side effects from a medication
  • Pain or other symptoms have subsided, so medication is not needed
  • Patient skipped a dose
  • Patient cannot afford a medication
  • Patient can’t find a pharmacy willing to fill their prescription
  • Patient may be a “rapid metabolizer” of a medication
  • Physician may not be aware another doctor prescribed a drug
  • Inaccurate drug test

The latter is a very real problem in the drug testing industry. As PNN has reported, “point-of-care” urine tests widely used by pain management and addiction treatment doctors to screen patients for illicit drug use are wrong about half the time, often giving false positive or false negative results for drugs like marijuana, oxycodone and methadone. 

The Quest study identified some disturbing and encouraging trends in drug use.

It wasn't opioids but benzodiazepines – a class of anti-anxiety medication that includes Xanax – that were most likely to be misused by adults over the age of 25.  Marijuana was most likely to be misused by people aged 18 to 24.   Opioids were second in both age groups.

Quest researchers found a striking decline in drug misuse among adolescents 10 to 17 years of age. The inconsistency rate for adolescents dropped from a whopping 70% in 2011 to 29% in 2016. Amphetamines and attention deficit disorder drugs were most likely to be abused by adolescents.

Among nearly 34,000 patient samples tested for opioids, alcohol and benzodiazepines, more than 20% were positive for opioids and benzodiazepines, 10% were positive for alcohol and opioids, and 3% were positive for all three.  Any combination of these drugs raises the risk of respiratory depression and overdose.

Misuse rates were higher for men and women of reproductive age (58%) than in the general study population (52%). The findings are significant because opioid and benzodiazepine use may decrease male fertility and, if taken during pregnancy, increase the risk of birth defects and other health concerns.

Quest is one of several drug testing laboratories that have been fined millions of dollars for paying kickbacks to physicians and patients for medically unnecessary tests.  Recent guidelines adopted by the American Society of Addiction Medicine warn doctors about ordering expensive drug tests that have led to “unethical and/or fraudulent activities.”

Feds Say Bankrupt Drug Lab Paid Millions in Kickbacks

By Pat Anson, Editor

A bankrupt drug testing lab with a checkered history has been linked to a large money laundering and pill mill operation in Tennessee.

According to an updated indictment in U.S. District Court in Knoxville, Confirmatrix Laboratory in Georgia and Sterling Laboratories in Seattle paid nearly $3 million in illegal kickbacks to have thousands of urine drug test samples sent to them from patients at the Knoxville Hope Clinic (KHC). In return, the labs submitted false claims for "unnecessary" drug tests to Medicare and TennCare, Tennesee’s Medicaid program.

“Confirmatrix, by and through its principals and agents, paid bribes and kickbacks to defendants Clyde Christopher Tipton and Maynard Alvarez in return for causing Medicare and TennCare beneficiaries from KHC to be referred to Confirmatrix for medically unnecessary drug screenings,” the indictment alleges.

“Medical providers at KHC prescribed opioids and other controlled substances to thousands of purported pain patients in exchange for grossly excessive fees. The vast majority of the prescriptions were unreasonable and medically unnecessary. Patients were required to keep follow-up appointments every 28 days to continue receiving their prescriptions. Providers at KHC ordered medically unnecessary Drug Screenings for every patient every 28 days.”

Tipton, Alvarez and six other defendants are accused of drug trafficking and money laundering in the long-running investigation of Tennessee pill mills. The ringleader of the pill mill scheme, a 53-year old grandmother named Sylvia Hofstetter, allegedly made millions of dollars while running clinics that prescribed 12 million opioid prescriptions. Prosecutors have alleged that at least nine patients at the clinics died from drug overdoses.

No one affiliated with Confirmatrix or Sterling Laboratories has been indicted so far in the case. Prosecutors say the   alleged kickbacks were paid from August 2013 to July 2016.

As PNN has reported, Confirmatrix filed for Chapter 11 bankruptcy last November, just two days after its headquarters near Atlanta was raided by FBI agents.  The company was founded by Khalid Satary, a convicted felon and Palestinian national that the federal government has been trying to deport for years.

A 2013 study by the Centers for Medicare and Medicaid Services (CMS) listed Confirmatrix as the most expensive drug lab in the country, collecting an average of $2,406 from Medicare for each patient tested, compared to the national average of $751. The bills from Confirmatrix were high because the company ran an average of nearly 120 different drug screens on each patient, far more than any other drug lab.

These and other abusive billing practices finally caused Medicare to lower its reimbursement rates for drug testing, which led to Confirmatrix’s financial problems.

Although it filed for Chapter 11 bankruptcy nine months ago, Confirmatrix remains in business and continues to bill patients and insurance companies for costly drug screens.

Some current and former patients at the Benefis Pain Management Center, a pain clinic in Great Falls, Montana, have received bills from a collection agency seeking well over $1,000 for drug screens that normally cost a few hundred dollars.

“Confirmatrix is out of network, hence I am stuck with the bill unless Benefis writes it off,” one patient told PNN. “I spoke to my insurance about it and they told me that there are labs in Montana that could have done the same thing and would have been covered by my insurance. She asked me, why they would go to a Georgia lab?”

In a statement to PNN in May, a Benefis official defended the clinic’s continued use of Confirmatrix, saying the company performs a valuable service and “waives many costs.”

“The company we have partnered with has an extensive patient assistance program, which is part of the reason they were selected. That company was selected two years ago because it was one of the few labs nationwide that offered quantitative and qualitative testing AND patient assistant programs,” said Kathy Hill, Chief Operating Officer at Benefis Medical Group.

Confirmatrix’s laboratory, office and warehouse space were recently put up for auction by the bankruptcy court under sealed bid.

Study Depicts Half of Americans as Rx Abusers

 By Pat Anson, Editor

Over half of Americans “misused” their prescription drugs last year, according to a new report by a drug testing company that appears to draw several broad and misleading conclusions about the use of opioid pain medication.

Quest Diagnostics analyzed drug testing data from over 3 million patients and found that 54% had some type of prescription drug misuse in 2015 – down from 63% in 2011.

"The key takeaway from this massive, nationally representative analysis is that despite some gains, a large number of patients use prescription drugs inappropriately and even dangerously," said co-researcher Harvey W. Kaufman, MD, senior medical director for Quest Diagnostics.

"The CDC's recent recommendations to physicians to carefully weigh the risks and benefits of opioid drug therapy are a step in the right direction, but clearly more needs to be done to address this public health crisis."

The term “misuse” should be taken with a grain of salt, because it does not mean patients were abusing or addicted to prescription drugs – only that they did not take them as directed.

In 2015, for example, the study found that over half (55%) of the patients who had “inconsistent” test results did not have a prescribed drug in their system – meaning they no longer felt a need to take a medication, didn’t like the drug’s side effects, forgot to take it, or simply couldn’t afford it. It could also mean the drug was ineffective. the wrong drug was prescribed or the doctor made an incorrect diagnosis. There are literally dozens of reasons someone could stop taking a drug.

But patients who had no drugs detected – legal or illegal – were still classified in the “misuse" category.

Nevertheless, while acknowledging there were “methodology limitations” to the study, Quest made some sweeping conclusions about it in a press release, claiming that “the majority of American adults taking opioids and other commonly prescribed medications use them in ways that put their health at risk.”

But according to the study, opioids were not the most commonly misused class of medication. Depending on the age of the patient, that distinction went to amphetamines, benzodiazepines and marijuana. Opiates were the second most likely class of drugs to be misused by adults – but again that includes many patients who did not take opioids that were prescribed or had no drugs at all in their system.

This way of slicing the data has long been used by drug testing companies to make the abuse of opioids appear worse than it is and to justify more testing.

A similar study by Ameritox in 2012 found that nearly a third of older patients did not have a prescribed opioid detected in their urine -- and that was also considered misuse.

“This population has a risk of medication misuse and illicit drug use that warrants attention,” said Harry Leider, MD, who was then Chief Medical Officer of Ameritox. “This data provides a compelling rationale for routinely monitoring medication use in older patients on chronic opioids.”

Ameritox sponsored a study that same year claiming that patients should be drug tested at least four times annually if a doctor believes they are at risk misusing opioids.  The study was approved even though “there currently is a limited evidence base to support the expert panel’s recommendations.”

Guidelines adopted by the CDC earlier this year were also based on weak evidence. They recommend that physicians should use urine drug testing before starting opioid therapy and should re-test patients at least once annually.

As Pain News Network has reported, “point-of-care” urine drug tests that are widely used in doctors’ offices are wrong about half the time – frequently giving false positive or false negative results for drugs like marijuana, oxycodone and methadone.

According to one estimate, drug testing has grown into a lucrative $4 billion dollar a year industry -- “liquid gold” as some have called it – that is projected to reach $6.3 billion by 2019. The competition between drug screening labs is intense and several companies have been fined by the federal government for giving illegal kickbacks to physicians. Last year, Millennium Health agreed to pay $256 million to the federal government to settle fraud and kickback charges. The company later filed for chapter 11 bankruptcy protection.