Study Reports a 12.3% Rate of Bladder Cancer Mortality at 10 Years for Patients With High-Risk Bladder Cancer

Age-standardised death rates from Malignant neoplasms by country (per 100,000 inhabitants). (Photo credit: Wikipedia)

Cancer 2013 Jun 04;[EPub Ahead of Print], K Chamie, MS Litwin, JC Bassett, TJ Daskivich, J Lai, JM Hanley, BR Konety, CS Saigal

TAKE-HOME MESSAGE

An examination of outcome for over 7000 patients with high-grade non-muscle invasive bladder cancer reports a 12.3% rate of bladder cancer mortality at 10 years.

---

ABSTRACT
Background: Patients with bladder cancer are apt to develop multiple recurrences that require intervention. The recurrence, progression, and bladder cancer-related mortality rates were examined in a cohort of individuals with high-grade non-muscle-invasive bladder cancer.
Methods: Using linked Surveillance, Epidemiology, and End Results (SEER)-Medicare data, subjects were identified who had a diagnosis of high-grade, non-muscle-invasive disease in 1992 to 2002 and who were followed until 2007. Multivariate competing-risks regression analyses were then used to examine recurrence, progression, and bladder cancer-related mortality rates.
Results: Of 7410 subjects, 2897 (39.1%) experienced a recurrence without progression, 2449 (33.0%) experienced disease progression, of whom 981 succumbed to bladder cancer. Using competing-risks regression analysis, the 10-year recurrence, progression, and bladder cancer-related mortality rates were found to be 74.3%, 33.3%, and 12.3%, respectively. Stage T1 was the only variable associated with a higher rate of recurrence. Women, black race, undifferentiated grade, and stage Tis and T1 were associated with a higher risk of progression and mortality. Advanced age (≥ 70) was associated with a higher risk of bladder cancer-related mortality.
Conclusions: Nearly three-fourths of patients diagnosed with high-risk bladder cancer will recur, progress, or die within 10 years of their diagnosis. Even though most patients do not die of bladder cancer, the vast majority endures the morbidity of recurrence and progression of their cancer. Increasing efforts should be made to offer patients intravesical therapy with the goal of minimizing the incidence of recurrences. Furthermore, the high recurrence rate seen during the first 2 years of diagnosis warrants an intense surveillance schedule.

---

Cancer

Recurrence of High-Risk Bladder Cancer: A Population-Based Analysis

Cancer 2013 Jun 04;[EPub Ahead of Print], K Chamie, MS Litwin, JC Bassett, TJ Daskivich, J Lai, JM Hanley, BR Konety, CS Saigal

Related articles

• Bladder cancer recurrence and mortality could decline with better treatment compliance
• Treatment Compliance Could Lower Bladder Cancer Recurrence and Death Rates
• Patients, experts shed light on bladder cancer in Canada
• Study Finds Bladder Cancer Recurrence And Mortality Could Improve With Better Treatment Compliance
• Bladder Cancer Causes and Symptoms in Women
• Study: Frequent marijuana use tied to reduced bladder cancer risk
• Bladder Cancer Recurrence Could Improve With Better Treatment Compliance
• Bladder cancer recurrence and mortality could decline with better treatment compliance
• New Test For Bladder Cancer Will Significantly Improve Quality Of Patient Care

Medical Errors of Diagnosis Harm More Than Treatment Mistakes

Via: Healthy Skepticism (Facebook Page)

Source: ourhealthcaresucks

CGI image of rod piercing Phineas Gage's skull taken from NINDS public domain page at http://www.ninds.nih.gov/health_and_medical/pubs/tbi.htm (Photo credit: Wikipedia)

Another report on medical errors in America’s healthcare system cautions that these early-stage medical errors account for more medical harm – both preventable deaths and disability – than treatment errors.

In this study, Johns Hopkins researchers reviewed 25 years of medical errors – reflected in medical malpractice payouts – and found that diagnostic errors accounted for more payouts than surgical mistakes or medication overdoses.

Medical errors of improper diagnoses – missed, delayed and wrong diagnoses – accounted for the single largest proportion of such payouts at over a third. And twice as many occurred on an outpatient basis as among hospital inpatients, although the latter were more often lethal (48.4% vs. 36.9%).

The majority were missed diagnoses rather than delayed or wrong diagnoses – and the numbers are vastly understated because they only include those that led to malpractice claims. Most medical errors never reach the point of a malpractice claim.

15-40% Misdiagnoses?

Medical errors is a subject I address in-depth in Our Healthcare Sucks, including the following excerpts:

An estimated 15% of medical diagnoses are in error, with autopsy results showing diagnostic error rates in select areas up to 40%.[1]…

According to an article in The New England Journal of Medicine: [2]

 “125 million (Americans live) with chronic illness, disability, or functional limitation….

“The typical Medicare beneficiary saw two primary care physicians and five specialists (a) year…

“Patients with several chronic conditions may visit up to 16 physicians in a year.”

In a mostly seamless delivery system that emphasized and rewarded coordination of care and avoidance of redundant tests and procedures, maybe it would be possible to maintain quality despite such fragmentation of care.

But the U.S. medical delivery system is anything but “seamless” and, even if it were, it would still require a level of professional precision that’s sorely missing. Physician diagnostic error rates have been estimated as low as 5% (still 1 in 20) and as high as 40% based on autopsy results, with 15% the likely average ballpark.

That’s a huge margin of error that underscores the need to take what your doctor tells you with a grain of salt, at least until you’re able to get it confirmed by another opinion or by imaging or lab test results.

A special Supplement in The American Journal of Medicine [3] addressed this issue with a comprehensive review of the medical literature “Concerning teaching, learning, reasoning and decision making as they relate to diagnostic error and overconfidence”.[4]

According to the authors of this review:

“Being confident even when in error is an inherent human trait, and physicians are no exception. When directly questioned, many clinicians find it inconceivable that their own error rate could be as high as the literature demonstrates…

“This reflects both overconfidence and complacency (emphasis added).”

An article on this report makes this dismal observation:

“Medical practitioners really do not use systems designed to aid their diagnostic decision making…physicians have underutilized decision-support systems and misdiagnosis rates remain high.”

Say It Ain’t So, Doc

Many patients don’t want to believe their doctors are capable of such high rates of medical misdiagnoses – any more than they want to believe our higher rates of medical errors than other developed countries. These are very intelligent, well-educated people, after all – generally more so than the patients they treat. How can such smart people make so many diagnostic errors?

The obvious answer lay in our fee-for-service payment system that penalizes doctors for spending the time required for thoughtful assessments and diagnoses. These “cognitive” services are reimbursed at far lower levels than procedures – whether needed or not.

Medicare and other payers are partly to blame for perpetuating this skewed payment system, as are those in the medical profession who choose to maximize their incomes at their patients’ expense. No one’s forcing them to submit to these skewed incentives, after all. Some don’t, so it’s not impossible – but they’re generally considered either saints or fools by their peers.

Anchoring On First Impressions

But there’s more to our excess medical errors than that. Dr. Jerome Groopman helps us understand how doctors’ training perpetuates mental shortcuts and crutches that contribute greatly to medical errors – and to diagnostic errors specifically. Here’s another excerpt from Our Healthcare Sucks on the subject:

Enter Dr. Jerome Groopman and his New York Times best seller, How Doctors Think, in which he lays out many of the sources of medical error, misdiagnosis, and misjudgment.

He helps us understand how such smart people can make so many mistakes by explaining that it’s not a function of intellect.

Instead, it’s a type of cognitive dysfunction in which many physicians – who are trained and required by their business mandates to make snap judgments – can fall prey to all sorts of errors in thinking.

Here are a few sentences from Dr. Groopman’s book that bear on this discussion:

“Misdiagnosis is different (from medical errors)…experts studying misguided care have concluded the majority of errors are due to flaws in physician thinking, not technical mistakes…

“In one study of misdiagnoses…some 80% could be accounted for by a cascade of cognitive errors…ignoring information that contradicted a fixed notion….

“As many as 15% of all diagnoses are inaccurate…

“Physicians tend to go with their first impression…

“The cognitive mistakes that account for most misdiagnoses…largely reside below the level of conscious thinking (emphasis added).”[5]

Doctors, he explains, tend to get stuck on first impressions, something he calls “anchoring” because it anchors or fixates their diagnosis and often that of other doctors to whom you might be referred.

Or they just might not like certain patients, leading them to cut them off from fully describing their symptoms and settle for the most convenient or available treatment.

If they think the patient is a complainer or hypochondriac, they may assume a benign condition and minimize the likelihood of serious disease.

Now these cognitive flaws, as Dr. Groopman describes them, are all understandable as human failings – and Groopman quite understands them having labored with them himself – but are they professional?

Don’t patients have a right to expect more of their highly-paid doctors?

Why should patients have to worry about whether their doctor likes them or not and fear, quite correctly it seems, that it will bias their treatment?

This isn’t high school, after all.

Defensive Medicine is A Failed Response 

The medical profession has failed to address this crisis in patient safety with the urgency it deserves – opting instead for defensive medicine practices intended to insulate them from malpractice liability rather than address medical errors head-on.

This defensive mindset prevents the profession from engaging more meaningfully to correct both diagnostic and treatment failures.

And with more patients seeking medical care as Obamacare is implemented, doctors will have even less time to spend with patients. The risk of diagnostic errors – and medical errors generally – is likely to increase as a result.

A thorough diagnostic work-up takes time and thought – both of which are in increasingly short supply in America’s broken healthcare system.

All of which means patients will have to learn how to protect themselves and their loved ones when engaging with our fundamentally flawed medical system.

[1] The Autopsy as an Outcome and Performance Measure. Agency for Healthcare Research and Quality. Evidence Report/Technology Assessment. Number 58. Oct. 2002.

[2] Coordinating Care – A Perilous Journey through the Health Care System, The New England Journal of Medicine, Vol. 358:1064-1071, 3/6/08.

[3] The American Journal of Medicine, Volume 121, Issue 5A, May, 2008.

[4] Elsevier Health Sciences (2008, April 29). Will You Be Misdiagnosed? How Diagnostic Errors Happen. ScienceDaily.
[5] How Doctors Think. Dr. Jerome Groopman, Houghton Miflin Company.2007.

Related articles

• Deadly medical errors: A hidden health care issue
• Diagnostic errors more common, costly and harmful than treatment mistakes
• NCH earns another 'A' in Leapfrog Group patient safety score
• Peer Review Professionals Learn How to Manage Risk in the Emergency Department Through Effective Peer Review
• Where are we in our Campaign?
• Diagnostic errors more common, costly and harmful than treatment mistakes
• Lessons About Medical Error Learned Watching I Love Lucy.
• The Darkest Year of Medical School
• Diagnostic Errors Cause Up To 160,000 Deaths Annually, USA

Why Patients Don’t Report Medical Errors

Are we talking only about Medicare in USA ? Seems to be genocide.

iStockphoto

by Marshall Allen
ProPublica, Sept. 25, 2012,

 

 

I was recently browsing through the nearly 200 stories we’ve compiled with our Patient Harm Questionnaire, when I was reminded again of a troubling truth. Many of the people who suffer harm while undergoing medical care do not file formal complaints with regulators. The reasons are numerous: They’re often traumatized, disabled, unaware they’ve been a victim of a medical error or  don’t understand the bureaucracy.

That’s a problem for those individual patients and for the rest of us. There are many places to complain: a state licensing agency; a professional licensing board that monitors doctors or nurses; the Joint Commission, which accredits hospitals or a Medicare Quality Improvement Organization. But if there are no complaints, there are no independent investigations, and that means no outside accountability for providers who may have made mistakes, and no public inspection reports that documents the case -- assuming an agency makes reports public, which is not always the case. It’s a collective problem because patient safety flaws that remain hidden, if they are not corrected, may be repeated.

We have staggering estimates of the number of people harmed while undergoing medical treatment. A review of medical records by the U.S. Health and Human Services Department’s inspector general found that in a single month one in seven Medicare patients was harmed in the hospital, or roughly 134,000 people. “An estimated 1.5 percent of Medicare beneficiaries experienced an event that contributed to their deaths,” the IG found, “which projects to 15,000 patients in a single month.”

But there’s no central system in place to tally and track these events. There’s no way to know when and where patients are being harmed or to tell if the problem is worse in one place than another.

It’s not like keeping track of patient harm is a new idea. More than a decade ago the Institute of Medicine’s landmark “To Err Is Human” report called for a national system to capture cases of serious harm to patients or death. The report said accurate reporting provides accountability and knowledge that leads to learning. That’s information that could save lives.

“You really can’t improve what you don’t measure,” said Dr. Julia Hallisy, president of the Empowered Patient Coalition. “How do you know where to focus your improvement efforts if you haven’t measured what’s happening in the first place?”

Efforts at the state level appear to be falling short, according to federal inspectors. In many states, hospital are required by law to file a report every time a patient suffers unexpected harm -- often called  “sentinel” or “adverse” events. But a July report by the HHS inspector general’s office found that only 12 percent of harmful events identified by the office even met state requirements for reporting them. Compounding the problem: Hospitals themselves only reported 1 percent of the harmful events.

We found something similar when I was a reporter in Las Vegas. We used hospital billing records to identify 3,689 cases of patient harm at the city’s hospitals in a two-year period. Each of those cases would fit the state’s definition of a “sentinel event,” meaning the hospitals were required by law to report them. Yet in the same time period they reported to the state only 402 sentinel events.

The federal Agency for Healthcare Research and Quality is now accepting public comment about a proposed program to encourage consumers to complain about harm suffered while undergoing medical care. The goals include collecting information in a common format, developing prototype methods for gathering information on the phone and Internet and creating a follow-up questionnaire for medical providers. Patients will be asked what happened, who was involved and for permission to follow up with the providers involved in the event.

I recently referred the 1,000 members of the ProPublica Patient Harm Facebook Group to a story about the proposal in The New York Times. Many members of the group have suffered harm firsthand and filed complaints, so the article created lively discussion:

• Robin Karr said that based on her experience, she’s skeptical about reporting harm directly to the government “but not without hope” about the proposed program.
• Debra Van Putten said she knows many people who have filed complaints about harm they suffered, but little came of their efforts. Patients want more than mere acknowledgement, she said. They want accountability for whoever is responsible.
• Martha Deed said there are so many barriers to a patient reporting harm -- emotional trauma and physical disabilities, feeling intimidated by providers, social pressure not to complain -- that a passive questionnaire is unlikely to elicit responses. Instead, the patient harm information should be gathered in a way that’s standardized, she said, like the national survey that’s administered to recently discharged hospital patients that has results publicly reported on Hospital Compare.

That’s food for thought for those developing the program. Official public comment is due Nov. 9 and can be sent to Doris Lefkowitz, the AHRQ reports clearance officer: doris.lefkowitz@AHRQ.hhs.gov.

We’d also love to hear your comments. How do those of you who work in the medical field feel about this type of reporting system? Patients, what do you think about it? And what would you recommend as characteristics that would be essential to such a program?

Related articles

• Medical Errors Start With Misdiagnoses
• When Harm in the Hospital Follows You Home
• When Harm in the Hospital Follows You Home
• How Hospitals Can Kill Us
• National Patient Safety Foundation to Host Webcast on Patient Safety Across the Continuum of Care
• Telehealth can relieve pressure on the NHS - while improving patient care
• 10 Medical Errors that Can Kill You in the Hospital
• U.S. fraud alert warns of doctors' ties to medical devices
• Catalogue of harm to NHS patients is revealed
• Discussion: How to Improve Accountability in Medicine?

JAMA. 2013 Apr 17;309(15):1599-606. doi: 10.1001/jama.2013.2773.

Relationship between occurrence of surgical complications and hospital finances.

Eappen S, Lane BH, Rosenberg B, Lipsitz SA, Sadoff D, Matheson D, Berry WR, Lester M, Gawande AA.

Source

Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts, USA.

Abstract

IMPORTANCE:

The effect of surgical complications on hospital finances is unclear.

OBJECTIVE:

To determine the relationship between major surgical complications and per-encounter hospital costs and revenues by payer type.

DESIGN, SETTING, AND PARTICIPANTS:

Retrospective analysis of administrative data for all inpatient surgical discharges during 2010 from a nonprofit 12-hospital system in the southern United States. Discharges were categorized by principal procedure and occurrence of 1 or more postsurgical complications, using International Classification of Diseases, Ninth Revision, diagnosis and procedure codes. Nine common surgical procedures and 10 major complications across 4 payer types were analyzed. Hospital costs and revenue at discharge were obtained from hospital accounting systems and classified by payer type. MAIN OUTCOMES AND MEASURES: Hospital costs, revenues, and contribution margin (defined as revenue minus variable expenses) were compared for patients with and without surgical complications according to payer type.

RESULTS:

Of 34,256 surgical discharges, 1820 patients (5.3%; 95% CI, 4.4%-6.4%) experienced 1 or more postsurgical complications. Compared with absence of complications, complications were associated with a $39,017 (95% CI, $20,069-$50,394; P < .001) higher contribution margin per patient with private insurance ($55,953 vs $16,936) and a $1749 (95% CI, $976-$3287; P < .001) higher contribution margin per patient with Medicare ($3629 vs $1880). For this hospital system in which private insurers covered 40% of patients (13,544), Medicare covered 45% (15,406), Medicaid covered 4% (1336), and self-payment covered 6% (2202), occurrence of complications was associated with an $8084 (95% CI, $4903-$9740; P < .001) higher contribution margin per patient ($15,726 vs $7642) and with a $7435 lower per-patient total margin (95% CI, $5103-$10,507; P < .001) ($1013 vs -$6422).

CONCLUSIONS AND RELEVANCE:

In this hospital system, the occurrence of postsurgical complications was associated with a higher per-encounter hospital contribution margin for patients covered by Medicare and private insurance but a lower one for patients covered by Medicaid and who self-paid. Depending on payer mix, many hospitals have the potential for adverse near-term financial consequences for decreasing postsurgical complications.

Comment in

The following popper user interface control may not be accessible. Tab to the next button to revert the control to an accessible version.

Destroy user interface controlMaking surgical complications pay. [JAMA. 2013]

Related articles

• Reducing surgical complications may increase costs
• Study Examines Relationship Between Occurrence Of Surgical Complications And Hospital Finances
• Study examines relationship between occurrence of surgical complications and hospital finances
• Post-Surgical Complications Contribute To Hospital Revenue
• Post-Surgical Complications Contribute T
• Improving Quality Patient Outcomes a Money Loser for Hospitals
• Hospitals Profit $40,000 for Some Patients With Complications
• Patients With Surgical Complications Provide Greater Hospital Profit-margins: Research

When it Comes to Colonoscopies, Recession and Co-Pays Matter

Image via Wikipedia

Source: http://blogs.wsj.com/health/
By Katherine Hobson By a number of indicators, people have been using fewer medical services during the economic downturn. Screening colonoscopies apparently aren’t immune to that trend, according to a study appearing in the March issue of Clinical Gastroenterology and Hepatology. The study finds that during the recent recession, commercially insured Americans had fewer of the tests to screen for cancer — a test that saves lives, according to research published just this week. According to the analysis, there were about 500,000 fewer screening colonoscopies among commercially-insured people aged 50 to 64 than you’d expect during the most recent recession, which officially lasted from December 2007 to June 2009. (The study used the National Bureau of Economic Research’s official designation for the recession.) The U.S. Preventive Services Task Force recommends colorectal cancer screening using several methods, including colonoscopy, for adults aged 50 to 75. The analysis didn’t find that people forgoing colonoscopy were instead using other, cheaper methods, such as fecal occult blood tests or sigmoidoscopy. Researchers looked at the rates of screening before and after the recession, then applied their findings to population data to come up with an estimate of 516,309 colonoscopies that would have occurred absent the downturn. Data came from 106 health plans and added up to a nationally representative picture of the commercially insured population, the authors say. It doesn’t include people who didn’t have a screening colonoscopy because they lost insurance coverage during the recession, says Spencer Dorn, an author of the study and an assistant professor of medicine in the division of gastroenterology at the University of North Carolina at Chapel Hill. And it doesn’t include Medicare or Medicaid beneficiaries. The analysis also found that when it comes to colonoscopy, cost sharing appears to be a deterrent. No matter the economic climate, people with higher out-of-pocket costs — $300 or more for the procedure — were less likely to be screened than those with lower costs, defined as $50 or less. That gap “widened during the recession,” says Dorn. Under the health-care overhaul law, colonoscopy — and other preventive services — must be covered with no cost sharing by Medicare, Medicaid and new private-insurance plans. (“Grandfathered” plans that haven’t significantly changed their design are exempt.) The drop in utilization seen in the study “could have negative consequences down the line,” says Dorn, in terms of cancers being caught at a later stage. (The screening study out this week suggests it might also lead to deaths from the disease.) The CDC last year reported an increase in screening rates for colorectal cancer from 2002 to 2010, but that estimate included all 50- to 75-year-olds and didn’t break down what happened during the intervening years.

Related articles

• When it Comes to Colonoscopies, Recession and Co-Pays Matter (blogs.wsj.com)
• Among People With Health Insurance, The Recession And High Co-Pays Tied To Fewer Colonoscopy Screenings (medicalnewstoday.com)
• Recession and high co-pays tied to fewer colonoscopy screenings among people with health insurance (medicalxpress.com)
• Recession and high co-pays tied to fewer colonoscopy screenings among people with health insurance (eurekalert.org)
• Many Cancer Deaths Prevented by Colonoscopy (webmd.com)
• CT Colonography Shown to be Comparable to Standard Colonoscopy for People Ages 65 and Over (multivu.com)
• Study Supports CT-Based 'Virtual' Colonoscopy to Spot Colon Cancer (news.health.com)
• Colon Cancer Alliance and American College of Radiology demand Medicare cover virtual colonoscopy (eurekalert.org)
• Fewer Americans Received Life-Saving Cancer Screenings During Recession (thinkprogress.org)
• Colorectal cancer death risk cut in half through colonoscopies, study shows - CBS News (cbsnews.com)

Independent Events

                       Image via WikipediaIndependent Events

I was speaking with a patient recently who was explaining why he thought that colon cancer screening with fecal occult blood testing (FOBT) was equivalent to colonoscopy. He wished to avoid colonoscopy for all the usual reasons, but also believed logically that it was not a superior test.

I won't get into the actual evidence behind the two methods of screening; that is not an issue for this post. Instead, I want to discuss his argument. He assumed that colonoscopy had a sensitivity (probability of the test being positive in someone with a significant colon lesion) of 98%, and this figure is in the ballpark of believable numbers. Let's assume that the sensitivity of FOBT is around 35% (also a reasonable ballpark figure). At that rate, he said, since colonoscopy is performed once every 10 years, and FOBT is performed yearly, after 10 years the performance of the two tests is similar with FOBT having a cumulative sensitivity of 99%.

There are two important problems with this argument. The first, which I will just mention in passing, is also the more obvious. If a test has to be repeated for 10 years to detect a cancer, that cancer may grow and become incurable during the testing period. Had it been found at year 1, it might have had a better chance of being cured.

The second problem is the focus of this post, and to examine it, we need to understand the calculation the patient was performing to get to a cumulative sensitivity of 99%. This is the same type of calculation that is often presented when thinking about the probability of an abnormal lab test due to chance alone in a battery of lab tests. The argument goes as follows:

We define "normal" in a lab test that has a continuous result (like serum sodium) as the range of values that captures 95% of healthy patients.
That means that 5% of healthy patients (or 1 in 20) will have an "abnormal" result on the test.
If we run a battery of different tests on a patient, each of which has a similarly defined normal range, the probability of a single abnormal result due to "chance" goes up.

The actual calculation of the likelihood of an abnormal test result typically confuses medical students and early residents until they've heard it presented repeatedly. A common assumption is that if there is a 1 in 20 chance of an abnormal result on each test, then if 20 tests are run there will definitely be an abnormal result. This is not the correct calculation. Under the usual assumptions that people make in thinking about this, the calculation would be that the probability of all the tests being normal is the probability of a single test being normal raised to the power of the number of tests.

Thus, for 20 tests it would be 0.95^20, which is 0.36. The probability that at least one such test will be abnormal due to "chance" is 1-0.36 or 0.64. Or, about 2/3 of normal patients would be expected to have at least one abnormal test on a battery of 20 tests under these assumptions.

So the patient utilizing FOBT for colon cancer screening was saying that, with a sensitivity of about 35%, he could expect a false negative rate of 0.65 per test but that 0.65^10 (for the ten years of testing) yielded a miss rate of 1%. This cumulative sensitivity would then be similar to that of a single colonoscopy, so why should he get the invasive procedure?

And so we come to the second problem with the patient's argument: each round of testing is not an independent event.

The calculations I described above for cumulative probabilities make the assumption that the individual events are independent from each other. That is, the result of one test has no influence on the others.

If you flip a fair penny three times and get three heads, there is still a 1 in 2 chance that it will come up heads on the fourth flip. But if you perform FOBT once for colon cancer and it is negative it might be in the setting of your particular precancerous lesion that doesn't tend to bleed. If so, it's less likely to be bleeding on subsequent FOBT than an "average" lesion and so the cumulative sensitivity cannot assume independence of events. This is not just a theoretical issue: based on some research, repeated testing is thought to actually have a cumulative sensitivity of around 85%, not 99%.

So the patient was miscalculating in his decision about how to be screened for colon cancer. I actually briefly discussed this with him during the appointment, but since the real issue was that he did not want a colonoscopy he was singularly uninfluenced by the math.

This plays out in other areas as well, though:

What about that standard example above regarding batteries of lab tests that all medical students and residents are taught? The tests in the battery, too, are clearly not independent events. Normal and abnormal tests tend to cluster and so it is likely that the probability of the 20th test being abnormal in a healthy patient is affected by whether the prior 19 tests included any abnormal results.

To contrast with the assumption of probabilities in the face of independent events, here we are talking about "conditional" probabilities where we want to know the likelihood of an event given some other set of events. However, in the real world we have very few data about these situations. If, for instance, I wanted to know how likely, due to random variation, a patient with an abnormal serum sodium and chloride is to have a high serum potassium, it is extremely unlikely that I could get a high quality answer without doing my own primary research.

This problem of not knowing conditional probabilities when faced with non-independent events has an important effect on how diagnostic strategies might be misinterpreted if clinicians really started utilizing a test parameter that is a favorite in the EBM community but has not really permeated the clinical world. I'll address this in a future post.

Related articles

• Blood test for colon cancer screening beneficial for some seniors, but not for many others (eurekalert.org)
• Proper Bowel Prep Key to Effective Colon Cancer Screening (nlm.nih.gov)
• Colorectal Screenings can be Lifesavers (cancerhelpandtreatment.wordpress.com)
• Colonoscopy screenings may occur more often than recommended; benefit uncertain in some older adults (eurekalert.org)
• Proper Health Screening Chart (checkupyourcheckup.wordpress.com)
• Screening Colonoscopies Done More Often Than Recommended On Medicare Beneficiaries (medicalnewstoday.com)
• Canadians too ‘squeamish’ about testing for colorectal cancers (theglobeandmail.com)
• Colorectal cancer screening rates on rise among Medicare beneficiaries due to expansion of coverage (scienceblog.com)
• Colorectal cancer cases on the rise: Report (calgaryherald.com)
• Colorectal cancer screening rates on rise among Medicare beneficiaries due to expansion of coverage (eurekalert.org)