Trust but Verify: The Impact of Erroneous ACTH Assays

An ACTH assay’s accuracy became so concerning that it warranted a paper in the Journal of the Endocrine Society that detailed five separate cases. Raising awareness of this rare but serious issue can avoid misdiagnoses that put patients in peril. 

This past April, an article appeared in the Journal of the Endocrine Society titled, “Assay-Specific Spurious ACTH Results Lead to Misdiagnosis, Unnecessary Testing, and Surgical Misadventure—A Case Series,” which details five cases of patients whose diagnoses or differential diagnoses of Cushing syndrome were confounded by erroneous results from an adrenocorticotropic hormone (ACTH) assay.

The paper, by Loren Wissner Greene, et al., implicates the Siemens ACTH Immulite Assay – widely used in labs across the country — as the problematic test. “Because many high-volume reference laboratories in the United States use this assay, we believe it is critical to inform physicians, especially endocrinologists and endocrine surgeons, of this ACTH assay problem,” the authors write.

The authors also write that as they were compiling the data on the five patients discussed in this paper, multiple other cases were brought to their attention, leading them to believe these five were not isolated or unique cases. “Since 2012, we have been accumulating a series of cases highlighting serious issues with this assay,” the authors write. “The purpose of the present report was to highlight this problem and provide endocrinologists with the clinical context and suggest a corrective course of action.”

A serious issue indeed: This assay has produced falsely elevated results which led to referral of  these patients for further expensive and invasive diagnostic procedures, including MRI, petrosal sinus sampling and even unnecessary surgery before their results were corrected and clarified by other assays and follow-up.

Specious Results

In late 2015, James W. Findling, MD, a practicing endocrinologist in Menomonee Falls, Wisc., contacted Hershel Raff, PhD about a patient who was referred to Findling with plasma ACTH results done on the Siemens Immulite instrument that did not agree with the results Findling got from his hospital’s laboratory that used the Roche Cobas ACTH assay. At that time, Raff’s laboratory was using the Tosoh AIA assay, so Findling wanted to see what results the AIA would produce. The Roche and the Tosoh methods showed results consistent with the patient’s clinical presentation and other laboratory results.

Around this time, Greene, FACP, FACE, MD, MA, of the New York University School of Medicine, had a similar case, so Raff advised Greene to assay her patient’s samples on an alternate instrument, and the ACTH results from the alternate assay lined up with the clinical picture. Almost simultaneously, Findling heard from Eliza B. Geer, MD, a practicing endocrinologist at Memorial Sloan Kettering in New York, N.Y., who had two patients with cases similar to the other two patients.

Raff says that they decided to gather these patients for the aforementioned case series published in the Journal of the Endocrine Society. Strikingly, as Greene et al. were working on their paper, another paper was published in Clinical Biochemistry by Donegan et al. titled “Corticotropin hormone assay interference: A case series.” “ACTH assay interference resulted in falsely elevated ACTH concentrations using the Siemens Immulite assay and consequently led to additional unnecessary testing,” the authors of that paper write.

“Erroneous results cause the misdiagnosis of disorders as well as miss critical diagnoses,” Raff says. “As we demonstrate in our paper, lack of diagnosis and misdiagnosis is problematic and unsafe, leading to unnecessary testing, procedures, and even surgery.”

“We can’t expect clinicians who have limited exposure to Cushing’s, or other hypothalamic–pituitary–adrenal axis conditions, to recognize that a result (like an ACTH value) may not fit with the rest of the clinical picture. This is challenging even for those of us who see Cushing’s patients in clinic every day. Until awareness is raised about the inaccuracies of the Immulite assay, clinicians will not know that they need to ‘trust but verify.’” — Eliza B. Geer, MD, Memorial Sloan Kettering, New York

Potential Safety Issues

Before going further, it should be made clear that the authors of the JES paper are in no way endorsing any particular ACTH assay, nor are they looking for any action to be taken against Siemens. In fact, according to Findling and a recent study by Shi et al. in Clinical Chemistry entitled “An Intact ACTH LC-MS/MS Assay as an Arbiter of Clinically Discordant Immunoassay Results”, fewer than 3% of patient samples return erroneous results on the Siemens Immulite assay. Still, inaccurate results can lead to very real complications. “The problem is that translates into some potential patient safety issues in those patients, even though it’s a small number of patients, particularly if the clinician who has ordered the assay doesn’t appreciate that these studies can be erroneous,” Findling says.

The clinical courses that the authors describe in their case series were markedly altered by erroneous results. Geer says that her two patients, for example, each were thought to have a chronic and potentially incurable diagnosis (occult ectopic Cushing) that turned out to be a condition curable by surgery (Cushing due to an adrenal nodule). “We highlight just a handful of people who have been affected by this problem; undoubtedly there are countless people whose clinical course is unknowingly heading down the wrong path because of inaccurate ACTH results as we describe in our paper,” she says.

Greene says that before the situation was clarified in the first patient, this patient sought out medical care  and  further testing at four different medical institutions.  This 21-year-old woman was put through a battery of tests, including three MRIs at two institutions. She underwent unnecessary petrosal sinus sampling that, in turn, had falsely elevated ACTH results, leading to invasive pituitary surgery. When her ACTH samples were analyzed again using a different assay, her ACTH levels were normal. “Additional follow-up data have confirmed that this patient did not have Cushing syndrome,” the authors write.

“When I presented this case at an interdisciplinary pituitary conference, another case from a different  institution was getting a ‘workup’ including an MRI ,” Greene says. “I have heard about a several more cases subsequently, whose workup was misled by this assay.”

Confounding Diagnoses

The authors tell Endocrine News that since “Assay-Specific Spurious ACTH Results Lead to Misdiagnosis, Unnecessary Testing, and Surgical Misadventure—A Case Series” was published, they have been contacted a number of times, from very experienced academic endocrinologists, for help clarifying test results that are confounding their diagnoses and overall clinical picture.

Gabrielle Page-Wilson, MD, of Columbia University in New York, a co-author of this paper, says that just last week, an endocrinologist contacted her regarding a patient with persistently elevated ACTH levels previously measured at ARUP Laboratories. The patient had seen a prior endocrinologist and had undergone extensive testing for both Cushing syndrome and adrenal insufficiency, which included multiple lab tests and pituitary imaging. The Immulite assay is prone to interference from heterophile antibodies, which can create both false positive and false negative results and can be blocked by removing immunoglobins. “Assay interference was suspected, and I recommended that the provider send a blood sample for ACTH to the Mayo Clinic where the Roche Cobas ACTH assay is in use, but she was unable to refer the sample to Mayo through her practice,” Page-Wilson says. “However, upon treatment of the patient’s plasma sample with polyethylene glycol (PEG), the ACTH level normalized, consistent with the precipitation of interfering immunoglobulins. This is just one of several similar cases underscoring the need to raise provider and institutional awareness of the limitations of the Immulite ACTH assay that is in common clinical use.” (ARUP Laboratories have since switched from the Immulite to the Roche Cobas ACTH assay.)

Geer, Greene, and Findling describe similar experiences: an endocrinologist reaches out about spuriously elevated ACTH results and is subsequently advised to seek results from alternate or multiple laboratories, which easily clarifies whatever “medical mystery” had been set off by the inaccurate test results. “This situation is dangerous for patients and leads to unnecessary and potentially dangerous workups for them,” Greene says.

Critical Thinking & Clinical Data

In the Discussion section of their paper, Greene et al., write that endocrinologists are very reliant on specialized test results. But why shouldn’t they be? Shouldn’t clinicians be able to trust assay results from well-established commercial laboratories? “While no assay is 100% sensitive and specific or immune from confounding interferences, clinical lab tests are generally held to high regulatory standards intended to ensure accuracy, specifically so that providers can feel comfortable trusting the results and using them to guide patient care,” Page-Wilson says. “It is always important for providers to think critically about clinical data, but it is equally important for commercial labs to use assay platforms that minimize the likelihood of unreliable results.”

Diagnosing and localizing Cushing syndrome can be challenging, and it involves the whole clinical picture – clinical presentation, comorbidities, differential diagnosis, lab testing, and finally identifying the primary source of the hormonal derangement, such as pituitary, ectopic, adrenal, etc.   “We can’t expect clinicians who have limited exposure to Cushing’s, or other hypothalamic–pituitary–adrenal axis conditions, to recognize that a result (like an ACTH value) may not fit with the rest of the clinical picture,” Geer says. “This is challenging even for those of us who see Cushing’s patients in clinic every day. Until awareness is raised about the inaccuracies of the Immulite assay, clinicians will not know that they need to ‘trust but verify.’”

What’s more, according to the authors, is the fact that in some cases, patients took it upon themselves to pursue further endocrine testing and definitive treatment. “Patients are savvy and smart, and of course they regularly consult Dr. Google,” Geer says. “Patients understandably seek treatment that they believe will help resolve their symptoms. Many people will seek evaluations with multiple practitioners, until they are offered the treatment they are looking for – even if this is the wrong treatment.”

Raff says that there is the general concept that all results on all tests from a clinical laboratory should always be evaluated with the notion that the result could be erroneous for a variety of reasons. He teaches his endocrine fellows to first repeat the test in the same lab if they think the result is incorrect and to make sure that the sample is drawn and processed correctly at the correct time of day and under the correct clinical circumstance (e.g. fasting vs. non-fasting, standing vs. sitting, etc). “I also tell them not to ignore an odd result,” he says. “It does take time and effort to request that the laboratory refer the sample to another laboratory using a different method but, as our paper references, this is the only way to resolve this problem efficiently.”

— Bagley is the senior editor of Endocrine News. He wrote about the joy of innovation in clinical practice in the November issue. 

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