We use cookies to understand how you use our site and to improve your experience. This includes personalizing content and advertising. To learn more, click here. By continuing to use our site, you accept our use of cookies. Cookie Policy.

Features Partner Sites Information LinkXpress hp
Sign In
Advertise with Us
LGC Clinical Diagnostics

Download Mobile App




Diagnostic Options When Standard Tests Are Inconclusive

By LabMedica International staff writers
Posted on 18 Oct 2017
Print article
Image: Immunostaining for nuclear p21 on a pituitary tumor. ACTH-secreting adenoma without cytoplasmic staining (Photo courtesy of the William Harvey Research Institute).
Image: Immunostaining for nuclear p21 on a pituitary tumor. ACTH-secreting adenoma without cytoplasmic staining (Photo courtesy of the William Harvey Research Institute).
The diagnosis of Cushing’s disease, the predominant endogenous form of Cushing’s syndrome, requires a laboratory strategy that sequentially rules out potential causes of excess cortisol until the correct one is identified.

After ruling out exogenous causes of Cushing’s-like symptoms, the first step is to document cortisol excess. Blood cortisol concentration exhibits diurnal variation, so it is less useful than 24-hour urinary free cortisol, which the Endocrine Society (Washington, DC, USA) recommends for demonstrating overproduction of the hormone.

The other two recommended screening tests are salivary cortisol and the 1 mg overnight dexamethasone suppression test. If two of these three screening tests are abnormal, further investigation should be undertaken. If elevated adrenocorticotropic hormone (ACTH) is detected, this suggests an ACTH-dependent form of Cushing’s syndrome. About 30% of Cushing’s syndrome cases are ACTH-independent, but among ACTH-dependent cases, nearly all are caused by an ACTH-secreting pituitary adenoma and classified as Cushing’s disease. The remainder of ACTH-dependent cases is due to ectopic ACTH producing tumors, which are very rare and usually occur in the lungs or thymus, although they have also been described in the thyroid, ovaries, liver, and adrenal glands.

A high-dose dexamethasone suppression test helps determine if the case is Cushing’s disease or caused by ectopic ACTH production. High doses of dexamethasone often suppress ACTH production by pituitary adenomas, whereas no suppression occurs in ectopic tumors. Stimulation with corticotropin releasing hormone (CRH) also tends to exaggerate ACTH release in Cushing’s disease, whereas ectopic tumors respond poorly or not at all. In a small fraction of cases, however, the results of all of these tests are non-diagnostic. When this occurs, bilateral inferior petrosal sinus sampling (BIPSS) is needed to verify that the source of ACTH is the pituitary gland.

It has been reported that in patients with an ectopic ACTH producing tumor, the ratio of IPS: venous ACTH concentrations will be less than 1.4:1. In patients with Cushing’s disease, the ratio will exceed 2.0, with averages near 15. The sensitivity and specificity of BIPSS for Cushing’s disease are 88%-100% and 67%-100%, respectively. A less invasive procedure, jugular vein sampling (JVS), has been proposed. JVS has similar sensitivity and specificity to BIPSS, but when JVS results are negative, BIPSS is still recommended as the definitive test. The review written by Roger L. Bertholf, PhD, DABCC, FACB, from Houston Methodist Hospital in Texas (TX, USA) was published on October 1, 2017, in Clinical Laboratory News.

Related Links:
Endocrine Society
Houston Methodist Hospital

New
Gold Member
Rotavirus Test
Rotavirus Test - 30003 – 30073
Verification Panels for Assay Development & QC
Seroconversion Panels
New
Dermatophytosis Rapid Diagnostic Kit
StrongStep Dermatophytosis Diagnostic Kit
New
Coagulation Analyzer
CS-2400

Print article

Channels

Molecular Diagnostics

view channel
Image: Researcher Kanta Horie places a sample in a mass spectrometer that measures protein levels in blood plasma and other fluids (Photo courtesy of WashU Medicine)

Highly Accurate Blood Test Diagnoses Alzheimer’s and Measures Dementia Progression

Several blood tests are currently available to assist doctors in diagnosing Alzheimer's disease in individuals experiencing cognitive symptoms. However, these tests do not provide insights into the clinical... Read more

Immunology

view channel
Image: The findings were based on patients from the ADAURA clinical trial of the targeted therapy osimertinib for patients with NSCLC with EGFR-activated mutations (Photo courtesy of YSM Multimedia Team)

Post-Treatment Blood Test Could Inform Future Cancer Therapy Decisions

In the ongoing advancement of personalized medicine, a new study has provided evidence supporting the use of a tool that detects cancer-derived molecules in the blood of lung cancer patients years after... Read more

Microbiology

view channel
Image: Schematic representation illustrating the key findings of the study (Photo courtesy of UNIST)

Breakthrough Diagnostic Technology Identifies Bacterial Infections with Almost 100% Accuracy within Three Hours

Rapid and precise identification of pathogenic microbes in patient samples is essential for the effective treatment of acute infectious diseases, such as sepsis. The fluorescence in situ hybridization... Read more
Copyright © 2000-2025 Globetech Media. All rights reserved.