The interpretive contribution of the baseline serum cortisol concentration of the ACTH stimulation test in the diagnosis of pituitary dependent hyperadrenocorticism in dogs

Diagnosis of naturally-occurring Cushing's syndrome by primary care veterinarians in selected European countries

BACKGROUND

Several tests are available to diagnose naturally-occurring Cushing's syndrome in dogs but there is a paucity of information on how primary care veterinarians (PCVs) use or interpret them.

OBJECTIVES

Determine how PCVs from selected European countries diagnose Cushing's syndrome in dogs.

METHODS

Cross-sectional survey study assessing testing protocols used by PCVs for screening and differentiation of Cushing's syndrome.

RESULTS

Two thousand one hundred and seventy-eight responses from 9 European countries were included. When Cushing's syndrome was suspected, 98.7% of respondents perform endocrine testing, whereas 1.2% rely on a treatment trial. Among the former, 59.9% reported performing screening tests in the absence of supportive clinical signs but with consistent clinicopathological abnormalities. Of 2150 respondents who performed endocrine testing, 66.6% report always using the same initial screening tests regardless of their pretest suspicion of disease. The tests most reported are the ACTH stimulation test (34.8%), low-dose dexamethasone suppression test (LDDST; 30.4%) or a combination of different tests (25.2%). In the absence of financial constraint, 1419 (66.0%) respondents always attempted differentiation, using abdominal ultrasonography (81.0%) and LDDST (46.1%). Overall, 69.8% of respondents reported offering referral to a specialist in ≤20% of cases suspected or diagnosed with Cushing's syndrome over the previous 5 years.

CONCLUSIONS AND CLINICAL IMPORTANCE

Testing protocols vary among PCVs. Almost 60% of respondents potentially screen dogs without consistent clinical signs, raising concerns for overdiagnosis. A proportion never attempt differentiation, which likely affects prognosis. Cases are rarely referred to a specialist, reflecting that Cushing's syndrome is mainly managed in primary care practices. These results suggest that there is room for further education of PCVs.

Mechanism of long-term high-dose prednisolone administration producing myocardial fibrosis in beagle dogs

Background

We previously reported that myocardial fibrosis may be one of the causes of left ventricular hypertrophy and cardiac dysfunction in dogs with hyperglucocorticism (HGC). The detailed mechanism by which myocardial fibrosis of the left ventricle occurs in dogs with HGC remains unclear.

Aim

Th is study investigated the mechanism by which HGC causes fibrosis of the left ventricle.

Methods

The impa cts of HGC on the heart by comparing samples obtained from high-dose glucocorticoid (GC)-treated (P) and untreated (C) dogs. The P group included healthy Beagle dogs (n = 6) treated with prednisolone (2 mg/kg, bid, po) for 84 days, and the C group included healthy Beagle dogs (n = 6) euthanized for unrelated reasons. In three of the P group dogs, serum was collected before the start of administration (Day 0) and on Day 84 to measure angiotensin II concentrations and oxidative stress markers (8-hydroxy-2'-deoxyguanosine (8OHdG), NADPH oxidase, and superoxide levels). Samples of the left ventricular free wall (LVFW), right ventricular free wall (RVFW), interventricular septum (IVS), and aortic root were harvested from both groups (n = 6 for each group). Using these tissue samples, angiotensin II type 1 receptor (AT1R), 8OHdG, and transforming growth factor β1 (TGFβ1) immunohistochemical stains were performed.

Results

The blood N ADPH oxidase concentration was significantly higher (p = 0.027) in the P group 84 days after initiation of the medication compared to that before prednisolone treatment. By contrast, there was no significant difference in serum angiotensin II (p = 0.450), 8OHdG (p = 0.068), and superoxide (p = 0.057) concentrations. The positive staining rates of AT1R, 8OHdG, and TGFβ1 in the heart (LVFW, RVFW, IVS, and aortic root) were significantly higher in the P group than those in the C group.

Conclusion

Angiotensin II and oxidative stress in HGC may cause left ventricular fibrosis in dogs.

Canine noninflammatory alopecia: An approach to its classification and a diagnostic aid

Noninflammatory alopecia is common in dogs and is a frequent cause to consult a veterinarian. It is also a common reason to take biopsies. Noninflammatory alopecia can be attributed to a decreased formation or cytodifferentiation of the hair follicle or the hair shaft in utero, resulting in congenital alopecia. Congenital alopecia often has a hereditary cause, and examples of such disorders are ectodermal dysplasias associated with gene variants of the ectodysplasin A gene. Noninflammatory alopecia may also be caused by impaired postnatal regeneration of hair follicles or shafts. Such disorders may have a clear breed predilection, and alopecia starts early in life. A hereditary background is suspected in those cases but has not been proven. They are referred to as follicular dysplasia although some of these disorders present histologically like a hair cycle disturbance. Late-onset alopecia is usually acquired and may be associated with endocrinopathies. Other possible causes are impaired vascular perfusion or stress. As the hair follicle has limited possible responses to altered regulation, and histopathology may change during the course of a disease, a detailed clinical history, thorough clinical examination including blood work, appropriate biopsy site selection, and detailed histological findings need to be combined to achieve a final diagnosis. This review aims to provide an overview about the known noninflammatory alopecic disorders in dogs. As the pathogenesis of most disorders is unknown, some statements are based on comparative aspects or reflect the authors' opinion.

Adrenocorticotropic hormone-producing pituitary adenoma with pituitary apoplexy treated by surgical decompression: a case report

Background

Pituitary-dependent hypercortisolism (PDH) is one of the most common endocrine disorders in veterinary medicine. However, there are few reports on pituitary tumor apoplexy (PTA) in dogs and no reports on its surgical intervention in veterinary medicine. Accordingly, the appropriate treatment is unknown. Herein, a case of PDH and PTA in a dog treated surgically is described.

Case presentation

A mongrel female dog (spayed; age, 8 years and 8 months; weight, 6.1 kg) with persistently elevated alkaline phosphatase underwent adrenocorticotropic hormone (ACTH) stimulation testing (post-stimulation cortisol: 20.5 μg/dL), abdominal ultrasonography (adrenal gland thickness: left, 5.7 mm; right, 8.1 mm), and brain magnetic resonance imaging (MRI) (pituitary-to-brain ratio [PBR], 0.61) at the referral hospital, resulting in a diagnosis of PDH (day 0). On day 9, the dog visited XXXX for the preparation of pituitary surgery to treat PDH. However, on days 10–15, the dog developed a loss of energy and appetite, bloody diarrhea, vomiting, and a decreased level of consciousness. However, on day 16, the dog’s condition recovered. A preoperative MRI scan performed on day 52 (the day of surgery) showed apoplexy in the dorsal pituitary region (PBR, 0.68). Based on the PTA findings, the risks of surgery were described to the owner, and approval was obtained. At the time of trans-sphenoidal surgery, a partial pituitary resection was performed with preservation of the PTA area due to adhesions between the PTA area of the right side of the pituitary and surrounding tissues. The resected pituitary tissue was diagnosed as an ACTH-producing adenoma, with necrotic and hemorrhagic findings. As of day 290, endogenous ACTH and cortisol levels did not exceed the reference range.

Conclusions

The acute signs that occurred on days 10–15 were most likely caused by PTA. Therefore, when signs similar to those detected in acute hypoadrenocorticism are observed in dogs with PDH, it is necessary to include PTA as a differential diagnosis. Trans-sphenoidal surgery may be effective in PDH-affected dogs that develop PTA, but careful attention should be paid to tissue adhesions secondary to hemorrhage that may occur after PTA.

Evaluation of the ACTH stimulation test using a low dose of a depot formulation in healthy dogs and in dogs with untreated Cushing's syndrome

The sensitivity of the adrenocorticotropic hormone (ACTH) stimulation test to detect Cushing's Syndrome (CS) using a depot formulation needs to be evaluated. The aims of this study were to propose a reference interval (RI) for cortisol values 1-hour after administration of a low-dose of depot ACTH in healthy dogs, and to evaluate the sensitivity of this test to detect CS, differentiating among types of CS based on ultrasound findings. Forty-one healthy dogs (20 males, 21 females) were prospectively included. Additionally, 90 dogs with CS (31 males, 59 females) were retrospectively included. Dogs with CS were ultrasonographically classified as follows: 44 dogs with symmetrical adrenomegaly consistent with pituitary-dependent hypercortisolism (PDH), 8 dogs with unilateral adrenomegaly and atrophy of the contralateral adrenal gland or unilateral or bilateral adrenomegaly with malignancy features consistent with adrenal-dependent hypercortisolism (ADH), 34 dogs with equivocal adrenal asymmetry (EAA) and 4 dogs with normal adrenal thickness. In healthy dogs, lower and upper limit of the 95% RI for 1-hour post-ACTH cortisol concentration and their 90% confidence intervals, were 4.4 (2.7-5.8) μg/dl and 18.4 (16.5-20.0) μg/dl, respectively. Post-ACTH cortisol concentration was above the RI in 90.0% (ci95%, 76.1-100) of dogs with CS. An elevated post-ACTH cortisol concentration was detected in 95.5% (ci95%, 76.1-100) of dogs with PDH, 62.5% (ci95%, 46.1-78.9) of dogs with ADH and 88.2% (ci95%, 69.1-100) of dogs with EAA. The sensitivity of the ACTH stimulation test using a low-dose of depot ACTH in high in dogs with CS.

Inverse relationship between eosinophil profiles and serum glucose concentration in dogs with naturally occurring hypercortisolism

Hyperglycemia and eosinopenia are well-known characteristics of hypercortisolism (HC) in humans, however, their association in dogs with HC has rarely been reported. This study aimed to evaluate the association between eosinophils and serum fasting glucose concentration in dogs with HC. Forty-seven dogs with HC and 43 dogs with non-adrenal illness were included. In this retrospective cohort study, the complete blood count, blood chemistry profile, and pre- and post-adrenocorticotropic hormone (ACTH) cortisol concentrations were analyzed. Significant differences were found in neutrophil, monocyte, eosinophil, and platelet counts; eosinophil percentage; neutrophil-to-lymphocyte ratio; aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyl transferase activities (P < 0.05) between the groups. In dogs with HC, the eosinophil percentage was inversely correlated with fasting blood glucose (r = -0.3515, P = 0.0154) and post-ACTH cortisol concentrations (r = -0.6509, P < 0.0001). The neutrophil-to-lymphocyte ratio was inversely correlated with the eosinophil percentage (r = -0.4573, P = 0.0012) and count (r = -0.3688, P = 0.0108), but positively correlated with the fasting blood glucose level (r = 0.3888, P = 0.0069). Such correlations were not identified in dogs with non-adrenal illness. A multivariate analysis showed that only eosinophil percentage was associated with the presence of hyperglycemia in dogs with HC (odds ratio = 2.100, 95% confidence interval = 1.051-4.199, P = 0.0360). Therefore, eosinopenia induced by excess cortisol might be associated with altered glucose metabolism in dogs with HC. A better understanding of this correlation could be valuable to predict and prevent the complications of HC.

Frequency and risk factors for naturally occurring Cushing's syndrome in dogs attending UK primary-care practices

Objectives

To estimate the frequency and risk factors for Cushing's syndrome in dogs under UK primary veterinary care.

Materials and Methods

Dogs with Cushing's syndrome were identified by searching electronic patient records of primary‐care veterinary practices. Pre‐existing and incident cases of Cushing's syndrome during 2016 were included to estimate the 1‐year period prevalence. Incident cases were used to estimate the annual incidence and to identify demographic risk factors for the diagnosis of Cushing's syndrome in dogs, through multivariable logistic regression.

Results

Analysis included 970 pre‐existing and 557 incident cases of Cushing's syndrome from a population of 905,544 dogs. The estimated 1‐year period prevalence for Cushing's syndrome in dogs under veterinary care was 0.17% (95% confidence interval 0.16 to 0.18) and incidence was 0.06% (95% confidence interval 0.05 to 0.07). In multivariable logistic regression modelling, the Bichon frise (odds ratio=6.17, 95% confidence interval 4.22 to 9.00), Border terrier (5.40, 95% confidence interval 3.66 to 7.97) and Miniature schnauzer (3.05, 95% confidence interval 1.67 to 5.57) had the highest odds of Cushing's syndrome. The Golden retriever (0.24, 95% confidence interval 0.06 to 0.98) and Labrador retriever (0.30, 95% confidence interval 0.17 to 0.54) were the most protected breeds. Increasing age, bodyweight greater than the breed‐sex mean and being insured also showed increased odds of Cushing's syndrome.

Clinical Significance

As Cushing's syndrome is predominately diagnosed and managed in primary‐care practice, this study provides valuable new information of its epidemiology in this setting. Demographics reported are supportive of previous work and additional novel associations identified, such as the Border terrier, could enhance the index of suspicion for veterinarians.

Utility of a corticotropin-releasing hormone test to differentiate pituitary-dependent hyperadrenocorticism from cortisol-producing adrenal tumors in dogs

Background

Hyperadrenocorticism (HAC) is a common endocrine disorder in dogs; however, there are no reports on the use of the corticotropin‐releasing hormone test (CRHT) to differentiate between pituitary‐dependent hyperadrenocorticism (PDH) and cortisol‐producing adrenal tumors (CPATs), both causative of HAC.

Objectives

To evaluate the usefulness of CRHT as a tool to differentiate between PDH and CPAT in dogs and to determine the reference intervals for CRHT in healthy, PDH, and CPAT dogs.

Animals

Dogs diagnosed with PDH (n = 21), CPAT (n = 6), and healthy beagle dogs (n = 33).

Methods

This prospective study included dogs with a definitive diagnosis of PDH and CPAT and healthy beagle dogs, in which CRHT was performed, were prospectively evaluated. We investigated the correlations of CRHT (endogenous adrenocorticotropic hormone [ACTH] concentration, endogenous ACTH concentration [EAC], and poststimulation ACTH concentration [PAC]) with pituitary‐to‐brain ratio (PBR) (in PDH) and with indices of adrenal ultrasonography (smaller and larger adrenal gland dorsoventral thickness in PDH and CPAT).

Results

For EAC, the area under the curve (AUC) was 0.95, with a cutoff value of 26.3 pg/mL (sensitivity: 90.62%, specificity: 87.50%). The AUC for PAC was 0.96 with a cutoff value of 54.5 pg/mL (sensitivity: 100.00%, specificity: 66.67%). The 95% reference interval for CRHT in healthy (control) dogs ranged 5.00 to 79.8 pg/mL (1.10‐17.57 pmol/L) for EAC, and 1.92 to 153.42 pg/mL (0.42‐33.78 pmol/L) for PAC. There was no significant correlation between PBR and CRHT, nor adrenal size and CRHT.

Conclusions and Clinical Importance

CRHT appears to be a rapid and reliable test for differentiating PDH from CPAT in dogs.

Validation study of canine serum cortisol measurement with the Immulite 2000 Xpi cortisol immunoassay

We report the results of validation of canine serum cortisol determination with the Immulite 2000 Xpi cortisol immunoassay (Siemens), with characterization of precision (CV), accuracy (spiking-recovery [SR] bias), and observed total error (TEo = bias + 2CV) across the reportable range, specifically at the most common interpretation thresholds for dynamic testing. Imprecision increased at increasing rate with decreasing serum cortisol concentration and bias was low, resulting in increasing TEo with decreasing serum cortisol concentration. Inter-laboratory comparison study allowed for determination of range-based bias (RB) and average bias (AB). At 38.6 and 552 nmol/L (1.4 and 20 μg/dL), between-run CV was 10% and 7.5%, respectively, and TEo ~30% and ~20%, respectively (TEo remained similar regardless of the considered bias: SR, RB, or AB). These analytical performance parameters should be considered in the interpretation of results and for future expert consensus discussions to determine recommendations for allowable total error (TEa). Importantly, the commonly used thresholds for interpretation of results were determined ~40 y ago with different methods of measurements and computation, hence updating is desirable. Quality control material (QCM) had between-run imprecision of 4% for QCM1 and 7% for QCM2; the bias was minimal for both levels. Acceptable QC rules are heavily dependent on the desired TEa for the QCM system (TEaQCM), itself limited by the desired clinical TEa. At low TEaQCM (20-33%), almost no rules were acceptable, whereas at high TEaQCM (50%), almost all rules were acceptable; further investigation is needed to determine which TEaQCM can be guaranteed by simple QC rules.

Machine-learning based prediction of Cushing's syndrome in dogs attending UK primary-care veterinary practice

Cushing’s syndrome is an endocrine disease in dogs that negatively impacts upon the quality-of-life of affected animals. Cushing’s syndrome can be a challenging diagnosis to confirm, therefore new methods to aid diagnosis are warranted. Four machine-learning algorithms were applied to predict a future diagnosis of Cushing's syndrome, using structured clinical data from the VetCompass programme in the UK. Dogs suspected of having Cushing's syndrome were included in the analysis and classified based on their final reported diagnosis within their clinical records. Demographic and clinical features available at the point of first suspicion by the attending veterinarian were included within the models. The machine-learning methods were able to classify the recorded Cushing’s syndrome diagnoses, with good predictive performance. The LASSO penalised regression model indicated the best overall performance when applied to the test set with an AUROC = 0.85 (95% CI 0.80–0.89), sensitivity = 0.71, specificity = 0.82, PPV = 0.75 and NPV = 0.78. The findings of our study indicate that machine-learning methods could predict the future diagnosis of a practicing veterinarian. New approaches using these methods could support clinical decision-making and contribute to improved diagnosis of Cushing’s syndrome in dogs.

Long-term administration of prednisolone: Effects on the myocardial tissue of healthy beagle dogs

This study aimed to assess the structural and functional effects of long-term hyperglucocorticoidemia on canine myocardium and compare these parameters with histopathological changes. Twelve healthy male beagle dogs were enrolled and assigned to the high-dose prednisolone (P; n=6) and control (C; n=6) groups. The P group was treated with 2 mg/kg of prednisolone BID for 84 days. Clinical parameters were measured using echocardiography and non-invasive systolic blood pressure (SBP) measured before the initiation of synthetic corticosteroids and at 7, 28, 56, and 84 days after the start of medication. For histological evaluation, cardiovascular tissue was harvested from dogs in groups P (at the end of the medication period) and C (scheduled to be euthanized for unrelated reasons). In the P group, clinical changes including thickening of the left ventricular free wall (LVFW) and interventricular septum (IVS), decreased left ventricular (LV) diastolic function, and increased SBP were observed after the start of medication. During histological evaluation, fibrosis was observed in the LVFW and IVS in the P group. Furthermore, decreased glucocorticoid receptor (GCR) levels were observed in the LVFW, right ventricular free wall (RVFW), and IVS and increased mineralocorticoid receptor (MCR) levels were observed in the LVFW and RVFW in the P group compared with those in the C group. In conclusion, fibrosis may cause LV structural and functional abnormalities in dogs with hyperadrenocorticism. Furthermore, GCR downregulation and upregulated MCR might influence the myocardial fibrosis.

Development and internal validation of a prediction tool to aid the diagnosis of Cushing's syndrome in dogs attending primary-care practice

BACKGROUND

Novel methods to aid identification of dogs with spontaneous Cushing's syndrome are warranted to optimize case selection for diagnostics, avoid unnecessary testing, and ultimately aid decision-making for veterinarians.

HYPOTHESIS/OBJECTIVES

To develop and internally validate a prediction tool for dogs receiving a diagnosis of Cushing's syndrome using primary-care electronic health records.

ANIMALS

Three hundred and ninety-eight dogs diagnosed with Cushing's syndrome and 541 noncase dogs, tested for but not diagnosed with Cushing's syndrome, from a cohort of 905 544 dogs attending VetCompass participating practices.

METHODS

A cross-sectional study design was performed. A prediction model was developed using multivariable binary logistic regression taking the demography, presenting clinical signs and some routine laboratory results into consideration. Predictive performance of each model was assessed and internally validated through bootstrap resampling. A novel clinical prediction tool was developed from the final model.

RESULTS

The final model included predictor variables sex, age, breed, polydipsia, vomiting, potbelly/hepatomegaly, alopecia, pruritus, alkaline phosphatase, and urine specific gravity. The model demonstrated good discrimination (area under the receiver operating curve [AUROC] = 0.78 [95% CI = 0.75-0.81]; optimism-adjusted AUROC = 0.76) and calibration (C-slope = 0.86). A tool was developed from the model which calculates the predicted likelihood of a dog having Cushing's syndrome from 0% (score = -13) to 96% (score = 10).

CONCLUSIONS AND CLINICAL IMPORTANCE

A tool to predict a diagnosis of Cushing's syndrome at the point of first suspicion in dogs was developed, with good predictive performance. This tool can be used in practice to support decision-making and increase confidence in diagnosis.

Diagnostic contribution of individual components of adrenal function tests to diagnose canine hyperadrenocorticism

There is limited information regarding the value of constitutive components of the ACTH stimulation test (ACTHST) and low-dose dexamethasone suppression test (LDDST) including serum baseline cortisol (BC), difference between post-ACTH stimulation cortisol (PC) and BC (ΔACTHC), cortisol concentration 4h after dexamethasone administration (4HC), difference between 4HC and BC (Δ4C), and the difference between cortisol concentration 8h after dexamethasone administration and 4HC (Δ8C). Therefore, the objective of this study was to determine if these components can predict hyperadrenocorticism, pituitary-dependent hyperadrenocorticism (PDH), or functional adrenocortical tumor (FAT) in dogs. Cortisol concentrations were normalized, as fold change (FC), to the PC reference interval upper limit. A total of 1267 dogs were included, with hyperadrenocorticism diagnosed in 537 (PDH, n=356; FAT, n=28; undetermined, n=153) and excluded in 730. The area under the receiver operating curves for BC, ΔACTHC, 4HC, Δ4C, and Δ8C to predict hyperadrenocorticism were 0.76 (95% confidence interval (CI), 0.73-0.79), 0.91 (95% CI, 0.89-0.93), 0.83 (95% CI, 0.80-0.87), 0.55 (95% CI, 0.50-0.60), and 0.67 (95% CI, 0.62-0.72), respectively. A diagnostic limit of ≥0.78 FC for ΔACTHC had excellent sensitivity (1.00; 95% CI, 0.74-1.00), but poor specificity (0.67; 95% CI, 0.64-0.71), to predict FAT in dogs with a positive ACTHST. A diagnostic limit of ≥-0.26 FC for Δ4C had excellent sensitivity (1.00; 95% CI, 0.79-1.00), but poor specificity (0.21; 95% CI, 0.18-0.26), to predict FAT in dogs with a positive LDDST. In hyperadrenocorticoid dogs that have positive ACTHST or LDDST results, ΔACTHC or Δ4C, respectively, could be used to exclude FAT.

Diagnosis of spontaneous hyperadrenocorticism in dogs. Part 2: Adrenal function testing and differentiating tests

Hyperadrenocorticism is a relatively common endocrine disorder in dogs that has been extensively described. However, its diagnosis remains challenging because there is no true reference standard test, and a myriad factors can affect the diagnostic performance of the commonly used adrenal function tests. Ultimately, the diagnosis is based on a combination of signalment, history and clinical findings, and a variety of diagnostic test results. The second part of this review aims to appraise available data on diagnostic performance of adrenal function tests in naturally occurring canine hyperadrenocorticism.

Diagnosis of spontaneous hyperadrenocorticism in dogs. Part 1: Pathophysiology, aetiology, clinical and clinicopathological features

Hyperadrenocorticism is a relatively common endocrine disorder in dogs. It occurs as a result of a functional pituitary or adrenal tumour, although other causes have been rarely reported. Canine hyperadrenocorticism has been extensively described but diagnosing this disease remains challenging. Few studies have investigated the clinical and clinicopathological features helpful in differentiating dogs with hyperadrenocorticism from dogs in which the disease is suspected but eventually excluded. Ultimately the diagnosis is based on a combination of multiple pieces of information emanating from the signalment, history, clinical findings, and a variety of diagnostic tests. The first part of this review aims to critically appraise the available data on epidemiology, clinical and laboratory features of naturally occurring canine hyperadrenocorticism.

The interpretive contribution of the baseline serum cortisol concentration of the ACTH stimulation test in the diagnosis of pituitary dependent hyperadrenocorticism in dogs

Background

Current recommendation for performing the ACTH stimulation test (ACTHST) for diagnosis of hyperadrenocorticism (HAC) advocates the collection of baseline serum cortisol concentration (BC), but no references for interpretation of its results exist.

Objective

Evaluate the contribution of BC of the ACTHST to the diagnosis of HAC.

Animals

Fifty‐four dogs were evaluated for suspected HAC at a referral hospital.

Methods

Records of dogs that had been evaluated by ACTHST for suspected HAC were reviewed. Receiver operator characteristics (ROC) analyses were used to assess the performance of BC, post‐stimulation serum cortisol concentrations (PC), post‐to‐baseline cortisol concentration difference (DeltaC) and quotient (RatioC) for the diagnosis of HAC by comparing the area under the ROC curve (AUC) of PC to each of the other tests.

Results

The AUC of PC (95% confidence interval [CI]: 0.92; 95% CI, 0.81‐0.98) was significantly higher than AUCs of BC (0.70; 95% CI, 0.56‐0.82; P = .01) and RatioC (0.55; 95% CI, 0.41‐0.69; P < .001), and was not significantly different from AUC of DeltaC (0.86; 95% CI, 0.74‐0.94; P = .09). An optimal cutoff value of 683 nmol/L (24.8 μg/dL) for PC yielded a sensitivity of 86% and a specificity of 94%, respectively, and a cutoff value of 718 nmol/L (26.0 μg/dL) yielded a specificity of 100% with of 81% sensitivity for the diagnosis of pituitary‐dependent HAC.

Conclusion and Clinical Importance

The PC had good discriminatory ability for the diagnosis of HAC. It was comparable to DeltaC, whereas BC and RatioC were ineffective. Current recommendations to collect samples for BC appear redundant.