The value of carbon dioxide combining power/potassium ratio in the etiological diagnosis of Cushing’s syndrome
Purpose: To evaluate the value of carbon dioxide combining power/potassium (CO2CP/K) ratio in etiological diagnosis of Cushing’s syndrome.
Materials and methods: Between 1994 and 2016, 226 patients with histologically confirmed Cushing’s syndrome were enrolled and investigated. The receiver operating characteristic (ROC) curve was analyzed.
Results: Patients (n=124) with Cushing’s disease had younger age (40.4±11.6 vs. 53.4±16.1 years), longer disease courses (24.0 vs. 3.0 months) and greater diastolic blood pressure (95±14 vs. 87±11 mmHg) than those (n=17) with ectopic adrenocorticotropic hormone (ACTH) syndrome (P<0.05). Compared with ACTH independent syndrome (n=85), ACTH dependent syndrome (n=141) had significantly (P<0.05) lower potassium (3.30±0.68 vs 3.58±0.62mmol/L) and chloride (101.8±5.2 vs. 104.3±4.2 mmol/L) but significantly (P<0.05) greater pH value, bicarbonate radicals, base excess, and CO2CP/K ratio (9.3±4.6 vs 7.5±2.4). Compared with patients with Cushing’s disease, patients with ectopic ACTH syndrome had significantly (P<0.05) lower potassium (2.33±0.54 vs. 3.42±0.59) and chloride (97.3±6.4 vs. 102.5±4.6 mmol/L) but significantly (P<0.05) greater pH value, bicarbonate radical, base excess, and CO2CP/K ratio (15.98±7.6 vs. 8.1±2.6). Analysis of the ROC curve with the ACTH dependent vs. independent syndrome demonstrated good diagnosis, with the cutoff point of the CO2CP/K ratio being 8.79, the sensitivity of 0.46, the specificity of 0.87 and the AUC of 0.61. Analysis of the ROC curve with the ectopic ACTH syndrome vs. Cushing’s disease revealed good diagnosis, with the cutoff point of CO2CP/K ratio being 12.45, the sensitivity of 0.65, the specificity of 0.95 and the AUC of 0.82.
Conclusion: The CO2CP/K ratio is useful in differentiating Cushing’s disease from the ectopic ACTH syndrome even though it has limited value in etiologically differentiating between ACTH dependent and independent Cushing’s syndrome.
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