Measurement of urinary free cortisol using the Acs:180 serum cortisol chemiluminescent immunoassay

Performance of LC-MS/MS and immunoassay based 24-h urine free cortisol in the diagnosis of Cushing's syndrome

24-h urine free cortisol (UFC) is an indicator of integrated cortisol secretion and established screening tool for Cushing's syndrome (CS). Doubts have been raised regarding specificity of immunoassays, and mass spectrometric techniques have been proposed as an alternative. In the present study we compared diagnostic accuracy of UFC measured with LC-MS/MS vs. immunoassay in patient with CS and patients where CS has been excluded. We examined 24-h urine samples from patients with surgically confirmed CS (n = 77; Cushing's disease (n = 44), ectopic CS (n = 5), adrenal CS (n = 28)) and patients in whom Cushing's syndrome was excluded (n = 97) by long-term follow up. UFC was first measured by automated chemiluminescence immunoassays (ADVIA Centaur, Siemens; LIAISON, DiaSorin). Aliquots of all samples were also analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Statistics: Passing-Bablok Regression, Receiver operating characteristic (ROC) analysis with Youden's index calculation. UFC of CS patients were higher with both immunoassays compared to LC-MS/MS (913 +/- 235 vs. 303 +/- 155 μg/24 h (ADVIA) and 898 +/-216 vs. 399 +/- 196 μg/24 h (LIAISON)). Similarly, UFC were higher with immunoassays than with LC-MS/MS in the control group (223 +/- 10 vs. 23 +/- 2 μg/24 h (ADVIA) and 105 +/- 6 vs. 27 +/- 4 ug/24 h for (LIAISON)). Passing-Bablok regression showed good correlation between LC-MS/MS and ADVIA as well as between LCMS/MS and LIAISON (r = 0.96 and r = 0.99, p < 000.1) but less correlation in controls (r = 0.83 and r = 0.74, respectively, p < 000.1). ROC calculation revealed the highest ROC AUC (0.89) for the LIAISON immunoassay, followed by LC-MS/MS (0.82) and the ADVIA (0.80). In direct comparison, AUCs from LC-MS/MS and immunoassays in the same patient were not statistically different (p < 0,001). Best cut-off concentration to identify patients with CS was 234 μg/24 h (LIAISON), 51 μg/24 h for LC-MS/MS and 330 μg/24 h (ADVIA Centaur). In summary, UFC values were measured substantially higher by both immunoassays compared to LC-MS/MS. This is most likely due to cross-reactivity from interfering glucocorticoid metabolites. Nevertheless, all three methods correlated well. ROC analysis revealed the highest AUC for one of the immunoassays, although differences between the three methods were not significant. Direct comparison with LC-MS/MS indicates that high diagnostic accuracy can be obtained with suitable immunoassays.

Suboptimal rise in awakening-induced cortisol is an accurate marker of cortisol insufficiency in patients with normal renal function (eGFR >60 mL/min)

Background The insulin tolerance test is the gold standard for diagnosis of cortisol insufficiency. However, it is cumbersome, invasive, requires supervised hospital facilities and has unpleasant side-effects. A non-invasive outpatient-based test will be useful. We hypothesized that free cortisol concentrations in multiple spot urine samples can be used to diagnose cortisol insufficiency in patients with normal renal function (eGFR > 60 mL/min). Method Patients and controls provided urine samples at bedtime (S1), and first (S2) and second (S3) void the next day. Cortisol and creatinine were measured in all three samples, and cortisol:creatinine ratio (S1, S2 and S3) was used for further analysis. The sum of S1 + S2 + S3 was used to calculate total cortisol secretion (T). Variation (V) in cortisol secretion in response to circadian rhythm was calculated as the modulus of the difference between S1 and S2 and S2 and S3. Results Samples were collected from 96 controls and 11 patients. S1 was significantly lower vs . S2 and S3 in controls ( P < 0.0001) but not in patients. S2, S3, T and V were significantly lower in patients vs . controls ( P < 0.0001). ROC curve analysis using insulin tolerance test as gold standard showed that S2, S3, T and V were all equally accurate diagnostic markers for cortisol insufficiency (AUC: 0.87, NPV: 100%). The best balance of sensitivity and specificity was achieved using T (sensitivity: 100%, specificity: 58%). Conclusion Multiple spot urine samples test is an accurate, relatively inexpensive, non-invasive, convenient outpatient-based screening test for exclusion of cortisol insufficiency.

Urinary corticoid concentrations measured by 5 different immunoassays and gas chromatography-mass spectrometry in healthy dogs and dogs with hypercortisolism at home and in the hospital

Background

Determination of the urinary corticoid‐to‐creatinine ratio (UCCR) is an important screening test in the diagnosis of hypercortisolism (HC). However, urinary cortisol metabolites interfere with cortisol measurement in immunoassays, leading to decreased specificity. Gas chromatography‐mass spectrometry (GC‐MS) is considered the gold standard for steroid hormone analysis, because it provides a high level of selectivity and accuracy.

Objectives

To prospectively compare the UCCR of healthy dogs and dogs with HC determined by 5 different immunoassays and by GC‐MS and to evaluate the influence of veterinary care on UCCR.

Animals

Twenty healthy dogs; 18 dogs with HC.

Methods

Urine was collected in the hospital and again after 6 days at home. Three chemiluminescence immunoassays (Access 2, Beckmann; Immulite 2000, DPC Siemens, with and without trichloromethane extraction) and 2 RIAs (Utrecht in house; Access Beckmann) were used. GC‐MS analyses were performed with Agilent 6890N/5973N. Urinary corticoid concentrations were related to urinary creatinine concentrations.

Results

Immunoassay results were significantly higher compared to GC‐MS results. Evaluation of bias plots and clinical assessment made on the basis of the assay results of each dog indicated substantial disagreement among the assays. Sensitivity varied from 37.5 to 75% and with selected assays was lower in samples from day 6 compared to day 0. GC‐MS was not superior to the immunoassays in discriminating healthy from HC dogs.

Conclusions and Clinical Importance

Considerable variation must be anticipated comparing different urinary cortisol assays. Establishing an assay‐ and laboratory‐specific reference range is critical when using UCCR.