Low dose ACTH test--a word of caution

Technical details influence the diagnostic accuracy of the 1 microg ACTH stimulation test

OBJECTIVE

To examine the factors causing inadequate cortisol responses to the 1 microg ACTH stimulation test.

DESIGN

Random test assignment (by age and gender) at 0800 or 1600 h.

METHODS

We recruited 20 healthy adults to each of the three age groups (<40 years, 40-55 years, and >55 years; half females in each group). ACTH stimulation tests were performed in an outpatient clinic at the NIH Clinical Research Center. Plasma cortisol was measured just before, and 30 and 60 min after the administration of 1 microg ACTH (1-24). The ACTH concentration in diluted and administered solutions was measured.

RESULTS

Twenty-five volunteers (19 at 1600 h) had a subnormal cortisol response (peak cortisol 10.4-17.5 microg/dl), using a criterion <18 microg/dl (497 nmol/l), for a specificity of 58% (confidence interval (CI) 45-71%). Afternoon testing had a significant impact on failure rates (odds ratio 6.98, CI 2.17-22.43), while gender and age did not. The stock solution contained 1 microg ACTH, but after administration through tubing it contained only 0.5-0.8 microg.

CONCLUSIONS

The high rate of abnormal results, especially in the afternoon, and loss of ACTH through tubing suggest that morning testing and minimal tubing should be adopted to avoid an inappropriate diagnosis of adrenal insufficiency. Earlier time points and standardized protocols would facilitate comparison of studies.

Repeatability of the low-dose ACTH test in asthmatic children on inhaled corticosteroids

AIM

To assess the repeatability of low-dose Synacthen test (LDST) in asthmatic children receiving high-dose fluticasone propionate (FP).

METHODS

Low-dose Synacthen test was performed on 18 children with stable chronic asthma treated with FP at a constant daily dose of > or =500 microg and repeated 1 month later. Repeatability was assessed using the Kappa statistic for categorical variables.

RESULTS

Fifteen patients had consistent results (either two normal or two abnormal responses) and three patients had inconsistent results (one normal and one abnormal response). The Kappa statistic was 0.56 indicating fair to good agreement between the tests.

CONCLUSION

The results of adrenal function testing in patients on inhaled steroids can have major implications for patient management, making it important to use a test with excellent repeatability. The LDST conducted using our protocol does not fulfil this criterion.

Assessing adrenal function in primary care settings with a single sample subcutaneous glucagon test

OBJECTIVE

To test the efficacy of the low-dose glucagon test in assessing adrenal gland function.

STUDY DESIGN

Subcutaneous glucagon was used to assess the hypothalamo-pituitary-adrenal gland (HPA) axis in 215 healthy children. Concordance of this test with the low-dose intravenous ACTH test was established for 42 children. Glucagon testing was conducted for 150 minutes after subcutaneous glucagon administration and for 30 minutes after 1 microg intravenous ACTH.

RESULTS

Mean peak serum cortisol concentrations were 22.4 +/- 0.6 microg/dL (SEM) after subcutaneous glucagon and 20.0 +/- 0.6 microg/dL after intravenous ACTH. Specificity of 95% was found at peak cortisol concentrations of 9.5 and 12.5 microg/dL for the glucagon and ACTH tests, respectively. Concordance between the glucagon and ACTH tests was 90.5%.

CONCLUSIONS

The glucagon test was found to be as good a test of the HPA axis as the ACTH test and had a 90.5% concordance with it. The ease of performing the glucagon test, namely, obtaining a single sample of blood 150 minutes after the subcutaneous administration of glucagon, makes it a useful method of assessing the HPA axis in primary care settings.

Repetitive graded ACTH stimulation test for adrenal insufficiency

ACTH stimulation is useful in assessing the hypothalamo-pituitary-adrenal axis. However, there is still some debate about the proper dose and interpretation. We designed a new protocol using repetitive graded ACTH stimulation. Thirty-two patients with the diagnosis of adrenal insufficiency (Al) were studied. After taking samples for baseline ACTH and cortisol, 1 microg fresh-prepared ACTH (Synacthen (1-24)) was injected intravenously, then 5, 50 and 100 microg at hourly interval. Cortisol responses were measured at 30, 60, 120, 180 and 240 min. The secondary Al group (26 subjects) had cortisol responses in between those of the control group (8 subjects) and the primary Al group (6 subjects). The minimal overlap between the secondary Al group and the control group occurred at a 30-min cortisol response after 1 microg ACTH stimulation, using 20 microg/dl as the cut-off level. There was only one exception which showed an episodic release at 30 min. There were 5, 10 and 9 patients with secondary Al who responded normally to 5, 50 and 100 microg ACTH stimulation, respectively. Maximal cortisol increments of the primary Al group were all below 4 microg/dl. Although there were 11 cases of secondary Al whose cortisol responses overlapped with those of primary Al, only two of them had a cortisol increment less than 4 microg/dl. Our new protocol combines the advantage of the low dose ACTH stimulation test, a sensitive method for detecting mild Al, and the ACTH infusion test, a longer test to mimic surgical stress.

Reproducibility of the cortisol response to stimulation with the low dose (1 microg) of ACTH

OBJECTIVE

Previous studies have shown that the rapid ACTH stimulation test using a low dose of 1 microg is more sensitive than that using 250 microg ACTH for detecting subtle cases of adrenal insufficiency. However, there are controversies for the reproducibility of the 1 microg-test. To evaluate the reproducibility of the 1 microg-test, we assessed both day-to-day and diurnal variations of cortisol responses to 1 microg ACTH injection. In addition, optimum sampling time for the 1 microg-test was also determined.

SUBJECTS

AND DESIGN Eight healthy volunteers and five patients with secondary adrenal insufficiency were recruited. Healthy subjects were given 1 microg ACTH 3 times in the morning (0800 h) and 2 times in the afternoon (1600 h). Patients with adrenal insufficiency had 2-tests in the morning and 2 in the afternoon. Serum cortisol levels were measured every 10 minutes for 1 h after the injection.

RESULTS

In healthy subjects, basal and peak serum cortisol levels were significantly higher in the morning (P < 0.05), whereas maximum cortisol increments were higher in the afternoon (P < 0.001). In patients with adrenal insufficiency, basal and peak serum cortisol levels in the morning were not different from corresponding values in the afternoon. Intra-individual coefficient of variation (CV) of peak serum cortisol response to 1 microg ACTH ranged from 3.0 to 16.4% in healthy subjects and 10.0-34. 4% in patients. Also, there was a significant correlation between peak morning or afternoon cortisol levels after 1 microg ACTH injection given in different days in both healthy subjects and patients. Twenty-six of the 40 studies in healthy subjects showed peak response at 20 minutes, while nine showed it at 30 minutes Using the data acquired at 20 and 30 minutes, all 40 studies in healthy subjects showed normal results while none of 20 studies in patients was normal.

CONCLUSIONS

We conclude that the cortisol response to 1 microg ACTH stimulation was reproducible in both healthy subjects and patients with secondary adrenal insufficiency. In order to assess adrenal function more accurately with the 1 microg ACTH stimulation test, serum cortisol should be measured before and 20 and 30 minutes after ACTH injection.