Assessment of the magnitude of growth hormone hypersecretion in active acromegaly: reliability of different sampling models

Abstract

Context: The pulsatility of GH secretion in acromegaly poses difficulty in ascertaining true daily GH milieu in patients with this disease. Intensive GH sampling [every 10-20 (Q10-20) min for 24 h] is not practical in clinical practice.

Objective: Our objective was to ascertain reliability of abbreviated sampling protocols to reflect true 24-h mean GH concentrations in patients with acromegaly.

Design: An analysis of previously obtained plasma GH profiles was performed.

Setting: The analysis was performed at the General Clinical Research Center at the University of Michigan.

Patients: A total of 115 GH profiles obtained in 94 patients with active acromegaly were examined.

Intervention: Frequent blood sampling, i.e. Q10-20 min for 24 h, was performed.

Main outcome measures: Concordance of 24-h mean GH concentrations derived from Q10- to 20-min samplings with abbreviated GH sampling schedules was performed. The study was planned after data collection.

Results: All abbreviated schedules of GH sampling correlated well with the true 24-h plasma GH means (i.e. Q10- to 20-min sampling) (R = 0.93-0.98; P < 0.0001 for all). In the GH range more than 20 microg/liter, only 5 and 9-h means had R values more than 0.9. Single GH concentrations less than 1 microg/liter had a positive predictive value of only 0.29, and those with less than 2.5 microg/liter had a positive predictive value of 0.67 vs. their corresponding 24-h mean GH values of the same magnitude.

Conclusions: The intensity of GH sampling in patients with acromegaly may vary depending on the nature of the required information. Investigators and clinicians should be aware of the limitations of the abbreviated GH sampling protocols in acromegaly.

Figure 1

Correlation between 24-h GH means using Q10 and Q20-min protocols. A total of 103 Q10-min GH series was analyzed using every or every other GH sample.

Figure 2

Correlations between 24-h GH mean and single 0800-h GH value (A), 2-h GH mean from three samples (B), 5-h GH mean from six samples (C), and 9-h GH mean from 10 samples (D).

Figure 3

Sample GH mean using a single 0800-h value or 2-, 5-, 9-, and 24-h means. Whiskers denote se.

Figure 4

Concordance between a single 0800-h GH value, and 2-, 5-, and 9-h GH means, and their appropriate 24-h GH means. Whiskers denote 95% confidence intervals in the intervals of proportions.

Figure 5

Altman-Bland analysis of comparison between the Q20- and Q10-min 24-h mean GH concentrations.

Figure 6

Summary of the Altman-Bland analysis of comparison between different sampling paradigms and “true” 24-h mean GH derived from Q20 or Q10-min samplings. Whiskers denote 95% confidence intervals.