Biochemical definitions of disease activity in acromegaly

Quantification of day-to-day variability in growth hormone levels in acromegaly

Growth hormone (GH) measurements are routinely used for important treatment decisions in patients with acromegaly, yet their reliability is affected by numerous factors including assay precision and variability, sampling intensity, and hormone pulsatility. The day-to-day variation in GH in acromegaly has not been studied. This study quantified the magnitude of day-to-day GH variability in patients with acromegaly by performing an analysis of previously obtained plasma GH profiles. The analysis was performed at the Michigan Clinical Research Unit at the University of Michigan. A total of nine 48 h Q10 min GH profiles obtained in nine patients with active acromegaly were examined. The study was planned after data collection and analysis was conducted using Altman-Bland methods. Day 1 vs. Day 2 values were examined. 95% confidence intervals of the D2 vs. D1 ratios were calculated on all individual subject data as well as on a single 0800 h GH sample and composite mean data for 2-, 5-, 9-, and 24-h sampling protocols. Confidence interval range was 0.66-1.50 for the 0800 h sample and was similar for all sampling protocols except somewhat more narrow for the 24-h sampling (0.75-1.32). Daily variations in GH levels introduce an additional confounding element when using a single GH level or even daily GH curves to assess a patient's GH milieu. It may have an impact on result interpretation and subsequent treatment decisions especially when GH results are considered borderline.

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

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.