Endocrine Abstracts (2004) 7 P168

Variability in GH assays undermines the value of consensus criteria for the diagnosis of adult GH deficiency and acromegaly

A Pokrajac-Simeunovic1, GE Wieringa2, AK Ellis3 & PJ Trainer1

1Department of Endocrinology, Christie Hospital NHS, Manchester, UK; 2Department of Biochemistry, Christie Hospital NHS, Manchester, UK; 3Department of Clinical Biochemistry, Royal Infirmary, Edinburgh, UK.

There is increasing reliance on published consensus criteria for clinical decision-making in states of GH excess and deficiency. NICE eligibility criteria for GH treatment include a peak GH response <9 mU/L during an ITT. To determine the adequacy of GH assay performance for diagnosing GH deficiency (GHD), we have assessed the variability in 101 UKNEQAS reported results from a single sample with a value close to 9.0 mU/L. For all laboratories (n=101) median GH was 11.1 mU/L (range: 6.6-13.9). 15% of laboratories reported GH <9 mU/L, so fulfilling NICE criteria for GH replacement. The most negatively biased method (n=11 labs, median 7.1 mU/L, range 6.6-7.7) classified all patients as GHD; the most positively biased (n=44, median 11.95 mU/L, 9.8-13.9) classified all patients as normal.

The current consensus for acromegaly states that the diagnosis is excluded by a nadir GH during an OGTT of <1 ug/L but with no stated mU/L equivalent. In the absence of an evidence base for an appropriate conversion factor, we have assessed diagnostic accuracy in 104 UKNEQAS reported results from a single sample using conversion factors of 2.6 and 3.0 (ug/l to mU/l). The 'all-laboratory' (n=104) median GH was 2.6 mU/L (range 1.04-3.5). Applying a conversion factor of 2.6, the most negatively biased method (n =10, median 0.69 ug/L, range 0.61-0.81) classified all the values as normal, while the most positively biased (n= 42, median 1.08 ug/L, 0.9-1.23) classified 93% of values as consistent with acromegaly. Applying a conversion factor of 3.0, 11% labs of reported values were consistent with acromegaly, while 89% were normal.

In summary, variability in GH assays undermines the applicability of international consensus criteria to local practice. A consensus on GH assay performance, taking into account the availability of an international GH calibrant and recently introduced EU legislation, is urgently required.

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