Since even very small MTCs tend to metastasise  and prognosis depends on early diagnosis and treatment [6, 28, 29], which consists of thyroidectomy and lymphadenectomy , early detection and management play an important role despite the low prevalence of MTC. The prospects for cure are excellent after surgery if treatment is instituted at an early stage, i.e. before MTC has metastasised. A 10-year survival rate of 97.7% has been reported . Because of the high sensitivity and specificity of serum hCT measurement by immunoassay technology using two monoclonal antibodies routine hCT measurement has been suggested for assesment of patients with thyroid nodular disease by major authorities in Europe [2, 20, 32, 33] and the United States [34, 35]. Yet it is not rountinely performed in most cases. In a survey of Bennebaek et al. the serum hCT measurement was only used in 43% of all cases with nodular thyroid disease . However the routine use of serum hCT screening in patients with nodular thyroid disease is still under debate . There are also several authors, who do not recommend the routine use because of the hight prevelance of thyroid nodules and the rarity of MTC. Routine hCT measurement has no general acceptance in the US . Therefore the expert panel of the ATA (American Thyroid Association) could not recommend either for or against the routine measurement of serum calcitonin in 2009 (Recommendation rating: I) . Despite the previous AACE-AME guidelines did not endorse the routine measurement of hCT the revised 2010 guidelines favors, but does not recommend, routine hCT testing: “measurement of basal serum calcitonin level may be useful in the initial evaluation of thyroid nodules” .
The European Thyroid Association (ETA) and the German Society of Endocrinology (DGE) recommend the routine hCT screnning in patients with nodular thyroid disease [14, 15, 30].
Patients with clinically apparent MTC usually have serum hCT levels that are 10 to 100 times higher than normal. Markedly elevated hCT levels are thus indicative of MTC. At postoperative follow-up, such levels may suggest a recurrence or untreated metastases . Patients with mildly or moderately elevated hCT levels (not exceeding 100 pg/ml) are difficult to evaluate, especially since the literature reports a number of factors that can influence serum calcitonin concentrations [3, 8, 15, 18]. Hypercalcitoninaemia can occur with a broad spectrum of conditions. An elevation of calcitonin levels can be found not only in patients with MTC but also in patients with C-cell hyperplasia (CCH), which is difficult to differentiate and may precede MTC. In addition, up to 22% of patients with renal failure present with markedly elevated serum hCT concentrations . In the literature, moderate elevations in serum hCT levels (not exceeding 100 pg/ml) were also reported in patients receiving proton pump inhibitor (PPI) therapy [16, 17, 40] as well as in patients with Hashimoto’s thyroiditis [18, 19].
Likewise, hypercalciuria , paraneoplastic syndromes , and chronic alcoholism  were found to induce an increase in hCT levels. By contrast, there is no evidence to support earlier research suggesting that elevated hCT levels are caused by medicines containing calcitonin or salmon calcitonin [15, 26] or elevated procalcitonin levels associated with bacterial infections , which were found by modern highly specific and sensitive assays without cross-reactivities to be largely insensitive to the aforementioned influences.
The interpretation of mildly or moderately elevated serum hCT concentrations always requires that the risk of surgery for a benign condition be weighed against the risk of missing an MTC. For this reason, the diagnostic role of serum hCT concentrations is a matter of debate .
When the test kit (Calcitonin IRMA magnum) was used in this study to compare immediate and delayed analyses of hCT levels, there were no significant differences in the results when low levels within normal limits were measured. A delayed analysis of blood samples with hCT levels that were primarily elevated but still within normal limits led to a few lower values after two hours at room temperature. This suggests that false low results can indeed be produced in the case of elevated hCT concentrations and a delayed analysis. Accordingly, valid results can only be obtained if the processing steps and times specified by the manufacturer of the assay are strictly observed .
The present results confirm the finding that men have significantly higher serum hCT concentrations than women. Saller et al. and Vierhapper et al., too, reported gender-specific differences and measured higher basal serum hCT concentrations in men [2, 12]. According to the manufacturer of the immunoradiometric assay used in this study, normal calcitonin levels in the serum of healthy persons range from 0 pg/ml to 15 pg/ml in men and from 0 pg/ml to 10 pg/ml in women . Elevated serum hCT concentrations in women must receive particular attention since a medullary thyroid carcinoma is the underlying cause in approximately 80% of the cases . By contrast, moderately elevated serum hCT concentrations in men are the result of C-cell hyperplasia in up to 80% of the cases .
The maximum difference between mean levels was 3.304 pg/ml (maximum standard deviation: 9.4468). This is mainly attributable to the considerable number of outliers observed for Group 4 (healthy thyroid and PPI therapy). When a statistical analysis of the medians was performed in order to minimize the influence of outliers, the maximum between-group difference was 1.98 pg/ml. This difference was slightly above the functional assay sensitivity (approximately 1.5 pg/ml) specified by the manufacturer.
Unlike Schütz et al. and Karanikas et al., we did not observe an elevation of serum hCT concentrations in patients with Hashimoto’s thyroiditis [18, 19]. The mean and median concentrations of patients with Hashimoto’s thyroiditis were not significantly different from those obtained for the control group. Compared with the other groups, patients with Hashimoto’s thyroiditis had even the lowest mean and median concentrations. The findings presented here show that the serum hCT concentrations in our patient population were uninfluenced by the presence or absence of Hashimoto’s thyroiditis. As a result, elevated serum hCT levels were not caused by Hashimoto’s thyroiditis and generally require special diagnostic attention.
Likewise, neither the mean nor the median serum hCT concentrations of patients with nodular goitre were significantly different from those of the control group, regardless of whether the patients received or did not receive PPI therapy. For this reason, elevated serum hCT levels were not attributable to nodular goitre and require further diagnostic evaluation.
The literature reports mild or moderate increases in serum hCT concentrations after short periods of treatment with PPIs [16, 17]. There were considerable differences in these increases. Vitale et al. found, for example, that gastrin responsiveness to omeprazole had great variability . This can be explained by the effects of gastrin. In the present study, there were no significant differences between patients who regularly took PPIs and control subjects with a normal thyroid who did not take PPIs. The regular use of PPIs may lead to a habituation effect so that calcitonin levels are no longer elevated in response to gastrin levels. The regular use of PPIs is thus not associated with an increase in serum hCT concentrations irrespective of whether patients have a normal thyroid or present with nodular goitre. It is interesting to note, however, that patients with a healthy thyroid and PPI therapy showed an increased number of outliers. Nevertheless, an elevation of serum hCT concentrations is not necessarily attributable to the regular use of PPIs.
The present study emphasises the low susceptibility to errors of calcitonin screening. Contrary to some authors the study suggests that an elevation of hCT levels cannot be explained by conditions such as Hashimoto’s thyroiditis, nodular goitre or PPI therapy [15, 16, 18].
When patients have hCT levels higher than the gender-specific upper limits, the underlying cause must be thoroughly investigated. Technical problems must be ruled out. Where appropriate, a different assay should be used to perform a second measurement in order to confirm the presence of hypercalcitoninaemia . An intravenous calcium stimulating test or a pentagastrin stimulation test should be performed in thoses cases . A marked increase in serum hCT levels to ten times the normal level after pentagastrin or calcium stimulation is clear evidence for MTC and is an indication for thyroidectomy [3, 15, 30]. This approach allows the vast majority of medullary thyroid carcinomas to be detected and treated in time. Although this implies that a notable number of patients with C-cell hyperplasia, especially male patients, are likely to undergo surgery, the poor prognosis of metastatic MTC justifies this approach.
The results of laboratory tests might be affected by the molecular heterogeneity of calcitonin. Therefore serum calcitonin concentration can vary because different assays use antisera that recognize different epitopes of the calcitonin molecule. At present two-site immunoassays are commonly used. These tests combine monoclonal antibodies against regions, which are unique to the mature form of the calcitonin molecule. A radioisotopic (IRMA) or luminescent (ILMA) labeling is currently regarded as the most accurate [3, 43]. In this study the IRMA is used. So there might be limitations in transfering the results presented here to results gathered by other assays and labelings.
The strength of the results presented here is limited by the number of subjects. Furthermore the men to women ratio is 5:1 in this study whilst worldwide the prevalence of thyroid diseases in particular Hashimoto’s thyroiditis is higher in the female then in the male sex. Therefore further studies are required to confirm the findings.