Thiopurine methyl-transferase activity and azathioprine metabolite concentrations do not predict clinical outcome in thiopurine-treated inflammatory bowel disease patients

BACKGROUND

Low thiopurine-methyl-transferase (TPMT) activity and high 6-thioguanine-nucleotide (6TGN) concentrations have been linked to therapeutic success in inflammatory bowel disease patients treated with thiopurines; however, this has not been implemented in clinical practice.

AIM

To identify a therapeutic threshold value for TPMT or 6TGN concentrations, and their capability to predict treatment safety and efficacy.

METHODS

Prospective multicentre study including steroid-resistant/dependent patients starting thiopurines. The TPMT activity was determined at inclusion (>5 U/mL required). Azathioprine metabolites [6TGN, 6-methyl-mercaptopurine ribonucleotides (6MMP), and 6TGN/6MMP and 6TGN/TPMT ratios] were periodically monitored during steroid tapering and after withdrawal for 6 months or until a new flare occurred.

RESULTS

A total of 113 patients were analysed (62% clinical response). Areas under the receiver operating characteristic (ROC) curve (AUC) relating clinical response and metabolite levels at 2, 4 and 6 months after steroid withdrawal were less than 0.7. The AUCs relating final response and initial TPMT activity or metabolite concentrations at 2, 4, 8 and 16 weeks after starting thiopurines were less than 0.7. No cut-off point with worthwhile sensitivity/specificity was found. Eight (7%) patients developed thiopurine-related toxicity that could not be linked to TPMT activity or 6TGN levels.

CONCLUSIONS

Our results do not support determination of TPMT activity or 6TGN concentrations to predict treatment outcome, and no useful serum metabolites threshold value to adjust the drug's dose was identified.

Helicobacter pylori "test-and-scope" strategy for dyspeptic patients. Is it useful and safe?

AIM

To evaluate outcome of test-and-scope strategy using 13C-urea breath test, Helicobacter pylori IgG serology, and CagA serology.

PATIENTS AND METHODS

A series of 100 dyspeptic patients were studied. Biopsies were obtained for histology and rapid urease test (gold standard). Serum samples were obtained for Helicobacter pylori IgG and CagA serology, and 13C-urea breath test was carried out.

RESULTS

If endoscopy had not been performed in Helicobacter pylori patients based on 13C-urea breath test, <45 years, without alarm symptoms, and without non-steroidal anti-inflammatory drug use, 15% of endoscopies would have been saved, and one gastric ulcer and two oesophagitis would have been missed. Based on Helicobacter pylori IgG serology, 21% of endoscopies would have been saved. Finally, if endoscopy had been performed only in CagA+ patients, 31% of endoscopies would have been saved, missing one gastric ulcer and two cases of oesophagitis.

CONCLUSIONS

In our geographical area, the test-and-scope strategy based on 13C-urea breath test or Helicobacter pylori IgG serology would have saved only 15-20% of endoscopies. Although some relevant pathology would have been missed, it is not of a malignant type. 13C-urea breath test is the preferred non-invasive method to be used in this strategy, while Helicobacter pylori IgG serology is of limited value due to its low accuracy. With the use of CagA serology a larger number of unnecessary endoscopic examinations can be avoided.

13C-urea breath test for the diagnosis of Helicobacter pylori infection: are basal samples necessary?

AIM

The 13C-urea breath test (13C-UBT) is one of the best methods for the diagnosis of Helicobacter pylori infection. Basal breath samples are usually obtained, in addition to those obtained after urea intake, as it has been suggested that basal values may oscillate among a population (e.g. depending on diet). However, the superiority of this strategy has not been sufficiently demonstrated. The elimination of basal samples in the 13C-UBT protocol would have the advantages of higher simplicity and speed.

METHODS

The 13C-UBT was performed in 714 consecutive patients. Mean age was 48 +/- 16 years, 49% were males, and in 48% of the patients previous H. pylori eradication therapy had been administered. Basal samples (13C-basal) and at 30 min after taking 100 mg of urea labelled with 13C (13C-post-urea) were obtained, delta over baseline (13C-DOB) being the algebraic difference between the ratio 13C/12C at these two points (which is the parameter usually given in studies, being considered positive when > 5%). A citric acid solution was used prior to urea intake.

RESULTS

The prevalence of H. pylori infection was 48%. Mean values of 13C-basal, 13C-post-urea, and 13C-DOB were, respectively, -19 +/- 2, 5.9 +/- 33, and 25 +/- 33. 13C-basal values oscillated between -25 and -14, being between -21 and -16 in 90% of the cases. Linear correlation coefficient for 13C-post-urea and 13C-DOB was 0.999 (determination coefficient, 0.998; P< 0.0001). The area under the receiver operating characteristic (ROC) curve for the diagnosis of infection when only 13C-post-urea was used (taking 13C-DOB >5% as the 'gold standard') was 0.997. Best results were obtained with 13C-post-urea cut-off point set at -13, with sensitivity of 97.4% (95% CI, 95-99%), specificity of 99.5% (98-100%), and positive likelihood ratio of 180. The concordance kappa value for both tests (13C-post-urea and 13C-DOB) using the aforementioned cut-off point was 0.97.

CONCLUSION

When performing the 13C-urea breath test it is sufficient to obtain samples 30 min after urea intake. Basal breath samples would not be necessary, which further simplifies this diagnostic method.

Value of quantitative serology for confirmation of Helicobacter pylori eradication: an 18-month follow-up study

In this study several therapies were administered to 124 H. pylori-positive patients and IgG antibody titers were measured by ELISA at months 0, 2, 3, 6, 12, and 18 months. Serum titers of IgG antibody progressively decreased after H. pylori eradication; at 3 months, the area under the receiver operating characteristic curve for the decrease of IgG antibody titers for confirming H. pylori eradication was 0.99, with 100% sensitivity and 99% specificity (when the cutoff point was set at 3 U/mL). We conclude that a decrease in serum titers of IgG antibody to H. pylori relatively early after completion of therapy (1 month after ranitidine or bismuth therapy is completed and 2.5 months after antibiotic therapy is completed) can be used as a noninvasive, simple, and inexpensive method to confirm H. pylori eradication.

["Rapid" serology for the diagnosis of Helicobacter pylori infection. Evaluation of its accuracy compared with a gold-standard and its concordance with "classic" serology]

AIM

To prospectively evaluate the validity of a rapid office-based diagnostic serological test (using capillary blood) in our population, taking as reference a combination of standard diagnostic methods, as well as to compare the results of this technique with those of "classic" serological tests (using venous blood).

PATIENTS AND METHODS

We prospectively studied 39 consecutive patients with symptoms of the upper digestive tract who had undergone oral gastroscopy. Gastric biopsies were taken for histology and rapid urease testing, and a 13C-urea breath test was performed. An enzyme-linked immunoassay that detects IgG antibodies against Helicobacter pylori was used as a "classic" serological test and the commercial kit FlexPack HP was used as a "rapid" serological test. The endoscopist, the pathologist and those responsible for reading the rapid urease test, the 13C-urea breath test and both serological tests did not know the results of the other diagnostic methods. Patients were considered H. pylori positive when at least two of the three validated tests (rapid urease test, histology, and 13C-urea breath test) revealed infection and were considered free of infection when all tests were negative.

RESULTS

Thirty-nine patients were studied. Thirty-eight per cent were male (mean age 48 +/- 15 years). The prevalence of H. pylori infection detected by the gold standard was 69.2%. The sensitivity and specificity of the "classic" serological test was 96% 95% (CI: 79-99) and 91% (59-100). "Rapid" serological testing was positive in nine patients, negative in 28 and indeterminate in two. A single digital puncture was sufficient in 80% of the patients, 15% needed two and 5% needed three. Most patients (77%) had no preference for either type of serological test while 20.5% preferred digital puncture and 2.5% venous puncture. The sensitivity, specificity, positive predictive value and negative predictive value were 31% (16-50), 91% (59-100), 89% (52-100) and 36% (19-56) respectively. Sensitivity was unaffected by age but specificity was lower in patients older than 40 years (89% vs. 100%; McNemar's test: 8; p < 0.01). Kappa's coefficient between the "classic" and the "rapid" serological tests was 0.16 (SE 0.1) and McNemar's test was 12.2 (p < 0.001), which indicates that the prevalence of infection diagnosed by both methods was not homogeneous.

CONCLUSION

The "rapid" office-based serological test used in our study is of insufficient diagnostic accuracy to be used in clinical practice to identify H. pylori infection.