Although the specificity and positive predictive value appear promising, they are derived from very small numbers (only two positive tests). More important is the very low sensitivity and negative predictive value, both of which are based on larger numbers. Analysis of more than 100 patient samples might confirm that the positive predictive value is high. However, it would be hard to justify clinical use if the test were positive in less than 15 percent of cases, especially since many patients with indeterminate bronchoscopy results will go on to thoracotomy anyway. A test with a high negative predictive value would be much more useful in this clinical setting.
There are a number of potential explanations for the difference in our findings. First, we were analyzing BAL rather than bronchial washings, and some might expect the IgA to be much less in the distal airways. Although the concentration of IgG increases as one goes from the upper to the lower respiratory tract, IgA is still present in high concentrations in BAL fluid. In fact, of the В cells found in BAL, most are IgA secreting; and the IgA/albumin ratio, unlike the IgC/albumin ratio, is much higher in BAL than in serum. These findings suggest that a measurable amount of slgA is produced locally in the lower respiratory tract. Second, we were making measurements only in patients without endoscopically visible tumor, whereas most of the other studies examined primarily patients with endoscopically visible tumors. Third, the majority (six of eight) of our cancer patients were found to have advanced stage (stage III or greater) disease and there is evidence that humoral immune response and IgA levels are diminished in lung cancers of advanced stage. The fact that the only cancer patient in this study with marked elevation of slgA had stage III disease argues against this explanation. Fourth, BAL may have been collected from a subseg- ment that did not harbor the cancer. In this regard, localization was carried out to the best of our ability using fluoroscopic guidance. We reasoned that if more elaborate measures would be required, then the likelihood of widespread clinical use would be minimal. kamagra oral jelly 100mg
Regardless of the explanation, we conclude that slgA measurements on BAL supernatants are not likely to be clinically useful in predicting the presence of cancer. Future studies using a study design similar to ours examining bronchial washings (slgA) may produce different results. Such studies would need to be done before the interesting retrospective observations regarding increased slgA in lung cancer could become clinically significant.