by Oscar Fay

It could be said that from the 70s a new era began in the concept of the tasks of the clinical analysis laboratory, since a large number of instruments began to be commercialized, especially in clinical chemistry (glucose, urea, cholesterol, etc) that allowed to develop and use a greater number of tests for diagnostic use.

This proliferation of commercial teams accompanied by a change in the "medical culture."

From then on it became almost impossible that a diagnosis, follow-up, treatment and prognosis of the disease were not accompanied by laboratory tests that permanently increased in number and dispersion.

So that today, with almost two decades of experience, it could be said that the analytical universe in general poses a decision problem when faced with the real utility of each test and the economic and technical possibility of its performance.

In the operating conditions of clinical analysis laboratories and Latin America, and especially in developing countries, there is access to information on the very frontier of knowledge, and on the other an economic reality that overwhelms and makes it impossible to grow harmoniously or access to the so-called cutting edge technology.

In the times that lie ahead, this gap will surely grow deeper, and it is time to reflect on how to adapt the true needs of the exams to this changing and accelerated reality of a whole technology that the developed world has turned to the healthcare environment.

Only if this cultural change is an authentic, leading and permanent change in attitude, will it be possible to take advantage of this circumstance for really positive purposes. The change must be made with the active participation of all sectors involved in this development phenomenon.

There, the biochemist should know in depth "what is happening in his entire professional world", and in what way to what extent his reality requires selectively from this massive technological offer.

The integration, the participation of the biochemist in the health teams, will allow you not only to know the real analytical demand (when and in what case a certain pathology must be studied with a defined laboratory) but also in what way the chosen exam (s) have a meaning or a correlation with clinical, pathological anatomy, or imaging.

This interdisciplinary attitude will not only grant an absolutely utilitarian and practical role to your activity, but it will surely give you a correct and adequate dimension of what the laboratory can specifically contribute.

In the practical field, what has given excellent results in solving this problem have been the so-called "tracing tests", which allow, in the event of being normal or not significant, to exclude a large group of pathologies, while for those whose results are doubtful or abnormal, give the possibility of continuing to advance in complexity to the extent that it is justified and required. What should be avoided is the inverse path, that of choosing a very specific or very particular test at the beginning or at the beginning of a study, since it has been shown that this, although it sometimes provides a highly significant result, in most cases. cases yield a negative result, which would allow to exclude or mask others, which, although of less significance, are at the moment more significant.

For this reason, the demand for analysis must be staggered, of increasing and summing complexity, directed or specific, all the more the greater the significance sought.

A relatively large number of laboratory tests is presented in this chapter, in order to show a more or less wide spectrum of the analytical possibilities of the medium. However, it is considered necessary to suggest that the use of a test or a group of tests be carried out with a criterion such as to avoid the overlap and duplication of costs and tasks, which in the end imply an accumulation of efforts that are not compensated by the costs. results. And what is even worse, they generate a state of frustration to disbelief by creating expectations that cannot be fulfilled beforehand.

Otro aspecto sobre el que se ha pretendido realizar un aporte, ha sido en el concepto de sensibilidad y especificidad de una prueba, condiciones que a menudo 50 suponen como innatas o garantizadas en cada una de ellas. Sin embargo, en este concepto no solo inf1uye la característica tecnica de la prueba misma, sino tambien la población sobre la cual se utiliza la prueba.

To find an adequate balance between both instances, it is essential to know the patient or the individuals on whom it is performed. A test to detect antibodies against trypanosome, human immunodeficiency virus or toxoplasm in an uninfected or general population is not the same as performing the same test when there are other associated conditions, such as tuberculosis, sexually transmitted diseases, autoimmune diseases or chronicles. The specificity is compromised when it is evaluated against coinfections or situations called comorbid.

Another aspect to consider is the evolutionary moment of the disease in question, especially in infections; The sensitivity of a test in an asymptomatic state of infection is not the same as in an active infection stage.

Commercial test components contain varying amounts and qualities of reagents, especially for the type of tests taken as example. This phenomenon has been noted much more with the use of monoclonal antibodies and antigens obtained by genetic engineering, which in general mimic or recall the same activity as the original protein, but which have been produced in bacteria, yeast or mammalian cells under conditions different from those in which they are synthesized by the infective microorganism itself, in a biologically active ecosystem under conditions of survival and competition different from those created artificially.

This phenomenon has been solved with the use of local or regional serum panels for reference values ​​or to evaluate the sensitivity and specificity of any test on which it is desired to know its clinical value.

Finding an appropriate "cut-off", or limit of significance, often balances sensitivity and specificity. However, there is always a specific "gray area" where this specific problem is often solved, performing a second test on the sample in question that is of lower sensitivity but of greater specificity; this is correct, but may cause only borderline or borderline results to be repeated, but clearly negative results are never checked. The solution of this instance is achieved when each laboratory or reagent manufacturer establishes the reproducibility of a negative value.

Each laboratory is expected to achieve an adequate number of tests for each test to establish its "confidence interval". This interval is affected by the number of tests performed, the prevalence of the disease in the population, and the size of the population.

To solve the factors considered, a great advance has been made with the development of regional reference laboratories, especially when these are integrated as a "laboratory network" and exchange results, experiences and reference panels.

Finally, another fact that frequently interacts in the use of certain techniques, substantially modifying their value or affecting the technical performance itself, is the presence in the material to be analyzed of drugs or their metabolites that alter not only the significance of the results but also their numerical value.

Those laboratory tests on which this effect most frequently occurs have been pointed out, trying to alert about the importance of an anamnesis prior to its requirement. and therefore consider the conditions of the patient in whom a clinical analysis is performed.