Verificación del punto de corte de la prueba cualitativa para la determinación de sangre oculta y comparación de resultados con una determinación automatizada de hemoglobina en heces
Fecha
2020-12-15
Tipo
tesis
Autores
Montoya Madriz, Stephanie
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Resumen
El cáncer colorrectal es una enfermedad de alta incidencia en el mundo y Costa Rica no es la excepción, por lo que se han implementado programadas de tamizaje para poblaciones de riesgo. Se busca detectar las pérdidas imperceptibles de sangre en heces por medio de pruebas químicas o inmunológicas. El cáncer colorrectal en Costa Rica representa la cuarta causa de cáncer en hombres y sexta en mujeres, siendo la quinta causa de mortalidad en hombres, y tercera en mujeres. Los síntomas son inespecíficos y las posibilidades y tipo de tratamiento depende de la etapa en la cual se descubra el padecimiento.
Existen diferentes tipos de técnicas para la detección de sangre oculta, la clásica es el guayaco que se basa en un método químico y que ha caído en desuso debido a sus múltiples interferencias; actualmente se usan técnicas inmunológicas, puesto que son más específicas y sensibles, y no presentan interferencias. En el presente trabajo se verificó el punto de corte de la prueba inmunocromatográfica que está cercano a la concentración de 24,62 ng/mL y se determinó que la zona gris se encuentra entre la concentración de 15,15 ng/mL y la de 35,04 ng/mL. Para la comparación de ambos métodos se obtuvo una sensibilidad del 62 %, una especificidad del 97 %, una tasa de falsos positivos de 3 %, la tasa de falsos negativos en comparación con el método cuantitativo es de 38 % y el denominado valor predictivo positivo es de un 53 %. Mientras que el valor predictivo negativo o la probabilidad de verdaderos negativos es de un 98 %, lo cual quiere decir que de detectados como negativos un 98 % realmente carecen de lesiones que preceden al cáncer de colon. El porcentaje de acuerdo observado entre las pruebas es de 95,6 %. En conclusión, el comportamiento de la prueba es bastante aceptable para su uso como tamizaje, la escogencia dependerá de las necesidades del programa, así como del recurso económico disponible.
Colorectal cancer is a disease with a high incidence in the world and Costa Rica is no exception. For this reason, screening programs for at-risk populations have been implemented, in order to detect imperceptible losses of blood in the stool by means of chemical or immunological tests. In Costa Rica, this cancer represents the fourth cause of cancer in men and the sixth in women, being the fifth cause of mortality in men, and the third in women. The symptoms are nonspecific and the possibilities and type of treatment depend on the stage at which the condition is discovered. There are different types of techniques for detecting occult blood, the guaiac test is the classic one, although this chemical-based method has fallen into disuse due to its multiple interferences; furthermore, immunological techniques are currently used, since they are more specific and sensitive, and do not present interferences. In this work, the cut-off point of the immunochromatographic test was verified, which is close to the concentration of 24,62 ng/mL and the gray area between the concentration of 15,15 ng/mL and that of 35,04 ng/mL. The comparison of both methods gave a sensitivity of 62 %, a specificity of 97 %, a false positive rate of 3 %, the false negative rate compared to the quantitative method is 38% and the so-called positive predictive value is 53%. Also, the negative predictive value or the probability of true negatives is 98 %, which means that 98 % of those detected as negative actually lack lesions that precede colon cancer. Finally, the percentage of agreement observed between the tests is 95,6%. In conclusion, the behavior of the test is quite acceptable for its use as a screening, the choice will depend on the needs of the program, as well as the economic resource available.
Colorectal cancer is a disease with a high incidence in the world and Costa Rica is no exception. For this reason, screening programs for at-risk populations have been implemented, in order to detect imperceptible losses of blood in the stool by means of chemical or immunological tests. In Costa Rica, this cancer represents the fourth cause of cancer in men and the sixth in women, being the fifth cause of mortality in men, and the third in women. The symptoms are nonspecific and the possibilities and type of treatment depend on the stage at which the condition is discovered. There are different types of techniques for detecting occult blood, the guaiac test is the classic one, although this chemical-based method has fallen into disuse due to its multiple interferences; furthermore, immunological techniques are currently used, since they are more specific and sensitive, and do not present interferences. In this work, the cut-off point of the immunochromatographic test was verified, which is close to the concentration of 24,62 ng/mL and the gray area between the concentration of 15,15 ng/mL and that of 35,04 ng/mL. The comparison of both methods gave a sensitivity of 62 %, a specificity of 97 %, a false positive rate of 3 %, the false negative rate compared to the quantitative method is 38% and the so-called positive predictive value is 53%. Also, the negative predictive value or the probability of true negatives is 98 %, which means that 98 % of those detected as negative actually lack lesions that precede colon cancer. Finally, the percentage of agreement observed between the tests is 95,6%. In conclusion, the behavior of the test is quite acceptable for its use as a screening, the choice will depend on the needs of the program, as well as the economic resource available.
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Palabras clave
sangre, oculta, heces, guayaco, cuantitativo, cualitativo, cáncer, colorrectal