Valores de corte para índices de insulinorresistencia, insulinosensibilidad e insulinosecreción derivados de la fórmula HOMA y del programa HOMA2: Interpretación de los datos

RESUMEN

Se suele evaluar Insulinorresistencia (IR) mediante "Insulina e índice HOMA-IR" pero hay escasa publicación sobre valores de referencia y/o corte para evaluar IR en el Síndrome Metabólico. Un mismo valor de HOMA-IR puede provenir de diversos pares de glucosa/insulina; esto aporta información insuficiente si no se consigna el % de β-secreción (%B) y el % de Sensibilidad (%S). Objetivos: 1º) Calcular (para Insulina medida por MEIA) los valores de corte a informar para HOMA-IR, %B y %S, obtenidos a partir de la fórmula HOMA. 2º) ídem, para esos índices obtenidos del programa HOMA2. 3º) Dadas las múltiples combinaciones de datos que pueden confluir en un mismo HOMA-IR o un mismo %B, interpretarlos en una gráfica para facilitar su evaluación. Valor de corte se realizaron 208 TTOG obteniéndose para HOMA-fórmula y HOMA2 los siguientes HOMA-IR, 2.64, HOMA2, 1.67; %S 37.8% y HOMA2-%S 59.9%. %B 67.6% y HOMA2-%B 73.0%; Interpretación de datos si en un gráfico de insulina vs. glucosa se unen todos los puntos correspondientes a un mismo HOMA-IR se obtiene una curva de iso-HOMA, lo mismo para la recta de iso-%B. Repitiendo la operación con varios valores de HOMA-IR y de %B se obtiene una gráfica, en la cual los iso-HOMA e iso-%B de corte delimitan 4 zonas, y la ubicación de los datos de un paciente en c/u de ellas tiene significados diferentes, que se interpretan en este trabajo. Conclusión: debe informarse siempre HOMA-IR, %S, y %B como indicador del status β-secretor.

ABSTRACT

BACKGROUND: insulin resistance status is frequently evaluated through the HOMA-IR index, but there still is a widespread missunderstanding about its interpretation. β-cell status is evaluated through the %B (β-secretion). Still, there are very few papers regarding cut-off values for HOMA-IR and its associated indexes that arise from the original HOMA formula. Indeed, the need of evaluation IR as a main component of the Metabolic Syndrome as defined by the WHO committee (1999), led us to try to calculate the cut-off value for HOMA-IR in case Insulin is measured by MEIA (Abbott Laboratories). A single HOMA-IR value (as well as %S, %-Sensitivity) may come from different glucose-insulin pairs, so that in itself it provides little information, specially regarding β-secretory status. That lack of information must be assessed through %-B, which also comes from different combinations of glucose-insulin values. OBJECTIVE: The aims of this study are 1º) To calculate the cut-off values for HOMA-IR, %-S, %-B, to be reported along with Insulin to the physicians, as obtained by HOMA-formula. 2º) To calculate the cut-off values for HOMA2-IR, %-B, %-S as provided by the HOMA2 Calculator. 3º) Considering that each value of HOMA or %-B may come from multiple combinations of glucose-Insulin pairs, to design a graphic in which a patients status migth be evaluated. METHODS AND RESULTS: 208 OGTT were performed according to WHO 1999 recomendations, 110 patientes and 98 controls. Statistics were calculated by using G. Reaven's criteria about upper and lower quartile among people under 30kg/m² BMI. Data calculated were upper quartile for HOMA-IR 2.64; for HOMA2 1.67; lower quartile for %S 37.8%, HOMA2-%S 59.9%; lower quartile for %B 67.6%, HOMA2-%B 73.0%. Study and interpretation of the data we can calculate the different pairs of data that converge onto a same value of HOMA-IR (table3); if we then plot on a graphic Insulin vs. Glucose those different points, we could see a curve ranging from "low glucose-high insulin" points to "high glucose-low insulin" others (Fig. 1). We can draw a curve for each HOMA-IR value, but for the evaluation it is enough if we take the cut-off value and some lower and higher ones (Fig. 4). The same can be done for each data of %-B (table 4); in this case, we obtain a straigth line with a positive slope; the highest the %B, the highest the slope. Just like before, we can plot the cut-off value for %B, and some lower and higher (Fig.5). If we plot all this curves in a unique Insulin vs. Glucose graphic (Fig. 6), then we can see that the intersection of both cut-off lines leaves on the graphic four zones (beyond the uncertainty zones undermentioned), (Fig. 7, 8). The position of the pair of data of a patient on the plot could allow to predict about his insulin-sensitivity and β-secretory status, in spite of β-cell pulsatility. CONCLUSIONS: Cut-off data were calculated for MEIA-Insulin HOMA-IR (2.64), %B(67.6) y %S (37.8). For HOMA2-Calculator HOMA-2 1.67; HOMA2-%B 73.0%; HOMA2-%S 59.9%. Given the limited information provided by HOMA-IR alone e suggest that patient´s reports for the physicians include HOMA-IR as well as %S, in order to evaluate the β-cell status and try to predict β-claudication as early as possible before it takes place. Nonetheless, in the long-time-evaluation of a patient, the method of Insulin dosage should be, if possible, the same one.