Hemoglobina glucosilada

Sinónimo: hemoglobina glucosilada

¿Qué es una prueba de HbA1c?¹

Glycated haemoglobin (HbA1c) laboratory tests are used to diagnose diabetes mellitus and to monitor diabetic control. For further information regarding HbA1c monitoring and targets, see the separate Manejo de la diabetes tipo 1 y Tratamiento y manejo de la diabetes tipo 2 artículos.

Hemoglobina A1 y hemoglobina A1c

La cromatografía de la sangre normal de un adulto se divide en dos partes:

• HbA (HbA0) 92-94%.

• HbA1 (6-8%) where the B chain has an additional glucose group. HbA1 itself consists of three different glycations, the HbA1c subgroup being the most useful.

High-performance liquid chromatography, immunoassay-based assessments, and enzymatic assays can all be used to measure HbA1c levels.²

The glycation of haemoglobin occurs at a variable (non-linear) rate during the lifespan of the red blood cell (RBC), which is normally 120 days. The relative proportion of glycated haemoglobin at any one time depends on the mean glucose level over the previous 120 days.³

Normal levels (laboratory normal 'range') will differ depending on the method used.

El HbA1c suele ser un indicador confiable del control diabético, excepto en las siguientes circunstancias:²

• Situations where the average RBC lifespan is significantly less than 120 days will usually give rise to low HbA1c results because 50% of glycation occurs in days 90-120. Common causes include:³

  • Aumento del recambio de glóbulos rojos: pérdida de sangre, hemólisis, hemoglobinopatías y trastornos de los glóbulos rojos, enfermedad mielodisplásica.

  • Interference with the test: persistent fetal haemoglobin and haemoglobin variants, carbamylated haemoglobin (uraemic patients).

• In patients who fluctuate between very high and very low levels, HbA1c readings can be misleading (the clinician should compare with extra information obtained from home capillary blood glucose tests).

Rangos normales de HbA1c

HbA1c results in the UK have been standardised to the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) allowing global comparison of results, with the normal non-diabetic range of IFCC-HbA1c being 20-42 mmol/mol.

Otros puntos importantes a considerar

• Cualquier objetivo de HbA1c para el manejo de una persona con diabetes debe ser individualizado y acordado con el paciente (considerando comorbilidades, esperanza de vida, frecuencia de hipoglucemias, etc.).

• Do not test more frequently than every three months.

Diagnóstico de la diabetes

• Diabetes is usually diagnosed by an HbA1c of 48 mmol/mol or more. If the use of HbA1c is inappropriate (eg, people with end-stage chronic kidney disease), type 2 diabetes is diagnosed by a fasting plasma glucose level of 7.0 mmol/L or greater.

• In an asymptomatic person, the diagnosis of diabetes should not be based on a single abnormal HbA1c level; at least one additional abnormal HbA1c level is essential. If the second test results are normal, it is prudent to arrange regular repeat HbA1c blood tests.

• In a symptomatic person, diabetes can be diagnosed with more confidence on the basis of a single abnormal HbA1c level (although a second test may be prudent).

• Hyperglycaemia in people with an acute infection, trauma, circulatory or other stress may be transitory and should not be regarded as diagnostic of diabetes.

• HbA1c levels between 43 and 47 are diagnostic of non-diabetic hyperglycaemia or pre-diabetes. Patients with pre-diabetes should have annual HbA1c tests.⁴

Situaciones en las que la HbA1c no es adecuada para el diagnóstico de diabetes incluyen:⁵

• Niños y jóvenes.

• Pregnancy or women within two months post-partum.

• Pacientes con síntomas de diabetes por menos de dos meses.

• Pacientes con alto riesgo de diabetes que están gravemente enfermos.

• Patients taking medication that may cause hyperglycaemia - eg, steroids, antipsychotics.

• Pacientes con daño pancreático agudo, incluyendo cirugía pancreática.

• Patients with end-stage renal failure.

Monitoreo de HbA1c para la diabetes^{6 7}

Para las personas con diabetes tipo 1, el Instituto Nacional para la Salud y la Excelencia en el Cuidado (NICE) recomienda:

• Niveles de HbA1c cada tres a seis meses en adultos con diabetes tipo 1.

• Consider measuring HbA1c levels more often in adults with type 1 diabetes if their blood glucose control is suspected to be changing rapidly.

Para adultos con diabetes tipo 2, NICE recomienda:

• Intervalos de tres a seis meses (adaptados a las necesidades individuales), hasta que el HbA1c sea estable con una terapia sin cambios.

• Intervalos de seis meses una vez que el nivel de HbA1c y la terapia para reducir la glucosa en sangre estén estables.

If HbA1c monitoring is invalid because of disturbed erythrocyte turnover or abnormal haemoglobin type, trends in blood glucose control should be estimated using one of the following:⁸

• Estimación de fructosamina.

• Perfiles de glucosa en sangre controlados por calidad.

• Estimación total de hemoglobina glucosilada (si hay hemoglobinas anormales).

Fructosamina

Fructosamine is the glycated fraction of all plasma proteins (predominantly albumin) but considered less accurate because of the numerous factors affecting the half-lives of the many components. It generally reflects average glucose in the previous two weeks. If available, it may be useful in situations where there is reduced red cell survival time.⁹