Is red cell sorbitol content a good marker of glycemic control in diabetic patients?

Red cell sorbitol (RCS) concentration and some metabolic parameters were evaluated in 62 diabetic patients. 42 normal subjects were studied as controls. RCS levels were 66.1 +/- 2.0 nmol/gHb in diabetic patients and 41.8 +/- 2.0 nmol/gHb in controls (p less than 0.001). RCS levels were positively correlated with all metabolic parameters evaluated in diabetic patients and in controls. To evaluate RCS distribution, diabetic subjects were subdivided in 3 groups according to fasting plasma glucose (FPG) (less than or equal to 150; 151-200; greater than 200 mg/dl) and glycosylated hemoglobin (GHb) levels (less than or equal to 8; 8.1-10; greater than 10%). 31 patients with FPG less than or equal to 150 mg/dl, all except 7, had RCS levels in the normal range. These 7 patients however had GHb levels greater than 10%. 18 patients with FPG between 151-200 mg/dl had RCS levels in the normal range. Of 13 patients with FPG greater than 200 mg/dl all, except 3, had RCS levels above the normal range. These 3 patients had GHb levels greater than 10%. 45 patients with GHb less than or equal to 10% had RCS values in the normal range. 17 patients with GHb levels greater than 10%, had RCS levels over the normal range. Our data show that RCS levels seem to be related more strictly with GHb. RCS levels increase significantly only in patients with bad metabolic control. Even if RCS levels seem to be a medium-term index of metabolic "equilibrium" they cannot be useful in the routine monitoring of metabolic control in diabetic patients.