Whether a red blood cell count of 5.66 is normal or not depends on the sex and age of the patient. In case of children, the value is normal. 1. Normal values for red blood cell count: adult male red blood cell count (4.0-5.5) × 10¹²/L, normal adult female (3.5-5.0) × 10¹²/L, and child red blood cell count (4.0-7.0) × 10¹²/L. Therefore, if this test result is a child, the value is normal; if it is an adult male, the value is slightly high; if it is an adult female, the If it is an adult male, the value is slightly high; if it is an adult female, the value is high. 2. There are two types of increased red blood cell counts: relative and absolute. Absolute increases are divided into primary and secondary erythrocytosis. Relative increase is common in diarrhea and other causes of blood concentration; primary erythrocytosis is common in true erythrocytosis, and secondary increase is seen in the highland life of the population, as well as chronic lung disease people. Therefore, based on the test results alone, it is not possible to determine whether it is normal or not, it is recommended to consult the hospital in time, and the professional doctor to determine the specific causes.