Grading Hemoglobin (g/L) Clinical manifestations Mild 120-91(12-9.1g/dl) Mild symptoms Moderate 90-61(9-6.1g/dl) Panic and shortness of breath after physical exercise Severe 60-31(6-3.1g/dl) Panic and shortness of breath even at bed rest Extreme <30(less than 3.0g/dl) Often combined with anemic heart disease