My son age 6 years has wbc count 21000. he has a severe infection in his throat, some times blood with his saliva. is it dangerous ?

Indicates infection: WBC counts more than 20k are not uncommon with severe infections including the ones in throat region. Just make sure he is seen by qualified physician for his treatment, that would probably require antibiotic and some oral mouthwash. You doctor after exam can determine if any other tests/ X rays Re needed.

Elevated WBC: If he is on correct antibiotics and being followed closely by a Doctor and perhaps along with ENT Doctor he should get better . Please stay in touch with his physician.

Kill! Maim! Destroy!: I assume he's seen a doctor to treat the throat problem? The'white count'in children can be deceiving. Better to treat the child than the numbers. Unless...the cells seen on the white count look funny or abnormal. I'm sure they'll tell you about that.Otherwise, his white cells are out there in the field doing their job (kill! maim! destroy!).Nothing will be dangerous if attended by a competent doc

Talk to doctor: Your son may be having throat infection and tonsils ,one may get little blood from throat specially after straining or coughing. It should go away as the infection subsides .Better speak to the treating doctor and get his throat examination done for bleeding