At this age hemoglobin level varies from 10.5-13.5.
There can be variation among labs.
The cause of falling hemoglobin level needs to be determined.
After 1 year there can be deficiency in iron due to less intake of iron rich cereals or food.
Drinking a lot of cow's milk can cause less intake of other iron rich food leading to anemia.
He would need supplements & follow up after a few months.
Please try to give him iron rich food.
Here is a link on it.
There can be blood loss with stool.
A stool test can be taken if not done already.
I hope this information will be helpful.
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Wish his healthy life.