More Details are needed.
since birth- How frequently he used to vomit? What was said by doctors when he was a baby? What medications were given? How was the weight gain during infancy? Usual cause of recurrent vomiting in infants is Reflux.
Now, at this age of 4.5 yrs, what is his weight? Please feel free to get back with all details.
Vomiting brown fluids to the level of dehydration- surely he needs to be evaluated thoroughly.
Usually brown fluids indicate a bleed- that in contact with gastric juices- becomes brown in color. Most common cause is severe gastritis
And CRP of 125 indicates severe infection. Blood glucose
can be low in severe infections.
You have not mentioned the value of blood urea. If both urea and creatinine
are higher- it indicates his kidney
is involved in the illness.
You have not mentioned anything else like fever
his symptoms. With the details provided, one cannot conclude what the entire problem is.
How ever he needs to be hospitalized and evaluated thoroughly for the same.
I would like to check his development mile stones as well- to rule out any metabolic disorders- which can present with recurrent vomiting- along with other symptoms like developmental delay etc.
Hope my answer helps you.
Wish your son a speedy recovery.