What blood albumin number would indicate severe dehydration? (on a lab where 3.5-5 was the normal range)

It doesn't. Albumin is a blood protein. It does not detect dehydration. Clinical signs of dehydration are dry mucous membranes, low blood pressure, rapid, thready (hard to feel) pulse. BUN and creatinine blood values may be helpful. Albumin can be low with poor nutrition, malabsorption, or certain types of kidney disease.

Related Questions

What does high Blood Albumin indicate? What would you think of a 5.8 blood albumin? Severe dehydration? Long-term consequences for weeks at this #?

Likely dehydration. There are few pathological conditions that result in high serum albumin, except dehydration. Drink enough water so that your urine is clear, colorless and odorless, i.e., watery before repeating the test. If you had injection of contrast medium before the test, that may result in a spurious high reading of albumin. Read more...