When I was seriously underweight, my labs came back largely normal. My doctors all thought this meant I wasn't in as serious of a condition as my weight indicated, and seeing my normal labs also reassured me. They were surprised how my labs were normal given I was so visibly ill.
Dr. Jennifer Gaudiani's Sick Enough explains how "normal labs" in someone who is restricting food are no sign of health.
Here are excerpts from her book (emphasis mine):
"Patients who restrict calories can have many medical problems that do not cause the blood tests to become abnormal.
It turns out that nearly every patient who purely restricts—that is, does not purge—has normal labs.
How can this be? How can a patient who has regrown fetal facial hair, has cold hands and feet, a hibernating heart, slowed digestion, and anxiety and obsessiveness from a starved brain possibly have normal bloodwork? The answer once again lies in our amazing cave person brain, which evolved to keep us safe during famine. Virtually no patient with anorexia nervosa stops eating altogether.
Some of my patients have said to me, “I’m not sick, Dr. G. I mean, I’m eating something every day.” Even in those who eat very little, the body fiercely defends its electrolyte homeostasis, carefully balancing out electrolytes to keep the body on an even keel.”
As Dr. Gaudiani has said in an interview, you wouldn’t wait until your dogs’ labs look abnormal for you to give them food and water. So don't wait for your own labs to look abnormal, which might not happen, for you to take action.