Is low sodium normal in lung cancer. all other tests are fine. so us it cancet?

Limited use: A really low serum sodium (not just slightly low) suggests either end-stage wasting or inappropriate ADH (vasopressin) secretion by a small-cell carcinoma. Bloodwork is of no real value in the diagnosis of lung cancer; a biopsy of any suspicions lesion is required and when read by the pathologist establishes the diagnosis, whatever the bloodwork may say about the rest of one's health screen.

Pathologist: The diagnosis of cancer is definitively done by a pathologist examining the tumor under the microscope and inmunohistochemical and/or genetic testing on the tissue. Anything else is speculation.

See below: Sometimes lung cancer produce hormones that can cause low sodium; this may be related to the cancer, often seen in a form of lung cancer called small cell lung cancer.