Low levels of serum creatinine in the blood often indicate muscle disorders, including myasthenia gravis and muscular dystrophy, states MedlinePlus. In myasthenia gravis, connections between muscles and their nerves are blocked. Muscular dystrophy refers to many diseases characterized by muscle weakness and loss of muscle mass, Mayo Clinic reports.
In women, normal levels of serum creatinine are between 0.6 and 1.1 milligrams per deciliter, according to MedlinePlus. A normal reading for men ranges from 0.7 to 1.3. The difference is due to women's comparatively lower muscle mass. Creatinine is a waste product filtered by the kidneys, so physicians typically order serum creatinine tests to measure kidney function.