Muscle wasting or decreased muscle mass: Low creatinine levels can be seen in individuals with reduced muscle mass, as creatinine is a byproduct of muscle metabolism. Conditions such as muscular dystrophy, amyotrophic lateral sclerosis (ALS), or severe malnutrition can lead to decreased muscle mass and subsequently low creatinine levels.

Pregnancy: During pregnancy, creatinine levels may decrease due to increased renal blood flow and glomerular filtration rate.
Vegans or vegetarians: Individuals who follow a plant-based diet may have lower creatinine levels due to reduced muscle mass or differences in muscle metabolism.
Elderly: Older adults may have lower creatinine levels due to age-related decline in muscle mass.

Rhabdomyolysis: Although rhabdomyolysis typically presents with elevated creatinine levels, in the early stages, creatinine levels may be low due to the rapid breakdown of muscle tissue. It is crucial to consider this diagnosis, as delayed treatment can lead to severe complications.
Severe liver disease: Liver dysfunction can affect creatinine production and excretion, leading to low creatinine levels. Missing this diagnosis can have significant consequences, as liver disease can progress rapidly.

Glycogen storage diseases: Certain glycogen storage diseases, such as McArdle disease, can affect muscle metabolism and lead to low creatinine levels.
Cystic fibrosis: Some individuals with cystic fibrosis may have low creatinine levels due to malnutrition and decreased muscle mass.
Hypothyroidism: Severe hypothyroidism can lead to muscle weakness and decreased muscle mass, resulting in low creatinine levels.