A "poor" creatinine level isn't a single value but rather depends on whether the level is too high or too low, and also on the individual's sex and muscle mass. Both high and low creatinine can indicate underlying health problems.
High Creatinine Levels: A Sign of Kidney Problems
High creatinine levels, generally above 1.2 mg/dL in males and 1.1 mg/dL in females, often signal impaired kidney function. The kidneys' inability to effectively filter creatinine from the blood leads to its accumulation. This is because creatinine is a waste product produced when the body uses creatine for energy; healthy kidneys efficiently remove it. Elevated admission serum creatinine, for instance, is associated with poor myocardial flow and prognosis in certain heart conditions. (https://pubmed.ncbi.nlm.nih.gov/19805833/) As the Mayo Clinic notes, an increased level of creatinine may be a sign of poor kidney function. (https://www.mayoclinic.org/tests-procedures/creatinine-test/about/pac-20384646) Furthermore, serum creatinine is considered an inadequate screening test for renal failure because it's a poor indicator of kidney function early in the disease process. (https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/215075)
Low Creatinine Levels: Potential Muscle or Liver Issues
Conversely, low creatinine levels (below 0.6 mg/dL in males and 0.5 mg/dL in females) may suggest problems with muscle mass, liver function, or significant fluid overload. Reduced muscle mass, for example, naturally leads to lower creatinine production. (https://www.medicalnewstoday.com/articles/319892, https://www.healthline.com/health/low-creatinine, https://pmc.ncbi.nlm.nih.gov/articles/PMC4958791/) In amyotrophic lateral sclerosis (ALS), decreasing creatinine levels alongside rising ferritin levels are associated with a poor prognosis. (https://pubmed.ncbi.nlm.nih.gov/26095828/)
Important Note: A creatinine level alone doesn't provide a complete picture. Doctors consider it alongside other factors to diagnose conditions. A normal range varies depending on age, sex, muscle mass, and other individual factors.
