Creatinine is a product that forms when creatine phosphate, a component of muscle tissue, is broken down. As this creatinine builds up in the blood, it is filtered into the urine by the kidneys. If the kidney function has been impaired by strong medications, creatinine levels will increase in the blood, due to decreased excretion of creatinine in the urine.
One of the lab tests that CF patients should have done every year is a creatinine blood test. The results of the test will show how well the kidneys are functioning. This is important to monitor, especially for patients who are frequently prescribed antibiotics.
Normal levels fall in the range of 0.8 to 1.4 mg/dl.
In people with CF, high concentrations of creatinine can be attributed to dehydration, or kidney failure. Cephalosporins and aminoglycosides are types of antibiotics that are typically prescribed for CF patients. These medications are known to be nephrotoxic (i.e. harmful to kidneys) and can result in high creatinine levels.