[Impaired renal function: be aware of exogenous factors]

Area of Science:

• Nephrology
• Clinical Chemistry
• Nutritional Science

Background:

• Renal function is commonly estimated using the Modification of Diet in Renal Disease (MDRD) formula, which relies partly on serum creatinine.
• Patients with declining renal function are referred to nephrologists per national guidelines for chronic renal impairment.

Observation:

• A 54-year-old woman with no significant medical history was referred due to a coincidental decline in estimated glomerular filtration rate (eGFR).
• The patient was asymptomatic and only taking creatine supplements; other diagnostic tests revealed no abnormalities.

Findings:

• Serum creatinine levels are influenced by muscle mass.
• Creatine supplementation, including creatine ethyl ester, can elevate serum creatinine, thereby affecting the calculated eGFR using the MDRD formula.
• Discontinuation of creatine supplements led to the normalization of the patient's renal function estimates.

Implications:

• Healthcare providers should inquire about creatine and other dietary supplement use when assessing renal function.
• Accurate estimation of glomerular filtration rate (eGFR) requires consideration of factors that can artificially alter serum creatinine levels.
• Understanding the impact of supplements on renal biomarkers is crucial for appropriate patient management and referral decisions.