Creatinine and Blood Urea Nitrogen (B111)

Low blood creatinine is associated with liver dysfunction, muscle wasting, and sarcopenia whereas high blood creatinine is associated with kidney disease.  Creatinine is a metabolic product of creatine phosphate which is the main energy source for muscles. Typically, due to higher overall muscle mass, men have naturally higher levels of creatine phosphate. Creatine, the metabolic precursor of creatine phosphate is not made in muscles but is made via an inter-organ metabolic system where GAA (guanidino acetic acid) is made in the kidney and then GAA is converted to creatine in the liver via a methyltransferase reaction. Accordingly, healthy muscle maintenance is dependent upon healthy liver methyltransferase capacity. High homocysteine levels are indicative of reduced methyltransferase capacity either due to excessive methyltransferase active or impaired homocysteine recycling back to methionine. 

To access the FREE seminars with full presentations and videos please visit Dr. Goodenowe’s resource site here. This is the article for seminar B111, Blood Tests and Biomarkers (Series B).

Since creatinine is eliminated by the kidneys, a high blood creatinine level is a biomarker of potential renal dysfunction. High blood creatinine levels are also observed under conditions of strenuous exercise. 

Since your muscles need creatine to maintain their function and blood creatinine is derived from the breakdown of creatine phosphate, a low blood creatinine level is a biomarker of potential liver dysfunction, muscle wasting, or sarcopenia.  

Omega-3 supplementation reduces high serum creatinine in patients undergoing dialysis. Omega-3 supplementation is strongly preventative of end stage renal disease and delays progression of the disease. 

Blood Urea Nitrogen (BUN) is an older, less accurate test regarding kidney function. Urea is a break down product of proteins, so BUN is a combination of internal and dietary protein digestion and kidney clearance. It should be viewed in context with creatinine and not by itself. Low BUN relative to normal creatinine is linked to malnutrition and liver disease. A high BUN relative to creatinine is linked to high protein intake. 

Dr. Goodenowe explains the relevant literature regarding blood creatinine levels in seminar B111 – Creatinine and Blood Urea Nitrogen.