Kidney Function: Kidneys are essential for micro-managing your blood chemicals. They’re often the first organs hit by chronic disease.

  • Creatinine: Muscle metabolism generates this protein waste product, and then the kidneys eliminate it. Depending on muscle mass, creatinine is released at a constant rate. So this serum level is a good indicator of kidney function. Creatinine levels can rise temporarily as a result of muscle injuries.
  • BUN: This measures the amount of urea nitrogen in the blood. Urea contains nitrogen and is the major breakdown product of bodily protein. The kidneys usually eliminate urea and other nitrogen-rich waste products from the bloodstream. An increased BUN level can indicate impaired renal (kidney) function. However, dehydration also may cause an elevated BUN level.

Liver Disease: The liver filters the body’s toxins and is the main metabolic engine for making new proteins. There are tons of different kinds of liver diseases, from hepatitis to cirrhosis (liver scarring).

  • AST: Aspartate aminotransferase (AST) is an enzyme in the muscle, liver and heart tissues. High levels of AST can be seen with liver diseases like hepatitis. Injury or disease to the muscles can also cause this rise in AST. The AST test is usually done to determine liver function in conjunction with other tests, like alkaline phosphatase (ALP) and aminotransferase (ALT).
  • Bilirubin: This breakdown product comes from hemoglobin release from dying red blood cells. It’s elevated if the gallbladder or liver is too congested to process this waste product.

Heart Failure: The heart can’t pump enough blood to the body. It’s hard to understand why fatigue occurs. Symptoms can include shortness of breath and leg swelling. Diet changes and quitting smoking could avoid this condition.

  • B-Type Natriuretic Peptide (BNP): This is made only in the heart ventricles. High levels can indicate heart failure. There’s a strong connection between the degree of heart failure and the BNP level. BNP may have important prognostic importance for people with acute coronary syndrome (ACS). If your BNP is significantly high, heart disease may be causing your fatigue.

QUIZ: How Healthy Are You?