Fractional Excretion of Amylase (FE _Amy ) may be clinically useful in determining presence of acute pancreatitis, macroamylasemia and postoperative pancreatitis. This test is rarely used as lipase is typically more specific and other imaging tests are utilized. The specificity of this test may also be poor, especially in patients with renal insufficiency.

Amylase and Creatinine must be measured in both the serum and urine in order to calculate FE _Amy .

The formula is:

• FE _Amy =100*(U _Amy *S _Cr )/(S _Amy *U _Cr )
• FE _Amy =% Excretion of Amylase
• U _Amy =Urine Amylase in U/L
• S _Cr =Serum creatinine in mg/dl
• S _Amy =Serum amylase in U/L
• U _Cr =Urine creatinine in mg/dl

Interpretation:

• Normal: 1-5%
• Macroamylasemia: <1%
• Acute pancreatitis: >5%

Normal range in postoperative patients, especially on successive daily testing may be useful in excluding the diagnosis of postoperative pancreatitis.

Reference:

• Lankisch PG, Koop H, Otto J, et al. Specificity of increased amylase to creatinine clearance ratio in acute pancreatitis. Digestion. 1977;16(1-2):160-4.
• Leckie PA, Ferreira P, Debas HT. Assessment of the amylase--creatinine clearance ratio in postoperative patients. Ann Surg. 1980;192(2):195-8.
• Ligny G, Meunier JC, Hayard P, et al. [Sensitivity and specificity of blood amylase, amylase and creatinine clearance ratio and urinary amylase/urinary creatinine ratio in the diagnosis of acute pancreatitis]. Gastroenterol Clin Biol. 1987;11(12):880-5.
• Warshaw AL, Fuller AF. Specificity of increased renal clearance of amylase in diagnosis of acute pancreatitis. N Engl J Med. 1975;292(7):325-8.