The amylase-creatinine clearance may be calculated if random, simultaneously collected serum and urine samples are analyzed for both creatinine and amylase.
Specimen Collection:
(1) Simultaneous collection and analysis of serum and urine are important.
(2) Because of the ratio cancels out volumes and units, a timed urine collection is not required
amylase-to-creatinine clearance ratio =
= ((urine amylase in U/L) / (serum amylase in U/L)) * ((serum creatinine in mg/dL) / (urine creatinine in mg/dL)) * 100
Interpretation:
• A clearance ratio of 1-5% is normal. About 30% of patients with acute pancreatitis show a normal ratio during the acute course of illness.
• A clearance ratio less than 1% indicates macroamylasemia (polymerization of amylase to amylase or to immunoglobulins.
• A clearance ratio more than 5% indicates acute pancreatitis, but may also occur in burns, diabetic ketoacidosis, acute defects in renal tubular function, severe renal insufficiency, duodenal perforation, and pancreatic cancer.
• The ratio has not proven as useful as initially felt for the diagnosis of acute pancreatitis, due to methodologic problems and poor diagnostic efficiency. Thus, an elevated ratio is not recommended for diagnosis of acute pancreatitis.
