Urine Analysis: Part 17 – Urine amylase (Amylasuria), Amylase/Creatinine clearance ratio
- The sample is urine.
- Can obtain random 2 hours urine sample.
- Amylase is unstable in acidic urine so adjust pH to alkaline range.
- Store urine at 4 °C.
- Or can collect 24 hours sample. Discard the first sample and then collect the rest of 24 hours sample in the container, including the last sample.
- Also, collect venous blood to make the serum for the serum amylase level.
- For blood tests, don’t eat or drink for at least 2 hours.
- Urine amylase is unstable in acidic urine. Acid urine decreases the amylase levels.
- Adjust the pH to 7.0.
- Refrigerate the urine.
- Avoid urine contamination by stool.
Purpose of the test (Indications)
- This test tells about pancreatic dysfunction.
- It differentiates acute pancreatitis from other:
- abdominal pain.
- Epigastric discomfort.
- Nausea and vomiting.
- It diagnoses pancreatitis in the late stages when the blood amylase is normal.
- The amylase enzyme changes starch to sugar.
- Amylase is described into two forms:
- α-Amylase found in the human.
- β-Amylase is found in plants and bacteria.
- Amylase enzymes change starch into sugars.
- Large polysaccharide molecules are broken into smaller units of dextrin, maltose, and glucose.
- Normally the low level of amylase is found in the blood and excreted in a small amount in the urine.
- When the pancreas and salivary glands are inflamed, then much more enzyme enters the blood, and as a result, more amylase is excreted in the urine.
- In the case of pancreatitis, amylase level is raised in the blood for a short time, while in the urine remains for several days.
- The site of formation of amylase:
- Salivary glands.
- Liver (little or no amylase activity).
- Fallopian tubes.
- Amylase activity also found in:
- Semen, testes.
- Ovaries, fallopian tubes.
- Striated muscles.
- Adipose tissue.
- Colostrum and milk.
- The tears.
- Amylase from pancreatic acini goes through the pancreatic duct into the duodenum.
- Once in the intestine, it converts carbohydrates into simple sugars.
- Excretion of amylase:
- An Amylase is a small unit, and it can pass through the glomeruli and is found in the urine.
- Urinary amylase clearance is increased in acute pancreatitis from normal to 3 folds.
- A value of >550 U/L has a sensitivity of 62% and 97% specific for acute pancreatitis.
- In damage to the salivary glands or pancreas, more enzyme in the blood is excreted in the urine.
- In pancreatitis:
- A prolonged raised level of amylase in urine may be raised until 5 to 7 days.
- The short-lived peak in blood, maybe 1 to 2 days and return to normal.
- In acute pancreatitis Amylase picture is:
- The initial rise of 2 to 12 hours.
- The peak level is 12 to 72 hours.
- The normal level reaches 3 to 4 days (short-lived peak).
- Urine amylase may remain elevated up to 2 weeks after the acute episode of acute pancreatitis.
Amylase/creatinine clearance ratio:
- This is done on a single random urine sample and a single serum sample, instead of 2 hours or 24 hours.
- The calculation of the amylase/creatine clearance ratio normally is 1 to 4%.
- 1 to 17 U/hour
- 170 to 2000 U/L
- Abbott TDX = 5 to 27 U/h.
- Up to 5000 Somogyi units /24 hours Or
- 6.5 to 48.1 units/hour.
- 2 hours sample = 2 to 34 U
- 24 hours sample = 24 to 408 U.
- Another reference gives a normal range = 1 to 17 U/h.
- So different kits have a different range.
Increase urine Amylase level seen in:
- Acute Pancreatitis.
- Chronic relapsing pancreatitis.
- Penetrating peptic ulcer to the pancreas.
- Acute cholecystitis.
- Parotitis (mumps), called sialadenitis.
- Ruptured ectopic pregnancy.
- Pulmonary infarction.
- Autoimmune diseases.
- Pancreatic cyst.
- Biliary tract disease.
- Diabetic ketoacidosis.
- Intestinal obstruction.
- Few lung or ovarian tumors.
Decreased urine Amylase is seen in:
- Pancreatic Insufficiency.
- Renal failure.
- Liver disease (severe).
- Advanced cystic fibrosis.
Amylase/creatinine clearance ratio is increased in:
- Toxemia of pregnancy.
- Diabetic ketoacidosis.
- Renal insufficiency.
Normal urine picture:
Physical features Chemical features Microscopic findings
- Color = Pale yellow or amber
- Appearance = Clear to slightly hazy
- pH = 4.5 to 8.0
- Specific gravity = 1.015 to 1.025
- Blood = Negative
- Glucose = Negative
- Ketones= Negative
- Protein = Negative
- Bilirubin = Negative
- Urobilinogen = Negative (±)
- Leucocyte esterase = Negative
- Nitrite for bacteria = Negative
- RBCs = Rare or Negative
- WBC = Rare or Negative
- Epithelial cells = Few
- Cast = Negative (Occasional hyaline)
- Crystal = Negative (Depends upon the pH of the urine)
- Bacteria = Negative
- The amylase/creatinine clearance ratio is decreased in macroamylasia.