Urine amylase (Amylasuria), Amylase/Creatinine clearance ratio

Sample

1. The sample is urine.
2. Can obtain random 2 hours urine sample.
3. Amylase is unstable in acidic urine so adjust pH to alkaline range.
4. Store urine at 4 °C.
   1. 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.
5. Also, collect venous blood to make the serum for the serum amylase level.
6. For blood tests, don’t eat or drink for at least 2 hours.

Precautions

1. Urine amylase is unstable in acidic urine. Acid urine decreases the amylase levels.
2. Adjust the pH to  7.0.
3. Refrigerate the urine.
4. Avoid urine contamination by stool.

Purpose of the test (Indications)

1. This test tells about pancreatic dysfunction.
2. It differentiates acute pancreatitis from other:
   1. abdominal pain.
   2. Epigastric discomfort.
   3. Nausea and vomiting.
3. It diagnoses pancreatitis in the late stages when the blood amylase is normal.

Pathophysiology

1. The amylase enzyme changes starch to sugar.
2. Amylase is described into two forms:
   1. α-Amylase found in the human.
   2. β-Amylase is found in plants and bacteria.
   3. Amylase enzymes change starch into sugars.
3. Large polysaccharide molecules are broken into smaller units of dextrin, maltose, and glucose.
4. Normally the low level of amylase is found in the blood and excreted in a small amount in the urine.
   1. 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.
5. In the case of pancreatitis, amylase level is raised in the blood for a short time, while in the urine remains for several days.
6. The site of formation of amylase:
   1. Salivary glands.
   2. Pancreas.
   3. Liver (little or no amylase activity).
   4. Fallopian tubes.
      

      Amylase source

6. Amylase activity also found in:
   1. Semen, testes.
   2. Ovaries, fallopian tubes.
   3. Striated muscles.
   4. Lungs.
   5. Adipose tissue.
   6. Colostrum and milk.
   7. The tears.
7. Amylase from pancreatic acini goes through the pancreatic duct into the duodenum.

8. Once in the intestine, it converts carbohydrates into simple sugars.
9. Excretion of amylase:
   1. An Amylase is a small unit, and it can pass through the glomeruli and is found in the urine.
10. Urinary amylase clearance is increased in acute pancreatitis from normal to 3 folds.
11. A value of >550 U/L has a sensitivity of 62% and 97% specific for acute pancreatitis.
12. In damage to the salivary glands or pancreas, more enzyme in the blood is excreted in the urine.
13. In pancreatitis:
    1. A prolonged raised level of amylase in urine may be raised until 5 to 7 days.
    2. The short-lived peak in blood, maybe 1 to 2 days and return to normal.
    3. In acute pancreatitis Amylase picture is:
       1. The initial rise of 2 to 12 hours.
       2. The peak level is 12 to 72 hours.
       3. The normal level reaches 3 to 4 days (short-lived peak).
       4. Urine amylase may remain elevated up to 2 weeks after the acute episode of acute pancreatitis.

Amylase/creatinine clearance ratio:

1. This is done on a single random urine sample and a single serum sample, instead of 2 hours or 24 hours.
2. The calculation of the amylase/creatine clearance ratio normally is 1 to 4%.

Normal

Source 1

• 1 to 17 U/hour
• 170 to 2000 U/L
• Abbott TDX =  5 to 27 U/h.

Source 2

• Up to 5000 Somogyi units /24 hours Or
• 6.5 to 48.1 units/hour.

Sources 4

• 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:

1. Acute Pancreatitis.
2. Chronic relapsing pancreatitis.
3. Penetrating peptic ulcer to the pancreas.
4. Acute cholecystitis.
5. Parotitis (mumps), called sialadenitis.
6. Ruptured ectopic pregnancy.
7. Pulmonary infarction.
8. Autoimmune diseases.
9. Pancreatic cyst.
10. Peritonitis.
11. Biliary tract disease.
12. Diabetic ketoacidosis.
13. Intestinal obstruction.
14. Few lung or ovarian tumors.

Decreased urine Amylase is seen in:

1. Pancreatic Insufficiency.
2. Renal failure.
3. Liver disease (severe).
4. Advanced cystic fibrosis.

Amylase/creatinine clearance ratio is increased in:

1. Pancreatitis.
2. Toxemia of pregnancy.
3. Diabetic ketoacidosis.
4. 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.

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