Pancreatic enzymes

10 DOH Abu Dhabi (HAAD) lab licensing practice questions on Pancreatic enzymes, part of Clinical Chemistry. The first 10 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A 58-year-old woman on chemotherapy for serous ovarian carcinoma has had a raised amylase on every routine panel for 2 months, without abdominal pain or swelling of the parotid glands. Results: total amylase 1,250 U/L (reference 30-110), pancreatic (P-type) amylase 34 U/L (reference 13-53), lipase 41 U/L (reference below 60) and creatinine 68 µmol/L (0.77 mg/dL). The amylase-to-creatinine clearance ratio from a random urine is 3.8% (reference 1-5%). Abdominal CT shows a normal pancreas. The most likely source of the raised amylase is:

   1. AReduced renal clearance of amylase
   2. BMacroamylase in the plasma
   3. CPancreatic injury from chemotherapy
   4. DSalivary-type amylase from the tumor

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   Answer: D · Salivary-type amylase from the tumor

   Almost all of the amylase is non-pancreatic: P-type amylase is normal, so about 1,200 U/L is salivary (S-type) isoamylase. Normal lipase, P-type amylase and pancreatic CT exclude pancreatic injury. A normal amylase-to-creatinine clearance ratio shows the amylase is filtered and cleared normally, which rules out macroamylasemia (ratio typically below 1%) and reduced renal clearance. Some tumors, notably ovarian and lung carcinomas, secrete S-type amylase, and with no parotid disease the tumor is the likely source. Isoamylase or P-type amylase testing is the key step whenever amylase is raised without a matching rise in lipase.

   • A: Creatinine and the clearance ratio are normal, so renal clearance is not reduced.
   • B: Macroamylase is not filtered, so the clearance ratio would be low, not 3.8%.
   • C: Lipase, P-type amylase and the pancreas on CT are all normal.

2. Question 2 · Medium

   A 7-year-old has fever and painful swelling in front of both ears. Serum amylase is 410 U/L (reference 30-110 U/L) and lipase is 35 U/L (reference below 60 U/L). What is the most likely source of the amylase?

   1. AMacroamylase complexes
   2. BInflamed pancreas
   3. CInflamed salivary glands
   4. DReduced renal clearance

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   Answer: C · Inflamed salivary glands

   Swelling in front of the ears is parotitis, often mumps, and it releases salivary (S-type) amylase. Lipase comes almost only from the pancreas, so a normal lipase argues against pancreatitis. Mumps can involve the pancreas, but lipase would then rise as well. Lipase or pancreatic amylase is used to separate the two sources.

   • A: Macroamylasemia causes no symptoms and does not fit acute parotid swelling.
   • B: Pancreatitis would raise lipase as well.
   • D: Nothing suggests renal impairment, and it would usually raise lipase too.

3. Question 3 · Medium

   Which laboratory test helps confirm macroamylasemia in a patient with a persistently raised serum amylase?

   1. APolyethylene glycol (PEG) precipitation
   2. BSalivary amylase inhibition assay
   3. CAmylase measured on EDTA plasma
   4. DHeat inactivation of serum at 56 °C

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   Answer: A · Polyethylene glycol (PEG) precipitation

   Macroamylase is amylase bound to an immunoglobulin, usually IgA or IgG, or to a polysaccharide, so it is too large to be filtered. PEG precipitates the immunoglobulin complexes, and a low recovery of amylase activity in the supernatant supports macroamylase. Gel filtration chromatography is the reference method, and a low amylase-to-creatinine clearance ratio is supportive. Recognizing it avoids needless imaging.

   • B: Isoenzyme inhibition tells salivary from pancreatic amylase, not bound from free.
   • C: EDTA chelates calcium and falsely lowers amylase.
   • D: Heat inactivation is used to separate bone and liver ALP.

4. Question 4 · Hard

   A woman with no abdominal symptoms has a persistently raised amylase. Random results: serum amylase 450 U/L, urine amylase 90 U/L, serum creatinine 80 µmol/L, urine creatinine 8.0 mmol/L. What is the amylase-to-creatinine clearance ratio (ACCR)?

   1. A0.2%
   2. B0.002%
   3. C20%
   4. D200%

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   Answer: A · 0.2%

   ACCR (%) = (urine amylase x serum creatinine) ÷ (serum amylase x urine creatinine) x 100, with both creatinines in the same unit. Urine creatinine 8.0 mmol/L = 8,000 µmol/L, so ACCR = (90 x 80) ÷ (450 x 8,000) x 100 = 0.2%. The usual ratio is about 1-4%, and a value below 1% supports macroamylasemia, because the bound enzyme is not filtered. PEG precipitation can then confirm it.

   • B: 0.002% leaves out the factor of 100.
   • C: 20% uses only the amylase ratio and leaves out creatinine.
   • D: 200% mixes µmol/L and mmol/L for creatinine.

5. Question 5 · Easy

   Apart from the pancreas, the main source of amylase in normal serum is the:

   1. AKidney
   2. BLiver
   3. CSalivary glands
   4. DSkeletal muscle

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   Answer: C · Salivary glands

   Serum amylase is a mixture of pancreatic (P-type) and salivary (S-type) isoenzymes, and in health a little over half is S-type. Parotitis, such as mumps, raises S-type amylase without pancreatic disease. Amylase is small enough to be filtered by the glomerulus and appears in urine. A raised total amylase alone is therefore not specific for pancreatitis.

   • A: The kidney clears amylase; it does not supply it.
   • B: The liver is not an important source of serum amylase.
   • D: Skeletal muscle releases CK and LD, not amylase.

6. Question 6 · Easy

   Which bonds in starch does alpha-amylase hydrolyze?

   1. ABeta-1,4 glycosidic bonds
   2. BAlpha-1,6 branch-point bonds
   3. CInternal alpha-1,4 glycosidic bonds
   4. DEster bonds between glycerol and fatty acids

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7. Question 7 · Medium

   Many laboratories measure pancreatic amylase separately from salivary amylase by:

   1. APrecipitating salivary amylase with polyethylene glycol
   2. BHeat-inactivating the salivary amylase at 56 °C
   3. CBlocking pancreatic amylase activity with EDTA
   4. DInhibiting S-type amylase with monoclonal antibodies

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8. Question 8 · Easy

   In acute pancreatitis, the usual biochemical criterion for diagnosis (revised Atlanta classification) is serum lipase or amylase of at least:

   1. AThree times the upper reference limit
   2. BThe upper reference limit itself
   3. CTwice the upper reference limit
   4. DTen times the upper reference limit

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9. Question 9 · Medium

   Amylase activity measured on EDTA plasma is falsely low because EDTA:

   1. APrecipitates the amylase protein
   2. BLowers the pH of the reaction
   3. CChelates the calcium the enzyme needs
   4. DReleases zinc that inhibits amylase

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10. Question 10 · Hard

    A 38-year-old man with poorly controlled diabetes has had severe epigastric pain for 12 hours. His serum is milky, with triglycerides 28 mmol/L (2,480 mg/dL). Amylase is 95 U/L (reference 30-110 U/L), lipase 820 U/L (reference below 60 U/L), and CT shows acute pancreatitis. What best explains the normal amylase?

    1. ASevere hypertriglyceridemia can mask the amylase rise
    2. BPancreatitis from high triglycerides releases no amylase
    3. CAmylase has already returned to its normal range
    4. DLipemia has falsely raised the lipase result

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