Interpretative Information

Chymotrypsins are pancreatic enzymes, released into pancreatic duct, responsible for break down of proteins in the gut.  A reduced concentration of fecal chymotrypsins has been used as a marker for pancreatic exocrine insufficiency.

Fecal chymotrypsin versus fecal pancreatic elastase test:

1. Chymotrypsin activity is reduced in more acidic faeces. Optimum pH is 8.5-9.5. Pancreatic elastase is stable in acidic pH.
2. Method of testing is different: In fecal chymotrypsin, chymotrypsin enzyme activity is measured.  In fecal pancreatic elastase, elastase quantity is measured
3. Both chymotrypsin and pancreatic elastase are not very sensitive for mild pancreatic exocrine insufficiency. Chymotrypsin detects around 25% of mild disease. Pancreatic elastase is slightly better.
4. Chymotrypsin detects around 86% of severe pancreatic disease, 50% of moderate pancreatic disease. Majority of studies show pancreatic elastase better sensitivity for moderate to severe pancreatic insufficiency than chymotrypsin. 
5. Pancreatic elastase is not capable of assessing pancreatic supplement response - chymotrypsin is contained in pancreatic supplements but not elastase. However, if the intrinsic pancreatic function is to be assessed, prior withholding of pancreatic supplement is not required for pancreatic elastase test.

False positives (non-structural pancreatic diseases) :

1. Watery diarrhea
2. In intestinal mucosal atrophic diseases  e.g  celiac disease or in protein malnutrition state -  functional pancreatic insufficiency secondary to reduced enterohormones  
3. Uraemic pancreatopathy - no gross anatomical features but histological features similating chronic pancreatitis

False negatives :

1. Mild pancreatic insufficiency
2. Post antibiotic therapy, presumably by reducing bacterial degradation or inhibition on the enzyme (ref: Remtulla MA   Clin Biochem 1986; 19:341-347)
3. Post ileal resection and radiation ileitis (especially distal ileal disease) - presumably reflect removal of an inhibitory mechanism on pancreatic secretion

Fecal chymotrypsin and daily fecal fat excretion

Fecal chymotrypsin bears no direct relationship with fecal fat excretion and cannot distinguish healthy subjects from patients with pancreatic and/or non-pancreatic steatorrhoea.

References:

Moss DW, Henderson AR.   Clinical enzymology (chapter 22) in Tietz textbook of Clinical Chemistry (3^rd edition, 1999) Burtis CA, Ashwood ER (eds) W.B. Saunders company, Philadelphia, Pennsylvania

Chowdury RS et al   Aliment Pharmacol Ther 2003; 17:733-750

Remtulla MA et al   Clin Biochem 1986; 19:341-347

Carroccio A et al     Gut 1991; 32:796-9

Ventrucci M et al    Dig Dis Sci 2000; 45(11): 2265-69

Stockbrugger RW et al   Scan J Gastroenterol suppl 1991; 188:13-9