Chymotrypsin (Faeces)

Diagnostic Use

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

Interpretation

Faecal chymotrypsin (FCT) versus faecal pancreatic elastase (FPE) test  :

1. FCT activity is reduced in more acidic faeces. Optimum pH is 8.5-9.5. FPE is stable in acidic pH.
2. Method of testing is different: In FCT, chymotrypsin enzyme activity is measured.  In FPE, elastase quantity is measured
3. Both FCT and FPE are not sensitive for mild pancreatic exocrine insufficiency. FCT detects around 25% of mild disease.
4. FCT detects around 86% of severe pancreatic disease, 50% of moderate pancreatic disease. Majority (not all) studies suggest FPE has slightly better sensitivity for moderate to severe pancreatic insufficiency than FCT.
5. FPE test carries a higher cost
6. FPE 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 FPE test.

False positives (non-structural pancreatic diseases) :

1. Watery diarrhoea
2. In intestinal mucosal atrophic diseases  e.g  coeliac 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

Faecal chymotrypsin and daily faecal fat excretion

FCT bears no direct relationship with faecal fat excretion and cannot distinguish healthy subjects from patients with pancreatic and/or non-pancreatic steatorrhoea

References:

1. 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
2. Chowdury RS et al   Aliment Pharmacol Ther 2003; 17:733-750
3. Remtulla MA et al   Clin Biochem 1986; 19:341-347
4. Carroccio A et al     Gut 1991; 32:796-9
5. Ventrucci M et al    Dig Dis Sci 2000; 45(11): 2265-69
6. Stockbrugger RW et al   Scan J Gastroenterol suppl 1991; 188:13-9

Also see Pancreatic Elastase

Reference Intervals

Units: U/g of wet stool