The acid steatocrit is rapid method to estimate the amount of fat excretion in the stool. It is similar to the capillary hematocrit and is considerably more convenient than a conventional 72 hour stool analysis. It can be used to monitor a patient's response to therapy.
Method:
(1) 0.5 grams of feces from a spot collection are diluted 1 to 4 with deionized water.
(2) The specimen is homogenized using a tissue homogenizer.
(3) A volume of 5 N perchloric acid equal to 20% of the homogenate volume is added, and the mixture is then vortexed for 30 seconds.
(4) The acid-homogenate mixture is placed in a 75 µL plain glass hematocrit capillary tube.
(5) The capillary tube is then centrifuged horizontally at 13,000 rpm for 15 minutes in a standard centrifuge.
(6) This will separate fat as an upper layer overlying a solid fecal layer. The length of the fat and solid layers are then measured using a magnifying lens.
acid steatocrit in percent =
= (fatty layer length in cm) / ((fatty layer length in cm) + (solid layer length)) * 100%
Amann et al found that for adults (minimum age 25) the spot stool acid steatocrit correlated with quantitative fecal fat analysis as:
fecal fat in grams per 24 hours =
= (0.45 * (acid steatocrit in percent as a whole number)) – 0.43
NOTE: In Figure 1 from Amann et al, the data over the steatocrit range of 0-31% looks like it should give a line comparable to the Guarino estimate (below). When the steatocrit is above 31% there is considerable scatter in the data, and it looks as if the true fat excretion is not well predicted by equation they give.
Interpretation:
• An acid steatocrit value < 31% was considered normal while a value >= 31% indicated steatorrhea.
• Van den Neucker used an acid steatocrit of > 10% as indicating steatorrhea.
Performance:
• Amann found that that the acid steatocrit was 100% sensitive and 95% specific with a positive predictive value of 90% for detection of steatorrhea when compared to the 72 hour method.
• Van dan Neucker found that the sensitivity was 75% and specificity was 84% for a spot collection
NOTE: It is important to distinguish the acid steatocrit from a nonacid steatocrit. An acid steatocrit will extract more fat from stool than a nonacid method will (personal communication. Dr Weldon Chiu in Zealand).
