A measure of the activity of the enzyme amylase in blood serum, defined in 1938 by Michael Somogyi.¹ Symbol, SU. It has also been used for the enzyme's activity in urine and plasma. Amylases break down starch into simpler compounds. In the Somogyi test, starch is added to the serum and after 30 minutes have passed the quantity of simpler compounds is checked. Of course, it is more complicated than that.
“Thus, when we say that the diastase value of a sample of blood plasma is 120, we mean that, under the standardized conditions described, 100 cc. of that plasma produce from starch cleavage, products which have the same copper-reducing power as 120 mg. of glucose.” [page 405]
Thus, 1 Somogyi unit is equivalent to 1 milligram per deciliter of amylase. The “diastase” of the 1930's has been replaced by the more specific alpha‑, beta‑ and gamma‑amylases; α‑amylase being the predominant one in humans.
Tests of blood amylase are most often done in diagnosing and treating pancreatitis. Generally a reading of more than 200 SU or less than 40 SU is of clinical concern. To convert Somogyi units to international units per liter, multiply by 1.85. (One international unit = 60 µKat)
The rise and gradual obsolesence of the Somogyi unit can be seen using Google's n-gram viewer. To check references, go to https://books.google.com/ngrams, enter Somogyi unit yourself, and click on the time period links shown at the bottom of the frame (we cannot embed those).
1. Michael Somogyi.
Micromethods for the estimation of diastase.
Journal of Biological Chemistry, vol 125, pages 399-414 (1938).
May be downloaded from www.jbc.org/
Modifications of two methods for the assay of amylase.
Clinical Chemistry, vol. 6 no. 1, pages 23-35 (February 1960).
May be downloaded from www.clinchem.org/content/6/1/23.short
Diastatic activity of human blood.
Archives of Internal Medicine (Chicago). vol 67, no. 3, pages 665-679.(March 1941).
An interesting article on the difficulties, in the period, of determining serum amylase. Apparently results still vary quite a bit depending on which lab does the testing.
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Last revised: 29 April 2014.