Clinical Chemistry, Vol 18, 150-154, Copyright © 1972 by the American Association for Clinical Chemistry

Instrumental and Procedural Sources of Error in Determination of Bile Pigments in Amniotic Fluid

¹ Clinical Chemistry Laboratory, Hartford Hospital, Hartford, Conn. 06115.

Although the Liley spectrophotometric estimation of bile pigments in amniotic fluid [Amer. J. Obstet. Gynecol. 82, 1359 ( 1961)] is widely used, the levels of accuracy and precision necessary for clinically meaningful results have not been clarified. This paper delineates some of the important instrumental and procedural sources of error, and how each affects the final value of A₄₅₅: (a) A limit of error propagation is presented to show that the uncertainty in A₄₅₅ due to instrumental factors is considerably larger than is commonly appreciated. (b) It is desirable to use a logarithmic baseline estimation, as did Liley, instead of a linear estimation, which can introduce a serious bias. (c) Failure to establish a true zero-absorbance baseline before scanning the specimen can also result in a significant bias in the calculated A₄₅₅.

Submitted on October 1, 1971
Accepted on October 26, 1971