Evaluation of Aqueous Humor as a Surrogate for Serum Biochemistry in California Sea Lions (<I>Zalophus californianus</I>)

Abstract

The aim of this study was to evaluate the use of post mortem aqueous humor analysis in estimating serum chemistry in California sea lions (Zalophus californianus). Serum and aqueous humor from the left eye were collected from 35 sea lions that were euthanized due to poor prognosis. Each animal was examined post mortem, and each head was preserved at ambient temperature. Aqueous humor was collected from the right eye either 24 or 48 h after death. All samples were analyzed with an automated chemistry analyzer by bichromatic photometry and potentiometry. Blood urea nitrogen, creatinine, sodium, chloride, and magnesium showed significant positive linear relationships between serum and aqueous humor values both at the time of death and 24 h later. For aqueous humor sampled after 48 h, the relationships were only significant for blood urea nitrogen and creatinine. For the remaining chemistry parameters, the relationship between levels of those from serum and in aqueous humor were not significant. Serum and aqueous humor collected from 15 animals diagnosed with renal failure were evaluated for antibodies to Leptospira using the microscopic agglutination test. All tested sera were positive for L. interrogans serovar pomona, with titers greater than 1:25,600. Of titers tested in the aqueous humor, 56% were positive, having values of 1:200 to 1:12,800. These results indicate that an accurate estimate of serum blood urea nitrogen and creatinine can be made from the analysis of aqueous humor at necropsy of California sea lions within 48 h of death, facilitating the diagnosis of renal failure in beached carcasses (one of the most common causes of death in wild sea lions).