Automated enzymatic method for measuring oxalate in urine.

1076 CLINICALCHEMISTRY, Vol. 33, No. 6, 1987 second, there was a large paraprotein band at 29 gIL in the beta region, which was determined to be an 1gM-kappa by immunofixation electrophoresis. To determine whether the presence of the paraprotein or an unusual property of this patient’s albumin was responsible for the inability to quantil albumin by bromcresol green binding, I isolated the patient’s albumin by affinity chromatography on Cibacron Blue-Sepharose and the 1gM fraction by chromatography on DEAE-cellulose and G-150Sephadex. The patient’s isolated albumin showed normal ability to react with bromeresol green. When the isolated 1gM paraprotein was added to the patient’s albumin or to any other serum sample, the albumin concentration was underestimated in proportion to the amount of 1gM added. The kinetics of the reaction of bromcresol green and albumin were monitored in normal serum and in the patient’s serum. Albumin normally reacts rapidly with bromcresol green, and color development is complete in <5 5. The presence of the 1gM paraprotein in this patient’s serum delayed the reaction such that color development required several minutes to reach its final value. Since the Astra Ideal reads absorbance at 10 s and computes albumin concentration as if the reaction were complete, albumin concentration was significantly underestimated. To determine whether the 1gM was an antialbumin, and hence was interfering competitively with the dye, I iminobilized albumin and the 1gM on agarose (Sepharose), and prepared affinity columns with these (1). The 1gM column (12 mg of 1gM per 5 mL of Sepharose) demonstrated no affinity for 2 mg of albumin, and the albumin column (120 mg of albumin per 20 mL of Sepharose) demonstrated no affinity for 14 mg of the 1gM. Evidently the interaction between albumin and the 1gM that interferes with the bromcresol green binding is not a specific antibody-antigen interaction. To determine whether other 1gM paraproteins might also slow the reaction of albumin with bromcresol green, I studied 15 additional serum samples containing 1gM paraproteins in concentrations ranging from 0.4 to 10 gIL. None showed any evidence of a slowed reaction between albumin and bromcresol green, all reaching final color development within 5 s. The suppression of reaction between albumin and bromcresol green that occurred in the presence of this 1gM paraprotein does not appear to be a common phenomenon for 1gM paraproteins but an isolated property ofthe specific 1gM described.