6.0 solutions(Table1). Table 1. ResultsObtainedfor ... - Clinical Chemistry

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of barbiturates and neutral drugs (3). 0.85. Phenobarbital may also be determined. 0.85 by our EMIT technique (4). Primidone. 0.89 analysis is rarely requested.
ing procedure for sulfite-oxidase deficiency (4). This test utilizes the ability of the thiosulfate anion, S2032, to catalyze the reduction of zero-valent iodine by the azide anion (5). A positive test requires immediate decolorization of the iodine-azide reagent solution (12 - 21-), accompanied by vigorous bubble formation (N -. 3/2N2). The use of this procedure in one case of sulfite-oxidase deficiency (2) gave

Table 1. ResultsObtainedfor the lodine-AzideSpotTest with AqueousSolutionsof Thiosulfate mmol/L

the iodine-aside reagent required thiosulfate concentrations of about 6 mmol/L; at lower concentrations, bubbling was less vigorous and decolorization proceeded less rapidly. At concentrations of about 1 mmolfL, decolorization proceeded almost entirely to completion, but in general required swirling of the reacting solutions. With

thiosulfate concentrations oflessthan 0.5 mmolfL, little or no decolorization occurred; there was, however, slow evolution of nitrogen. Parallel results were obtained when thiosulfate was added to

Vigorous bubbling, decolorization complete

3.4

Vigorous bubbling, decolorization

complete

in 15s. Slow bubbling, complete

1.7

1.1

Slow decolorization,

may not yield an unequivocable

deficiency positive

reaction according to the criterion

of

of swirling the reaction mixture.

0.9

To the Editor:

Slow decolorization, bubbling; solution would not fully decolorize. Very faint decolorization, slow bubbling.

0.5

“High-performance” liquid chromatography (HPLC) is a commonly used technique for drug analysis in the clinical chemistry laboratory. Although it has simplified the simultaneous determination of various drugs possible, the

long retention times have been a drawback in routine work because sample have been shown to be extremely sensithroughput is slow. The commercially tive to dietary intakeofsulfur-contain- available High-Speed C18-system Corp., Norwalk, CT ing amino acids (2,3). As a result, chil- (Perkin-Elmer then with sulfite-oxidase deficiency for 06856) was found very promising and whom feeding is a problem, or whose considerablyshortenedthe time for parents have learned to avoid certain chromatography. foods high in sulfur content, may be Our previously reported method for missed in the screening procedure if the determination of anticonvulsant drugs positive/negative cutoff level is set too (1) was modified and applied to this high. system as follows: Until further data regarding urinary An HPLC pump model 440 (Waters thiosulfate concentrations are available Associates, Milford, MA 01757) and an LC-85 spectrophotometric detector from both normal and sulfite-oxidase (Perkin-Elmer) were used. The detector deficient populations, further workup, was set to the “fast response” mode and such as determination of S-sulfo-Lconcentrations

should be con-

References I. Mudd, S. H., Irreverre, F,, and Laster, L., Sulfite oxidase deficiency in man: Demonstration of the enzymatic defect. Science 156, 1599-1602 (1967). 2. Shih, V. E., Abroms, I. F., Johnson, J. L., et al., Sulfite-oxidase deficiency Biochemical and clinical investigations of a hereditary metabolic disorder in sulfur metabolism. N. Engl.J. Med. 297, 1022-1028 (1977). 3. Irreverre, F., Mudd, S. H., Heizer, W. D., et al., Sulfite-oxidase deficiency: Studies of a patient with mental retardation, dislocated ocular lenses, and abnormal urinary excretion of S-sulfo-L-cysteine, sulfite, and thiosulfate. Biochem. Med. 1, 187-217 (1967). 4. Shih,

V. E., Laboratory

the Detection

of Hereditary

Techniques

for

Metabolic

Dis-

orders. CRC Press, Cleveland, OH, 1977,p immediate decolorization. Further, 13 urine concentrations of thiosulfate in patients with sulfite-oxidase deficiency 5. Feigl, F., Spot Tests in Inorganic Analy718

Lab. Med. Ctr.

complete after >2 mm

sidered in any patient whose urine showed a significant decolorization reaction with the iodine-aside spot tests.

patient with sulfite-oxidase

Columbia-Presbyterian 622 W. 168th St. New York,NY10032

Analysisfor Carbamazepineand Phenytolnin Serumwith a HighSpeed LiquidChromatography System(Perkin-Elmer)

bubbling; decolorization complete or almost

cysteine

sidered positive. However, as has been shown in one case (2),the urine from a

University

New York,NY10032 1 Also at Special and Microchem.

decolorization requiring more than 1 mm.

observed, but occasionally samples showed slow evolution of nitrogen. In any realscreeningsituation, the

and limits of urine thiosulfate from either afflicted or normal populations are not defined. Thus it is difficult to decide what qualitative chemical result of the iodine-aside spot test should be con-

Dept. of Pathology Coll. Physicians & Surgeons

Columbia

in less than 2 s.

“normal” urine. When 50 “normal” urines were tested, no decolorization was

assignment of the test positive/negative cutoff value is complicated by overlap of test scores obtained from that population affected by the disorder and those groups (i.e., normals and biological false positives) not so affected. Unfortunately, scantdata from patients with sulfite-oxidase deficiency are available,

David A. Summerville Manju Shah Michael A. Pesce1

Reaction

6.0

NY, 1950, p

318.

Thiosuif ate,

results that were difficult to interpret, thusraising questionsastotheutility of this procedure as a screening test. As part of the recent evaluation of a pediatric patient with neurologic dysfunction, the sulfite-oxidase screening assay was requested. This gave us the opportunity to investigate some of the analytical variables and to interpret results obtained with the iodine-azide reaction. The iodine-aside reagent contains, per liter, 100 mmol of iodine, 241 mmol of potassium iodide, and 92 mmol of sodium aside. Place one drop of the test solution on a spot plate and add one drop of the iodine-aside reagent. Compare the results for the urine sample with resultsfor a seriesof aqueous thiosulfate solutions(Table1). Immediate decolorization (