gators concluded that the reagent strip the refractometer read 1.003 when the refractometer The various reasons for osmotic di-
arrheas include malabsorption, lactose Ampicillin Interference with Test for
read >1.003. Thus in using the two
specific gravity methods to evaluate intolerance, or an infection that results SulfiteOxldaseDeficiency
results relating to dilution tests, there in rapid passage of gastric and small-
was agreement in 20% of the cases and bowel contents to the colon. Reasons for To the Editor:
disagreement in 80% of the cases in non-osmotic diarrheas also are varied A recent Letter from Summerville
this study. and may include effects of bacterial and colleagues (1) concerns the useful-
2. “...[specific gravity] of urines toxins (as in some E. coli enteritis), of ness of the iodine-azide spot test in
after fluid restriction (concentration hormones secreted by ectopic tumors, or screening for sulfite oxidase (EC
tests) should be 1.022 or higher.. Of .“ of drugs (e.g., some prostaglandins, 1.8.3.1) deficiency. We have found that
the 133 cases in the present study, castor oil). urine specimens containing the fre-
there were 32 cases of urines where at When a watery diarrhea is present, quently prescribed antibiotic ampicil-
least one result was 1.022. Of these, the measured osmolality of stool water lin often gave a falsely positive reac-
10 (31%) patients had both results and that calculated from its sodium and tion, making interpretation of the posi-
1.022, 14 (44%) showed a result less potassium concentrations (taken as tive spot test result difficult. Our
than 1.022 when the refractometer twice the sum of the two) can be com- laboratory now uses a simple spectro-
read 1.022, and eight (25%) had a pared. A large deficit in the calculated photometric method for thiosulfate (2)
result for specific gravity 1.022 when osmolality indicates osmotic diarrhea; as a screening test for sulfite oxidase
CLINICAL CHEMISTRY, Vol. 29, No. 1, 1983 211