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y reflectance photometry provide an alternative to the
color chart and offer better precision and standardization.Bilirubin/Urobilinogen
Hemoglobin degradation ultimately results in the for?mation of the waste product bilirubin, which is then
converted to urobilinogen in the gut through bacterial
action.A gram-posi?tive pathogen, such as Staphylococcus, Enterococcus, or
Streptococcus, may not produce nitrate-reducing enzymes;
alternatively, a spot urine sample may not have been
retained in the bladder long enough to pick up a sufficient
number of organisms to register on the reagent strip.16
Leukocyte Esterase
White blood cells (WBCs), especially phagocytes, con?tain esterases.Dipstick methods for uro?bilinogen differ, but most rely on a modification of the
Ehrlich reaction with p-dimethylaminobenzaldehyde.16
Hemoglobin/Blood
Intact or lysed RBCs produce a positive dipstick result.Nitrite
This assay semiquantitates the amount of urinary reduc?tion of nitrate (on the reagent strip pad) to nitrite by the
enzymes of gram-negative bacteria.The analytes routinely
tested are glucose, protein, ketones, nitrite, leukocyte
esterase, bilirubin/urobilinogen, and hemoglobin/blood.In conditions
of prehepatic, hepatic, and posthepatic jaundice, how?ever, urine dipstick tests for urobilinogen and bilirubin
may be positive or negative, depending on the nature of
the patient's jaundice.Positive
dipstick results should be confirmed by more specific
chemical assays, as described in Chapter 11, or more
commonly by microscopic evaluation to detect casts.Abnormal results are followed up by specific quantita?tive or confirmatory urine assays.Protein
Reagent strips for UA are used as a general qualitative
screen for proteinuria.They are primarily specific for
albumin, but they may give false-positive results in
specimens that are alkaline and highly buffered.Glucose and Ketones
These constituents are normally absent in urine.A positive dipstick for esterases indicates
possible WBCs in urine.Although most of this urobilinogen is excreted as
urobilin in the feces, some is excreted in urine as a color?less waste product.A more in-depth view of bilirubin
metabolism and assay methods is given in Chapter 25.The dipstick will be positive in cases of renal trauma/
injury, infection, and obstruction that result from calculi
or neoplasms.The
clinical significance of these analytes and their testing
methods are discussed in Chapter 14.Reagent strip tests for bilirubin involve diazotization and
formation of a color change.This amount is normally too small to
be detected as a positive dipstick reaction.A negative result does
not mean that no bacteriuria is present.