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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.

y reflectance photometry provide an alternative to the
color chart and offer better precision and standardization.
Abnormal results are followed up by specific quantita￾tive or confirmatory urine assays. The analytes routinely
tested are glucose, protein, ketones, nitrite, leukocyte
esterase, bilirubin/urobilinogen, and hemoglobin/blood.
Glucose and Ketones
These constituents are normally absent in urine. The
clinical significance of these analytes and their testing
methods are discussed in Chapter 14.
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. 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.
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. A negative result does
not mean that no bacteriuria is present. 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. A positive dipstick for esterases indicates
possible WBCs in urine.
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. Although most of this urobilinogen is excreted as
urobilin in the feces, some is excreted in urine as a color￾less waste product. This amount is normally too small to
be detected as a positive dipstick reaction. 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. A more in-depth view of bilirubin
metabolism and assay methods is given in Chapter 25.
Reagent strip tests for bilirubin involve diazotization and
formation of a color change. 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.
The dipstick will be positive in cases of renal trauma/
injury, infection, and obstruction that result from calculi
or neoplasms.