Pocket Guide to Diagnostic Tests-0838581358.pdf

32 Pocket Guide to Diagnostic Tests
TABLE 2–2 (CONT’D). COMPONENTS OF THE URINE DIPSTICK. 1
Lowest
Detectable
Test Values Range Comments
Blood
Nitrite
Leukocytes
(esterase)
O 2 0.015–
O
O 3
0.062 mg/dL
hemoglobin
0.06–0.1 mg/dL
nitrite ion
6–15 WBCs/hpf
Test equally sensitive to myoglobin and hemoglobin
(including both intact erythrocytes and
free hemoglobin). False-positive results can be
caused by oxidizing contaminants (hypochlorite)
and microbial peroxidase (urinary
tract infection). Test sensitivity is reduced in
urines with high specific gravity, captopril, or
heavy proteinuria.
Test depends on the conversion of nitrate
(derived from the diet) to nitrite by gramnegative
bacteria in urine. Test specific for
nitrite. False-negative readings can be caused
by ascorbic acid. Test sensitivity is reduced in
urines with high specific gravity.
Indicator of urinary tract infection. Test detects
esterases contained in granulocytic leukocytes.
Test sensitivity is reduced in urines with high
specific gravity, elevated glucose concentrations
(≥ 4 g/dL), or presence of cephalexin,
cephalothin, tetracycline, or high concentrations
of oxalate.
1 Package insert, revised 9/95. Bayer Diagnostics Reagent Strips for Urinalysis, Bayer Corporation.
2 Except in menstruating females.
3 Except in females with vaginitis.
Microscopic Examination
a. Examine the area under the coverslip under the low-power
and high-dry lenses for cells, casts, crystals, and bacteria. (If
a Gram stain is done, examine under the oil immersion lens.)
b. Cells may be red cells, white cells, squamous cells, transitional
(bladder) epithelial cells, or atypical (tumor) cells. Red
cells suggest upper or lower urinary tract infections (cystitis,
prostatitis, pyelonephritis), glomerulonephritis, collagen
vascular disease, trauma, renal calculi, tumors, drug reactions,
and structural abnormalities (polycystic kidneys).
White cells suggest inflammatory processes such as urinary
tract infection (most common), collagen vascular disease, or
interstitial nephritis. Red cell casts are considered pathognomonic
of glomerulonephritis; white cell casts, of pyelonephritis;
and fatty (lipid) casts, of nephrotic syndrome.