Urine Dipstick Test

Reading The Dipstick
The dipstick yields valuable information which is available by direct observation of the coloured patches on the test strip (dipstick) after brief immersion in the urine specimen. There are a number of parameters which are determined: pH, specific gravity (S.G.), protein, glucose, ketones, nitrite and leukocyte esterase.

Acid/Base (pH)
The dipstick yields the pH, a reflection of acid/base levels. The initial filtrate of blood plasma is usually acidified by the renal tubules and collecting ducts (microscopic structures in the kidneys of which there are millions) from a pH of 7.4 to about 6 in the final urine. in other words, the urine is acidified. However, depending on the acid-base status, urinary pH may range from as low as 4.5 to as high as 8.0. One task nature has assigned to the kidneys is to rid the body of acid.

Specific Gravity (S.G.)
Specific gravity measures urine density which reflects the ability of the kidney to concentrate or dilute the urine relative to the plasma from which it is filtered. Although dipsticks are available that also measure specific gravity in approximations, most laboratories measure specific gravity with a instrument call a refractometer. Specific gravity between 1.002 and 1.035 on a random sample should be considered normal if kidney function is normal. Any measurement below 1.007 to 1.010 indicates hydration and any measurement above it indicates relative dehydration. Urine having a specific gravity over 1.035 is either contaminated, contains very high levels of glucose, or the patient may have recently received high density radiopaque dyes intravenously for radiographic studies or low molecular weight dextran solutions.

Protein
While the dipstick test has a portein measurement, more elaborate tests for urine protein should be performed since cells suspended in normal urine can produce a false high estimation of protein. Normal total protein excretion does not usually exceed 150 mg/24 hours or 10 mg/100 ml in any single specimen. More than 150 mg/day is considered proteinuria. Proteinuria greater than 3.5 gm/24 hours is severe and indicates the nephrotic syndrome. Dipsticks detect protein by production of color with an indicator dye, Bromphenol blue, which is most sensitive to albumin but detects globulins and Bence-Jones protein poorly. Precipitation by heat is a better semiquantitative method, but overall, it is not a highly sensitive test. The sulfosalicylic acid test is a more sensitive precipitation test. It can detect albumin, globulins, and Bence-Jones protein at low concentrations. "Trace" protein is equivalent to 10 mg/100 ml or about 150 mg/24 hours (the upper limit of normal). 1+ corresponds to about 200-500 mg/24 hours; 2+ to 0.5-1.5 gm/24 hours, a 3+ to 2-5 gm/24 hours, and a 4+ represents 7 gm/24 hours or greater.

Glucose
Glycosuria (excess sugar in urine) generally means diabetes mellitus.

Ketones
Ketones (acetone, aceotacetic acid, beta-hydroxybutyric acid) may be present in diabetic ketosis or other forms of calorie deprivation (e.g. starvation). Ketones are easily detected using either dipsticks or test tablets containing sodium nitroprusside.

Nitrite
A positive nitrite test indicates that bacteria may be present in significant numbers. Gram negative rods such as E. coli are more likely to give a positive test.

Leukocyte Esterase
A positive leukocyte esterase test results from the presence of white blood cells either as whole cells or as destroyed cells. A negative leukocyte esterase test means that an infection is unlikely. Without additional evidence there is no need for culture.

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