Urinalysis/chemical

Commonly, urine is qualitatively measured for protein, glucose, haemoglobin, ketone bodies and bile dyes. These components are usually found in the urine of healthy persons, but in such small quantities that they cannot be demonstrated by conventional tests. Under various pathological conditions, their concentration in the urine increases.

Test (diagnostic) strips
The detection of pathological urine components at the bedside or in the line of first contact with the patient is possible by means of test strips.

Test strips consist of a plastic carrier on which one or more indication zones are fixed. They are produced by aspirating a liquid analytical reagent into a suitable material (e.g. special filter paper) and gently drying it.

Diagnostic strips are available as mono-functional, poly-functional' or special examination strips.

Monofunctional strips contain basic indication zones for the semi-quantitative determination of a substance in urine. Polyfunctional strips consist of several indication zones, allowing the examination of several biochemical parameters at the same time. They are intended for cases where it is necessary to obtain as much information as possible about the patient's health status, e.g. during various screening events. In addition to monofunctional and polyfunctional strips, there are special test strips, which include combinations of two or more indication zones that are selected for the investigation of a specific disease, e.g. diabetes mellitus screening strips include a zone for the determination of glucose, ketone bodies, protein and pH.

With the help of test strips, the following parameters can be determined in the urine:
 * protein;
 * glucose;
 * ketolates;
 * bilirubin;
 * urobilinogen;
 * hemoglobin, erythrocytes;
 * ascorbic acid;
 * leukocytes;
 * nitrites;
 * pH;
 * density.

Glucose
Glucosuria is most often accompanied by a rise in glucose above the so-called renal glucose threshold (around 10 mmol/l). Glucose, which is normally filtered through the glomerular membrane, is in such high concentration in the primitive urine that it is not enough to be resorbed in the tubules and enters the final urine. Glucosuria with normal glycaemia is indicative of a defect in tubular transport mechanisms - we speak of renal glucosuria.

Urinary ketone bodies
See also Ketone bodies in urine.

Density
Urinary density is estimated indirectly by the concentration of cations using diagnostic strips. The indicator zone of the strip contains a suitable polyelectrolyte as an ion exchanger and the acid-base indicator bromthymol blue. The principle of diagnostic strips is based on the exchange of cations from urine, especially Na+, K+, NH4+, for H+ ions of the polyelectrolyte in the indication zone. The released H+ acidifies the weakly buffered acid-base indicator, which is in alkaline form. Acidification is accompanied by a change in colour to bromothymol blue. The disadvantage is that the diagnostic strip test does not take into account substances of a non-electrolyte nature such as glucose, proteins, urea, creatinine and some others.

Diagnostic strip test procedure
Remove only as many strips from the tube as you will need immediately. Immediately seal the tube with the remaining strips to protect the unused strips from moisture. Do not touch the indicator zone of the strips with your hands. Store the strips only in their original packaging and well sealed with a bag of desiccant, in a dark, dry place at a temperature of +2 to +30 °C.

Dip the strip briefly into the urine for 1-2 s so that all zones are wetted. Then remove the strip and remove the excess urine by wiping the edge of the strip on the rim of the container. Then place it in a horizontal position to prevent mixing of reagents from the individual reagent plates. After the prescribed reaction time, usually 60 s and 120 s for leucocytes, evaluate.

The assessment of the staining of the reaction zones of the diagnostic strips is carried out:
 * subjective comparison of the resulting colour with the colour scale on the label of the tube in which the strips are stored;
 * objectively' by reflection photometers, which measure the intensity of light of the appropriate wavelength reflected from the reaction field.