Urine test strips and POCT

Urine Test Strips

Click on the links to navigate this page
Introduction	Correct timing of colour development
General information	Correct colour interpretation
Correct specimen collection	Correct sample disposal
Patient and operator identification	Limitations of procedure
Correct technique	Quality Control

Competency documents, both paper and electronic are available for those wishing to update their records. A Competency is also available for Clinitek 50 urine reflectance meters.

Introduction

The CDHB uses two types of urine dipstick, the Roche L Combur-7 and the Bayer Multistix 8. Most wards use L Combur-7 strips. Those using Bayer Clinitek 50 reflectance meters for their urine testing must use the Multistix 8 strips.

Combur-7 strips are available from the Christchurch Pharmacy.

See the chart below for the list of components of each type- (Y= tests available; N= not).

Component	Roche L Combur-7	Bayer Multi-Stix 8
pH	Y	Y
protein	Y	Y
glucose	Y	Y
ketones	Y	Y
blood (rbc)	Y	Y
nitrite	Y	Y
leucocytes (wbc)	Y	Y
specific gravity (SG)	N	Y
urobilinogen	N	N
bilirubin	N	N

General information

IMPORTANT: PROTECTION AGAINST AMBIENT MOISTURE, LIGHT AND HEAT IS ESSENTIAL TO GUARD AGAINST ALTERED REAGENT REACTIVITY.
Always keep reagent test strips in the bottle with the cap tightly closed.
Do not remove the strip from the bottle until immediately before it is to be used for testing. Replace cap immediately and tightly after removing the reagent test strip.
The recommended lowest actionable reading for blood and protein is trace. If repeat is negative, no further action required. If repeat is positive for protein, a 24 hour urine protein plus MSU for C&S and microscopy is recommended; if repeat is positive for blood, MSU for C&S and microscopy is recommended.
If glucose is positive, patient should be investigated for possible diabetes.
Positive nitrite/leucocytes should be followed up by MSU for C&S and microscopy. Note that a negative nitrite test does not always mean the absence of a UTI. Nitrite testing is positive only in the presence of gram negative bacteria, not gram positive.
Other points to note are that FRESH urine must be used, and that dip-sticks will not detect Bence Jones Protein.

Correct specimen collection

Collect urine in a clean container and test it as soon as possible.
Do not centrifuge.
The use of urine preservatives is not recommended.
If testing cannot be done within 60 minutes, place urine in refrigerator. Let it return to room temperature and mix it well before testing.
Nitrite testing is best performed on an early morning specimen which has been in the bladder for at least 4 hours before voiding.
If urine is to be tested for bilirubin or urobilinogen, keep specimen in dark as these compounds degrade in the presence of light.
Prolonged exposure of urine to ambient temperature may enhance microbial growth, resulting in altered pH, lowered urine glucose and false positive blood reactions due to production of bacterial peroxidases.
Contamination of urine with skin cleansers may lead to erroneous results.

Patient and operator identification

Patients must be correctly identified with a minimum of 2 points of ID- preferably name and national patient number. Temporary admission ID and date of birth are also satisfactory.

The staff member performing the measurement must also be identified. Ensure that all printouts or transcriptions are signed clearly and dated.

Correct strip immersion time and technique

This is very important- too little or incomplete immersion will cause insufficient penetration of urine into the test strip. This will result in a possible false negative result.

Too long an immersion time will result in elution or washing out of the test strip reagent colour, resulting in a pale reaction or falsely low result.

Read the instructions carefully- The general rules are:

Collect FRESH urine in a clean dry container.
Remove one strip and immediately replace the lid tightly.
Briefly (no longer than 1 second) dip the whole of the reaction area of the strip into the urine.
Wipe the side edge of the test strip along the edge of the vessel to remove excess urine.
After the appropriate time (usually 60 seconds, but time may vary for same components), in a good light such as fluorescent, compare the colour reaction with the colour charts on the label.
Lay the urine test strip alongside the colour charts. Avoid laying the strip directly on the colour charts as this will result in the urine soiling the chart.

Correct timing of each component colour development

As noted above, correct timing is very important. Too little time to read may result in false negative readings; too much delay in reading time may result in false positives.

For the Combur-7 strips, read all colours at 60 seconds.

For the Multistix 8, read the glucose at 30 seconds; the specific gravity at 45 seconds; the pH, protein, blood and nitrite at 60 seconds and the leucocytes at 2 minutes.

Any colour changes that occur after 2 minutes are of no consequence.

Correct colour interpretation

Always compare the reagent strip colours side by side with the colour scales on the label, in a good light, e.g., fluorescent light. Do not read the strips in direct sunlight.

If the strips are read on an instrument, e.g., a urine test strip reflectance meter, always follow the instructions in the appropriate operator's manual.

(An interesting note: In the last 12 months or so during their laboratory inspections, the American accreditation authorities, (CLIA, JCAHO and CAP) have focused on colour blindness testing of all POCT operators throughout the US.)

Correct sample disposal

Always dispose of samples and contaminated consumables in a recommended waste disposal container. This should be in accordance with recommended CDHB Infection Control and Health and Safety guidelines.

Limitations of procedure

Here is a very interesting journal article detailing errors resulting from human versus reflectance meter colour interpretation: "Error Rates" using different reading methods. (This is a Word document. Use the Back button on your browser to return here once you have finished reading the article).

Many of the problems associated with manual colour interpretation and timing of the readings can be overcome by the use of a test strip reader. The one in use in several locations within the CDHB is the Clinitek 50 reflectance meter.

Problems associated with each component

Glucose

Reactivity diminished with high ascorbic acid levels (>50 mmol/L)
Reactivity diminished as Specific Gravity of urine increases.
Reactivity may vary with temperature.

Ketone

False positives may occur in highly pigmented urine, e.g., raised urine bilirubin.

Specific Gravity (S.G.)

Highly alkaline urines may cause low readings.
Moderate increases of urine protein (1-7.5 g/L) may elevate S.G.

Blood

Elevated S.G. may reduce reactivity of blood.
Captopril will cause decreased reactivity.
Hypochlorite contaminant may produce false positive results.
Microbial peroxidase associated with UTI may cause a false positive.

If proper procedure is not followed and excess urine is left on the strip, contamination of the urine combined with the acid protein reagent may lower the pH.

Protein

False positives with highly buffered or alkaline urines may result.
Contamination of urine sample with quaternary ammonium products or skin cleanser containing chlorhexidine may result in false positive results.

Nitrite

Pink spots or pink edges should not be interpreted as a positive reaction.
Colour development is not proportional to the number of bacteria present.
A negative result does not mean that bacteria are not present. A UTI caused by non-nitrite producing bacteria may still be present.
High S.G. may reduce nitrite colour formation.

White cells (leucocytes)

Elevated urine glucose (>160 mmol/L) or high S.G. may cause decreased results.
Presence of Keflin, Keflex or high concentration of oxalic acid may decrease results.
High levels of tetracycline may cause a false negative.

Quality Control

The performance of reagent test strips should be monitored regularly, say once per week, with known negative and positive samples or a quality control (QC) test.

An example is the Bayer CHEK-STIX^® quality control solution. This is purchased by the lab as a vial of special QC dry strips. Each QC strip is soaked in 12 mL of distilled or deionised water for 30 minutes. The dyes from the QC strip leach out into the water. The QC strip is then discarded and the solution is mixed well. This gives a "urine" of known values. The solution is stable for 7 days at 4 degrees Celsius. It may also be aliquoted and frozen.

In fact, all Clinitek 50 users are supplied with frozen aliquots of made up solution. A fresh vial is thawed, mixed and analysed daily or as required. Results are monitored and written on the QC charts provided.

This solution is analysed using a regular urine test strip in an identical manner to a patient's sample. The printout values should fall within predetermined areas on the CHEK-STIX control chart as supplied by the POCT Coordinator. The correct colour match is proof that the test strips are still working satisfactorily. Only if the QC results are correct, are patients' samples analysed.

This free service is provided by the laboratory to all Clinitek 50 users.

Canterbury Health Laboratories recommends to all users of urine test strips that they regularly check their operators, test strips and procedure.

For more information, please contact the POCT Coordinator.