For the quality of the urinalysis and the associated diagnostic status, it is extremely important to use suitable measuring equipment.
This includes containers (cups, urine collection containers, catheters or bags), test materials (strips, indicator material) and analytical devices (analysis systems for urine test strips, microscopy technology, fluorescence flow cytometry and much more)
The utensils must be stored professionally and should only be used by trained personnel. For example, cups may already be contaminated with bacteria and germs due to improper storage, or some indicator fields of the strips may already be oxidized by contact with air and moisture.
There are various studies that question the reliability of conventional urine tests. However, it is not always clear to what extent the human factor or rather the test equipment is responsible.
For example, Meyer et al. in 1994, carried out a retrospective study of 300 urine samples from hypertensive pregnant women and reported that 66% of the women with a negative or partial negative result had significant proteinuria. The false positive rate was 26%.
Halligan et al. had a similarly high false-negative rate (66%) in 500 samples of hypertensive pregnant women.
In a prospective study from 1995, Brown and Buddle found that test strips produce false-negative values between 8-18%, at a very high false-positive rate of 67%.
Despite the high discrepancies, which are probably due to different test strips, these studies strongly question the diagnosis of test strips in a proteinuria during pregnancy. False positive results can lead to an overexamination, while false negative results can put women and their children in great danger.
There are several reasons for such disagreements, including observer errors, the characteristics of the semi-quantitative test strip, the units of protein estimation, the urine samples used and the biochemical methods to which the tests are based.
Due to the many discrepancies in the accuracy of test strips, especially with regard to the determination of urinary tract infections, Deville et. Al. carried out a meta-study to shed more light on the subject (leukocytes, nitrite). Result: Test strips are useful to rule out the presence of an infection. But only if the results of both values, nitrite and leukocytes are negative. The sensitivity of the combination of both tests varies between 68% and 88%. Positive results should be confirmed further.
In Graff’s textbook of routine urinalysis and body fluids, a kind of bible for urinalysis, the various susceptibility to the indications are partly listed by manufacturer. One result of the susceptibility of the test strips to errors is the need to consider at least two parameters for most indications (urinary tract infection: leukocytes / nitrite, kidney disease: albumin / creatinine, proteinuria: protein / spec.density). To avoid diagnostic errors due to false-positive, and more importantly false-negative results.
In principle, appropriate utensils and sufficient knowledge should always be taken into account during the analysis by the person performing the system. If there is any doubt about the results, a more in-depth investigation should always be carried out.
