Dipstick analysis of urine chemistry: benefits and limitations of dry chemistry-based assays

Urinalysis is a commonly utilized laboratory test, and analysis of urine has been studied and used since ancient times. Urine contains a wide array of metabolites that can provide information regarding the current physiologic state of the body and clinical manifestations of disease. In this review, we discuss the mechanics of the dry chemistry component of the urine dipstick such as the reaction principles underlying various assays and potential effects of collection and storage on results. Additionally, we discuss the benefits and limitations of the urine dipstick as it pertains to its use as a low-cost tool in point-of-care settings and the reasoning for a lack of its use as a broad screening tool.

[The significance of detection of nitrites in oral fluid of healthy people.]

The nitric oxide is a signal molecule in human organism characterized by a wide spectrum of biological effects. The exogenous nitric oxide is formed from food nitrates received with such green leafy vegetables as spinach, parsley, sorrel and also beet, cucumbers and tomatoes. The bacteria in oral cavity metabolize received with food nitrates up to nitrites. The nitrites as some intermediate metabolites of nitric oxide sufficiently exact reflect concentration of nitric oxide. The purpose of study is to examine analytical dependence and efficiency of express-device for detecting nitrites in saliva. The article presents the results of confirmation of testsystem for half-quantitative detection of content of nitrites in saliva. The device represents a hollow tube with a sensorial element within functioning by the principle of "dry chemistry". The concentration of nitrites in oral cavity was measured in 100 healthy people of both genders aged from 16 to 45 years. In case of consuming vegetables every day or 3-5 times a week higher levels of nitrite-anions (14,9-15,7 mg/l) are registered than in case of consuming vegetables and juices 1-2 times a week and rarely (9,9 mg/l). The concentrations of nitrites in saliva both in cases of regular training and low-activity life-style are within the limits of standards (11,9-14,9 mg/l). The average level of nitrites in saliva of participants of experiment with normal pressure made up to 16.5 mg/l that is significantly higher than in individuals from groups with increased and decreased arterial pressure (10,2 and 10,4 mg/l correspondingly).

Analytic and quality control validation and assessment of field performance of a point-of-care chemistry analyzer for use in the White rhinoceros

BACKGROUND

A chemistry point-of-care analyzer would be useful for evaluating injured wildlife, particularly White rhinoceros (Ceratotherium simum) that survive poaching attempts. The IDEXX VetTest could be suitable, but species-specific validation, development of a statistical quality control (QC) strategy, and evaluation under field conditions are necessary.

OBJECTIVES

The objectives were to (1) validate the VetTest for the White rhinoceros, (2) perform QC validation on the VetTest and generate a statistical QC strategy, and (3) apply this QC strategy to monitor performance under typical field conditions.

METHODS

Differences between White rhinoceros heparin plasma and serum, short-term imprecision, and reportable range using rhinoceros plasma and long-term imprecision using commercial quality control material (QCM) were assessed against prescribed total allowable error (TE_a ) for up to 15 analytes. Quality control validation was performed using data from the long-term imprecision study and TE_a . A QC strategy using QCM was developed and used to monitor performance under field conditions.

RESULTS

Imprecision was acceptable for all analytes except for ALP, ALT, and AST at low activities. The reportable range for AST and LDH differed from the manufacturer's specifications. Eleven analytes were suitable for statistical QC using the 1_3s rule, 3 using the 2_s rule; ALP was not suitable. In the field, observed error was < TE_a for all 15 analytes and the sigma metric was > 3.0 for 12 analytes.

CONCLUSIONS

The VetTest is suitable for use in the White rhinoceros. Statistical QC is possible for most analytes and useful for evaluation of field performance.

[The development of express-test for semiquantitative detection of thiocyanate ions in saliva.]

The article presents the results of approbation of the express test-system for semi-quantitative detection of content of thiocyanate ions in saliva as markers of tobacco smoking. The device corresponds to hollow tube with sensory element inside functioning on the principle of "dry chemistry". At saliva intake, the analyzing component (thiocyanate ion) interacts with reagents of sensory element with formation of colored thiocyanate complex. The intensity of color of formed complex permits to judge about content of thiocyanates in saliva by comparison with standard scale. The concentration of of thiocyanate ions in oral fluid of 100 health people of both genders aged from 16 to 45 years was analyzed. The questionnaire survey of respondents was carried out to establish smoking and non-smoking contingents. The analysis established that 30% were active tobacco smokers. The everyday smokers made up to 50% out of them, non-regular smokers (several cigarettes per week or month) - 50%. The reliable relationship between intensity of smoking and concentration of thiocyanate ions in saliva is established. The level of thiocyanate ions in saliva is significantly higher (2.5 mmol/l) in the group of everyday smokers than in saliva of non-smokers of periodically using tobacco articles (0.3-0.5 mmol/l) The increased concentrations of thiocyanate ions in saliva (≥ 1,5 mmol/l) were established in 7% of nonsmokers and are possible related to consumtion of food containing glucosinolates. The test is efficient for detecting smokers using from 1 to 10 cigarettes per day. However, it is of no use in case of sporadic type of smoking.

A homogeneous HLA-B*27 genotyping assay using dried reagent mixtures

The presence of HLA-B*27 allele with patients suspected with ankylosing spondylitis can be used in the diagnostic process. We have developed an assay for typing for the HLA-B*27 in whole blood dried on sample collection cards using pre-dried reagent wells and homogeneous time-resolved fluorescence based PCR approach. Essentially only the sample needs to be added to the dry ready-to-use reaction well in order to start the homogenous amplification assay. The method was validated with 229 samples also typed with an existing DELFIA-based method and results of both assays were 100% concordant. The dried reagents were shown to be stable at least up to eight weeks at room temperature without any decline in their performance.

Deproteinization of serum: another best approach to eliminate all forms of bilirubin interference on serum creatinine by the kinetic Jaffe reaction

The negative interference of conjugated, unconjugated, and delta bilirubin on patient serum creatinine determined by the kinetic Jaffe reaction is the unresolved problem. We compared bilirubin interference on thirty patients' serum creatinine obtained from four analyzers, with and without deprotenization before the Jaffe reaction, to the Vitros dry enzymatic method. We found significant negative interference from bilirubin on serum creatinine in all samples directly applied to four wet chemical methods, except the one incorporated with serum blank rate. The negative interferences linearly related to bilirubin concentration. However, bilirubin did not interfere on serum creatinine obtained from all wet chemical methods incorporated with deproteinization process before the reaction. We conclude that deproteinized serum before the reaction is the best approach to eliminate all forms of bilirubin interference on serum creatinine determined by the kinetic Jaffe reaction.

Novel assay for measuring serum conjugated bilirubin and its clinical relevance

We have developed a new enzymatic assay for the determination of conjugated bilirubin (Bc) using stable liquid reagents. In this assay, only Bc is selectively oxidized by bilirubin oxidase at pH 5. 0 in the presence of nitrilotris (methylenephosphonic acid) trisodium salt, ethylenediaminetetraacetic acid disodium manganese (II) salt, and 4-hydroxy-2,2,6,6,-tetramethylpiperidine 1-oxyl. Bc is quantitatively determined from a decrease in the absorbance at 450 nm caused by Bc oxidization. The reagent solutions of the assay were developed so that they could be stably stored for one year together with bilirubin oxidase, in order to eliminate the need to prepare working solutions every time they are required. The assay has good reactivity, differentiability, measurability, and precision. Neither ascorbic acid nor hemoglobin interfered with the measurement. Bc values determined by the assay reflected more clearly the pathophysiological condition of hepatobiliary disease patients with jaundice than the values of total bilirubin or direct bilirubin determined by conventional methods. From these observations, we concluded that this Bc assay is valuable for the evaluation of jaundice.