A quality control product for urinalysis

Detection of pyuria and bacteriuria in symptomatic ambulatory women

OBJECTIVE

To compare the abilities of two methods for rapid detection of pyuria and three methods of urinalysis to predict significant bacteriuria in symptomatic ambulatory women.

DESIGN

Prospective simultaneous comparison of the results of dipstick urinalysis, standard microscopic urinalysis, and hemocytometric cell counting and Gram staining with the results of a standard urine culture.

SETTING

Two outpatient ambulatory care facilities serving predominantly minority and uninsured individuals.

SELECTION CRITERIA

Nonpregnant women presenting with symptoms of urinary tract infection without symptoms of vaginal infection.

MEASUREMENTS AND MAIN RESULTS

105 women with symptoms were evaluated. The sensitivities of the dipstick urinalysis and the microscopic urinalysis in predicting pyuria as defined by hemocytometry were 0.76 and 0.77, respectively, and their specificities were 0.94 and 0.97, respectively. The sensitivities and specificities of the three methods of urinalysis in predicting greater than or equal to 10(4) colony-forming units (CFU)/mm3 in a urine culture were 0.88 and 0.70 for the leukocyte esterase-nitrite dipstick urinalysis, 0.98 and 0.68 for the standard microscopic urinalysis, and 1.00 and 0.49 for the Gram staining and hemocytometric cell counting.

CONCLUSIONS

The standard urinalysis was the most accurate single method to predict significant bacteriuria in symptomatic ambulatory women. Sequencing the dipstick urinalysis with the standard urinalysis may be a cost-effective approach to evaluating these patients in clinical practice.

Problems associated with clinical chemistry quality control materials

Quality control methods and materials are widely used to monitor each and every facet of clinical chemistry laboratory performance. Quality control materials are also used in evaluation of methods and as secondary standards. A wide range of liquid and lyophilized materials are available from commercial sources and are prepared in individual laboratories. Many problems arise in the use of quality control materials. Problems discussed in this review include the use of nonhuman based materials and additives of animal origin, the physical and chemical characteristics of quality control materials that differentiate such samples from those from patients, attempts to generate quality control materials with elevated levels of particular analytes, the difficulties in handling and storage of quality control materials, the dangers of hepatitis, and the stability of quality control materials both during storage in the laboratory and after their reconstitution. The advantages and disadvantages of liquid and lyophilized quality control materials are discussed. The assignation of analyte values is of particular importance as the current trend is to consider inaccuracy of laboratory methods in addition to imprecision. This review assesses relevant publications in an area of fundamental importance to quality control in clinical chemistry.