Laboratory Testing

Before trusting any laboratory value, one should always verify that the results actually stem from the patient and that laboratory or collection error has not occurred. Even in modern hospital systems, laboratory values are not completely reliable and blood or urine samples may have been exchanged. This is particularly important in episodes of mass casualty with numerous traumatized patients arriving simultaneously at the emergency room (ATLS Manual 2004b). In all cases, laboratory values that appear erroneous or do not make sense should be quickly rechecked before irrevocable steps are taken in the patient's care. Blood drawn from a vein above an intravenous infusion, for example, may show a very low hematocrit level indicating massive blood loss, but if the patient appears well and has normal vital signs the value might best be rechecked rapidly before acting.

In the management of emergencies, the time required for a particular test to return a result is a relevant issue. Diagnostic tools that are faster but less accurate may be substituted. For example, a patient with a suspected pulmonary embolus and a positive d-dimer blood test in the emergency room (fast but not 100% accurate) may be started on heparin while awaiting a more definitive spiral CT of the chest or angiogram. This provides the soonest effective therapy.

A peculiarity in urologic laboratory testing is found in the analysis of dipstick versus microscopic versus microbiological (culture) urine analysis. Culture results, particularly, will not be available for 48 - 72 h. It is imperative, however, to have collected a sample before starting empiric antibiotic treatment. The safest plan is to consider a complete urinalysis to consist not only of a dipstick test but also microscopic analysis and, if there are any nitrates or white blood cells present, an automatic Gram-positive and Gram-negative microbi-ologic culture.

Dipstick tests are quick but give both false-positive and false-negative results in the presence of some phys-icochemical urine properties as well as certain drugs. Blood detection might be hindered by captopril or vitamin C intake and leukocyte esterase by elevated specific gravity, glycosuria, proteinuria, and oxidating drugs, including some cephalosporins, tetracycline, and gen-tamicin (Simerville et al. 2005).

The sensitivity of dipstick urinalysis ranges from 91 % to 96% for microscopic hematuria, 72% to 97% for abnormal leukocyte esterase, and 19% to 48% for nitrites;

specificity ranges from 65 % to 99 %, 41 % to 86 %, and 92 % to 100%, respectively(Simerville et al. 2005). Under the pressure of cost containment, numerous studies have addressed the diagnostic value of dipstick testing in the emergency room. Two prospective observational studies concluded that, in women with suspected UTI, over- and undertreatment rates were similar for various test cut-off values for urine dipstick and microscopic urine analysis (Lammers et al. 2001) and that microscopy prompted changes in only 6 % of patients with suspected UTI and in none with suspected microhematuria (Jou and Powers 1998). On the other hand, Leman (2002) calculated that microscopy improved the specificity for UTI in women presenting to the emergency room. More importantly, the study revealed the dipstick urinalysis to be susceptible to systemic bias for UTI, resulting in different sensitivity and specificity values in patients with different clinical manifestations (Lachs et al. 1992; Grosse et al. 2005). In short, although the value of microscopy maybe controversial in the general emergency room setting, it is not so in the urologic emergency room. In this specific population, many with severe or recurrent UTI, the practice of obtaining microscopy in addition to dipstick urinalysis is warranted.

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