Saturday, April 14, 2012

The Clinical Approach to the Acutely Ill Patient- Laboratory Testing


The Clinical Approach to the Acutely Ill Patient


Diagnosis
The Use of Guidelines and Algorithms
The Emergency Setting
 History
Physical Examination
Primary Survey
Secondary Survey
Laboratory Testing
Imaging
Sonography
Plain Abdominal Films
Intravenous Pyelography
Computed Tomography
Magnetic Resonance Imaging
Chest X-Ray 


Laboratory Testing
In all cases, laboratory values that appear erroneous or do not make sense should be quickly rechecked before irrevocable لا رجعة فيه steps are taken in the patients 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 4872 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 microbiologic culture. Dipstick tests are quick but give both false-positive and false-negative results in the presence of some physicochemical 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 gentamicin
.
The sensitivity of dipstick urinalysis ranges from91% 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.

Many with severe or recurrent UTI, the practice of obtaining microscopy in addition to dipstick urinalysis is warranted.


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