Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (795 page)

   Plasma levels drop quickly within 5 minutes if RBCs are not separated from plasma once collected.

   Amphetamines and amphetamine-like compounds, appetite suppressants, bromocriptine, buspirone, caffeine, carbidopa–levodopa, clonidine, dexamethasone, diuretics (in doses sufficient to deplete sodium), ethanol, isoproterenol, labetalol, methyldopa, MAO inhibitors, nicotine, nose drops, propafenone (Rythmol), reserpine, theophylline, tricyclic antidepressants, and vasodilators may interfere with this test, and the results may not be predictable.

   Children under 2 years of age show elevated response to stress.

   For accurate results, patient should be in supine for 30 minutes prior to collection.

CELL COUNT, BODY FLUID ANALYSIS
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   Introduction

   This section focuses on the microscopic evaluation of fluids accumulated in body cavities: cerebrospinal, pleural, pericardial, and peritoneal (ascites). Synovial fluids are described below under “Other Body Fluids.” Aspiration followed by chemical, microscopic, cytologic, microbiologic, and, if indicated, flow cytometry examinations should help determine the etiology of accumulated pathologic fluids by providing important information regarding infection, hemorrhage, inflammation, or malignant infiltration. Total cell counts are performed using undiluted (or in the case of very high counts, diluted) body fluids with a hemocytometer. Differential counts are done using a smear following centrifugation (Cytospin) and staining with Wright-Giemsa stain. Bacterial identification and cultures and the chemistry of body fluids are described separately.

CEREBROSPINAL FLUID (CSF)
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   Definition

   CSF is produced by the choroid plexus in the lateral third and fourth ventricles of the brain. In normal adults, the total CSF volume is 90–150 mL. Eighty percent of the CSF is contained in the arachnoid space in the cranium and spinal cord, where a small amount can be extracted for examination, most commonly through a lumbar puncture. CSF pressure is measured by a manometer.

   
Normal values:

   Appearance: clear, colorless

   Normal opening adult pressure: 90–180 mL of water in an adult in the lateral decubitus position with the legs and neck in a neutral position

   Cell count and differential (Table 16.17):