Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1305 page)

   
Complete or partial nephrogenic DI or psychogenic polydipsia:
Increased ADH levels. Giving ADH does not increase urine osmolality in complete nephrogenic DI.

   
Complete or partial neurogenic DI:
Low ADH relative to plasma osmolality. Giving ADH increases urine osmolality approximately 200 mmol/kg but not in partial nephrogenic DI.

   Limitations

   Some nonosmotic stimuli, such as smoking, hypotension, and nausea, can increase ADH release. If a transient episode of hypotension and nausea occurs, the entire test is invalid and it needs to be repeated in another day.

   Complete emptying of the bladder during each collection is important because incomplete emptying may dilute the urine of the next collection.

   The plasma sample for osmolality measurement should be from heparinized blood, and EDTA should be avoided because it artificially increases the osmolality by 3–10%.

   The plasma for ADH measurement should be collected without disturbing the buffy coat in order to minimize the contamination from platelets.

   The test should be performed only when the patient’s basal plasma sodium concentration is within the normal range, otherwise it may cause potential harm to the patient.

   The test should not be performed in patients with renal insufficiency, uncontrolled DM, or hypovolemia of any cause or uncorrected adrenal or thyroid hormone deficiency.

   Patients should be observed for the entire duration of the test.

   For pregnant patients, the blood sample for ADH measurement should be drawn into a tube that contains 6 mg of 1,10-phenanthroline to prevent the degradation of ADH by placental vasopressinase. The results should be evaluated in the context of altered relationship between the plasma osmolality/sodium concentration and the plasma ADH concentration.

WHITE BLOOD CELL: INCLUSIONS AND MORPHOLOGIC ABNORMALITIES
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   Definition