Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1144 page)

   Cushing syndrome

Decreased In

   Acute renal failure

   Malabsorption

   Chronic potassium deficiency states

   Addison disease

   Severe GN

   Pyelonephritis

   Nephrosclerosis

   Limitations

   Urinary potassium may be elevated with dietary (food and/or medicinal) increase, hyperaldosteronism, renal tubular acidosis, onset of alkalosis, and with other disorders.

   Urine chloride is often ordered with sodium and potassium as timed urine. The urinary anion gap [Na
⁺
− (Cl
⁻
+ HCO
₃
⁻
]) or [(Na
⁺
+ K
⁺
) − (Cl
⁻
)] is useful in the initial evaluation of hyperchloremic metabolic acidosis.

PREALBUMIN

   Definition

   This 54-kDa protein tetramer is synthesized in the liver, choroid plexus, CNS, placenta, intestine, pancreas, and meninges. It contains two binding sites for thyroid hormones T
₃
and T
₄
and two binding sites for serum retinol-binding protein. These different binding sites do not overlap. As a thyroid hormone transport and binding protein, transthyretin binds 10–15% of serum T
₃
and T
₄
for transport in the blood. In the CSF, where there is typically no albumin or thyroglobulin present, transthyretin serves as the only CSF-binding protein for T
₃
and T
₄
. The presence of high concentrations of transthyretin in the CSF makes it a key indicator of leakage of the CSF into the sinus cavities, eyes, and ears when cranial trauma has occurred. Prealbumin is a negative acute-phase reactant. Other names: prealbumin (PA), thyroxine-binding prealbumin (TBPA).