Endocrine System Disorders Q 26

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A male client with a tentative diagnosis of hyperosmolar hyperglycemic nonketotic syndrome (HHNS) has a history of type 2 diabetes that is being controlled with an oral diabetic agent, tolazamide (Tolinase). Which of the following is the most important laboratory test for confirming this disorder?

  

    A. Serum potassium level

    B. Serum sodium level

    C. Arterial blood gas (ABG) values

    D. Serum osmolarity

    

    

Correct Answer: D. Serum osmolarity

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Serum osmolarity is the most important test for confirming HHNS; it’s also used to guide treatment strategies and determine evaluation criteria. A client with HHNS typically has a serum osmolarity of more than 350 mOsm/L. The serum osmolality is determined by the formula 2Na + Glucose /18 + BUN / 2.8. The resultant hyperglycemia increases the serum osmolarity to a significant degree. The glucose level in HHS is usually above 600 mg/dL. Hyperglycemia also creates an increase in the osmotic gradient with free water drawn out from the extravascular space from the increased osmotic gradient.

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Option A: Serum potassium, serum sodium, and ABG values are also measured, but they aren’t as important as serum osmolarity for confirming a diagnosis of HHNS. In HHS however, because insulin is still being produced by the beta cells in the pancreas, the generation of ketone bodies is minimal. Insulin inhibits ketogenesis. That aside, in HHS there is a higher level of insulin with an associated lower level of glucagon. Therefore, ketonemia and acidemia are very mild in HHS.

Option B: A client with HHNS typically has hypernatremia and osmotic diuresis. The effect of the increased serum osmolarity on the brain can be very profound. To preserve the intracellular volume, the brain produces idiogenic osmoles. Idiogenic osmoles are substances that are osmotically active. The net effect of the production of these substances is to prevent fluid from moving from the intracellular space into extracellular space and maintain a balanced equilibrium.

Option C: ABG values reveal acidosis, and the potassium level is variable. Beta oxidation of fatty acids produces ketone bodies: acetone, acetoacetate, and beta oxobutyric acid. Accumulation of these substrates produces ketonemia and acidemia. Acidemia from ketone bodies stimulates the kidney to retain bicarbonate ions to neutralize the hydrogen ions. This accounts for the low serum bicarbonate level in DKA.

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