List 2 causes for the following combination  of findings observed on a serum sample.

Test

Value

Normal Range

Measured osmolality*

310 mOsm/L

(280 – 290)

Sodium*

125 mmol/L

(135 – 145)

Potassium

4 mmol/L

(3.5 – 5.0)

Chloride

98 mmol/L

(95 – 105)

Bicarbonate*

21 mmol/L

(22 – 32)

Glucose

6 mmol/L

(4 – 6)

Urea

8 mmol/L

(6 – 8)

 

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College Answer

•    Raised osmolar gap with normal AG
•     Mannitol
•     Glycine
•     Ethanol

Discussion

These biochemistry results are provided without any history.

Let us dissect them systematically.

  1. The A-a gradient cannot be calculated
  2. The pH is not supplied
  3. The PaCO2 is not reported
  4. The SBE is not offered, but the bicarbonate is 21, suggesting a trend towards metabolic acidosis.
  5. The respiratory compensation cannot be assessed.
  6. The anion gap is normal:
     (125) - (98  + 21) = 6, or 10 when calculated with potassium
  7. The osmolar gap is raised: 310 - (2 × 125 + 6 + 8) = 46

So, this is a hyperosmolar state without metabolic acidosis. It stands to reason that the extra osmoles are probably not participating in any sort of metabolism.

This sort of picture is consistent with the following scenarios:

  • Mannitol therapy
  • Glycine (post-TURP syndrome)
  • Alcohol intoxication (early in the night)

Glucose and urea may contribute in other scenarios, but in this set of biochemistry results they are represented by normal values.

The possible contributors to the hyperosmolarity are discussed briefly in the chapter on hyperosmolar hypernatremia.

 

References

References

Yun JJ, Cheong I. Mannitol-induced hyperosmolal hyponatraemia. Intern Med J. 2008 Jan;38(1):73.

Rothenberg, David M., Arnold S. Berns, and Anthony D. Ivankovich. "Isotonic hyponatremia following transurethral prostate resection." Journal of clinical anesthesia 2.1 (1990): 48-53.

 

Liamis, George L., et al. "Mechanisms of hyponatraemia in alcohol patients."Alcohol and Alcoholism 35.6 (2000): 612-616.

Taivainen, Hanna, et al. "Role of plasma vasopressin in changes of water balance accompanying acute alcohol intoxication." Alcoholism: Clinical and Experimental Research 19.3 (1995): 759-762.