Lab case 406 interepretation


PH = 7.56, that is moderate alkalaemia

HCO3 = 38.4 mmol/L, so we have metabolic alkalosis.

Next, we will calculate the compensation. For metabolic alkalosis we use the following equation:

Expected pCO2 = 0.7 x HCO3 + 20 (+/- 5) = 46.88 (Acceptable range of 41.8 to 51.8). This patient’s pCO2 is 42 mmHg. It is with in acceptable range. So, we can say that this patient has pure metabolic alkalosis.

It is always a good practice to calculate the anion gap. Anion gap is calculated as:

AG = Na – (Cl + HCO3) = 9.6. So there is no additional HAGMA.

Other abnormal findings:

K = 2.5 mmol/L that is moderate hypokalaemia.

Cl = 86 mmol/L that is hypochloraemia.

Lactate = 3 mmol/L, that is mildly elevated and can be a marker for reduced tissue perfusion / dehydration.

Next, need to look at the causes keeping in our mind that the patient is post-ictal and which of the causes of metabolic alkalosis can cause seizures.

For the deferential diagnosis of metabolic alkalosis we use the mnemonic CLEVER PD

  • C – contraction (dehydration) – Possible
  •  L – liquorice (diuretic), laxative abuse – Some alcoholic drinks (Ouzo, Raki has chemical similar to liquorice) ***
  •  E – endocrine (Conn’s, Cushing’s) – unlikely with low-normal Na level.
  •  V – vomiting, GI loss (villous adenoma) – Possible, especially with the presence of hypokalaemia and hypochloremia (Upper GI vomiting).
  •  E – excess alkali (antacids) – Possible
  •  R – renal (Bartter’s), severe K depletion – unlikely, normal bloods previously
  •  P – post hypercapnia – No, it needs longer time to develop, unlikely with post-ictal hypercarbia.
  •  D – diuretics  – possible.

*** Stewart et al. have proposed that licorice acts by inhibiting Cortisol oxidase, a component of the widely distributed 11β-hydroxysteroid dehydrogenase system that converts Cortisol to cortisone, producing a state of apparent mineralocorticoid excess similar to that in children with 11/3-hydroxysteroid dehydrogenase deficiency.

 This patient was alcoholic, he developed vomiting due to gastritis and kept on vomiting every-time he had alcohol. Ended with alcohol withdrawal seizure.

The Low Potassium and Chloride were due to vomiting.


*** Licorice-Induced Hypermineralocorticoidism. The New England Journal of Medicine.

Robert V. Farese, Jr., M.D., Edward G. Biglieri, M.D., Cedric H.L. Shackleton, Ph.D., Ilan Iron y, M.D.and Rosita Gomez-Fontes, M.D.



Special thanks to Dr Mostafa Mohamed Said Abdalla Mohamed Othman for providing the details of this case.