Lab case 409 interpretation

Question 1:

PH = 7.17, that is moderate acidaemia.

HCO3 = 14 (less than 24). So, we have metabolic acidosis.

Because we have metabolic acidosis, then we need to calculate the compensation and anion gap.

We calculate compensation using winter’s formula, that is

Expected PCO2 = 1.5 x HCO3 + 8 (+/- 2). In this case the expected PCO2 should be (1.5 x 14 +8   +/- 2) = 27 – 31. PCO2 is 30, it fits within the expected range. Accordingly, we don’t have additional respiratory process in this case (fully compensated).

Anion gap = {Na – (Cl + HCO3)} = 11 in this case. So we have normal anion gap (less than 12).

So, this patient has pure normal anion gap metabolic acidosis (NAGMA).

Other findings:

Na = 123 mmol/L, that is moderate hyponatraemia. K, with in normal range.

BSL = 3.4 mmol/L. This level is considered normal in non-diabetic patient, however is it is at low-normal side of the scale.

Lactate = 3.4 mmol/L. That is moderate hyperlactataemia, sign of reduced tissue perfusion.

The final conclusion is NAGMA with moderate hyponatraemia.

We use the mnemonic USEDCARP  for the differential diagnosis/causes of NAGMA

  • Ureteroenterostomies. Unlikely, as the patient had no previous surgical history.
  • Small bowel fistula, Unlikely as the patient had no previous surgical history
  • Excess Chloride, Unlikely, Cl level = 98 mmol/L
  • Diarrhoea, No diarrhoea in the history
  • Carbonic anhydrase inhibitors. Patient denied taking this type of medication.
  • Renal tubular acidosis, Usually not associated with hyponatraemia.
  • Addison’s disease… Possible.
  • Pancreatoenterostomies. Unlikely, as the patient had no previous surgical history.

From the list above, Addison’s disease is the only possible diagnosis.

Addison’s disease usually present with NAGMA, with hyperkalaemia and hyponatraemia. This happens due to inadequate production of the steroid hormones cortisol and aldosterone from the adrenal cortex. Hypoglycemia can be a feature due to cortisol deficiency. High lactate is due to dehydration that is secondary to aldosterone deficiency.

This patient had normal Potassium level as she was using Salbutamol for her asthma. There are reported cases in the literature of asthma secondary to Addison’s disease, again due to cortisol deficiency.

 Question 2: 

Management involves 3 aspects

  1. Correct dehydration, IV hydration, usually with normal saline
  2. correct electrolytes abnormalities. ( Correct hyperkalaemia – not in this case).
  3. Intravenous hydrocortisone, 100 mg, QID. (We don’t usually use fludrocortison/ aldosterone replacement in the emergency departments as hydrocortisone in high doses has mineralocorticoid effect).