Lab case 391 interpretation


PH = 7.579, that is severe alkalaemia

HCO3 = 45 mmol/L. So, we have metabolic alkalosis. Next, we need to calculate the expectation. For metabolic alkalosis we use the following formula:

Expected pCO2 = 0.7 x HCO3 + 20 (+/-5).

Accordingly, expected pCO2 for this patient is = 0.7 x 45 + 20 = 51.5 (46.6 – 56.5). This patient’s pCO2 is 48 mmol/L. (within the expected range). That means there is no associated respiratory process.

Other abnormal findings:

Cl = 82 mmol/L, that is moderate hypochloremia.

Hb = 200 g/L, that is high haemoglobin level.

The most concerning abnormality in these blood gases is the significantly high lactate level of 6.9 mmol/L. (Lactate level higher than 5 mmol/L is almost always associated with HAGMA).

It is a good practice to calculate the anion gap in every blood gases results. For this patient, the anion gap is:

143 – (45 + 82) = 16, So we have additional HAGMA.

Next, we will look at the potential causes:

For the differential diagnosis of metabolic alkalosis, we use the mnemonic CLEVER PD.

  • C – contraction (dehydration)
  •  L – liquorice (diuretic), laxative abuse
  •  E – endocrine (Conn’s, Cushing’s)
  •  V – vomiting, GI loss (villous adenoma)
  •  E – excess alkali (antacids)
  •  R – renal (Bartter’s), severe K depletion
  •  P – post hypercapnia
  •  D – diuretics

From the list above vomiting is the most probable explanation.

For the associated HAGMA, most probably it is due to the significantly high lactate level.

We don’t have enough information to tell what the cause is for the elevated lactate level.