Lab case 333 interpretation

Question 1:

PH = 7.501, that is mild alkalaemia

HCO3 = 32 mmol/L. So we have metabolic alkalosis.

Next we calculate compensation, for that we use the following formula:

Expected pCO2= 0.7 x HCO3 +  20. According to that the expected CO2 for this patient should be 42.4. this is very close to the CO2 we have (41). Accordingly, this patient has fully compensated metabolic acidosis ((no additional respiratory or metabolic process).

Other abnormal findings:

Hb = 98 g/L. that is low, ( This patient recently underwent major surgery).

Na = 133 mmol/L that is low. However, this patient has blood glucose level of 17 mmol/L. We know that in the presence of hyperglycemia we get pseudo-hyponatraemia.

The equation that we use to correct the Na level is:

Corrected Na = Measure Na + (Glucose -5)/3 = 137 mmol/L. Accordingly, this patient has normal corrected Na level.

K = 2.9 mmol/L. That is moderate hypokalaemia. However, K level is affected by PH. Serum K level usually drops by  0.5 mmol/L for every 0.1 increase in pH above normal. Accordingly, corrected K level will be around 3.2 mmol/L (mild hypokalaemia).

That patient was diabetic, that is why the glucose level was 17 (high)

The final conclusion is: Mild metabolic alkalosis with mild hypokalaemia.


Question 2: 

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

  • C – contraction (dehydration) – Possible
  •  L – liquorice (diuretic), laxative abuse – excluded by taking history
  •  E – endocrine (Conn’s, Cushing’s) – unlikely with low-normal Na level.
  •  V – vomiting, GI loss (villous adenoma) – excluded by taking history
  •  E – excess alkali (antacids) – excluded by taking history
  •  R – renal (Bartter’s), severe K depletion – unlikely, normal bloods previously
  •  P – post hypercapnia – No
  •  D – diuretics  – excluded by taking history.

The most probable cause is dehydration. These results were normalised after 1 bag of normal saline.