Lab case 438 Interpretation

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Answers:

PH = 7.39, that is within normal range/

pCO2 = 48 mmHg, that is slightly elevated (Can be considered normal for venous blood)

HCO3 = 29 mmol/L. That is high (Normal value is 24 mmol/L), SO, we have metabolic alkalosis.

Next, we will calculate the compensation for metabolic alkalosis. The formula used for that is: Expected CO2 = 0.7 x HCO3 + 20 (+/-5) = 40.3 (Range 35.3 to 45.3)…This patient might have additional mild respiratory acidosis.

It is a good practice to calculate Anion Gap for every patient. AG is calculated as AG=Na – (Cl + HCO3) = 14 for this patient. This patient has addition HAGMA.

So, this patient has Metabolic alkalosis, HAGMA and possible mild respiratory acidosis.

Other abnormal findings:

The most striking abnormal finding for this patient is glucose level of 30 mmol/L. (Severe hyperglycemia).

Na = 137 mmol/L. However, Na level is affected by high sugar level. To calculate the correct Na level we the following equation:

Corrected Na = Measured Na – ( Glucose -5)/3/ For this patient corrected Na level will be: 145 mmol/L… This correction helps us to determine the level of dehydration.

Creatinine level is 190 umol/L. That is high.. We don’t have enough information so far to decide if this level is acute or chronic.

Next, we will look at the possible causes of these results.

For the causes of metabolic alkalosis we use the mnemonic CLEVER PD.

  • C – contraction (dehydration) – Most probable cause.
  •  L – liquorice (diuretic), laxative abuse – excluded by taking history
  •  E – endocrine (Conn’s, Cushing’s) – unlikely with 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, usually gets diagnosed early in life.
  •  P – post hypercapnia – No
  •  D – diuretics  – excluded by taking history.

 

For the causes of HAGMA we use the mnemonic CAT MUDPILES

  • C = cyanide, carbon monoxide – No
  • A = alcoholic ketoacidosis and starvation Ketoacidosis, excluded by taking history.
  • T = toluene, excluded by taking history.
  • M = methanol, metformin, excluded by taking history/
  • U = uraemia.Possible
  • D = diabetic ketoacidosis, unlikely with normal lactate and ketones.
  • P = phenformin, pyroglutamic acid, paraldehyde, propylene glycol, paracetamol. excluded by taking history
  • I = iron, isoniazid. excluded by taking history
  • L = lactate.No, lactate level is normal
  • E = ethanol, ethylene glycol, excluded by taking history
  • S = salicylates. excluded by taking history.

Accordingly, the most possible causes are dehydration and uraemia.

To calculate serum osmolality we need urea level to decide if this has HHS or not. However, in the presence of HAGMA with no other causes other than uraemia can explains it. We decided to treat as HHS.

Urea level came back to be 24 mmol/L

That gave as serum osmolarity of 137 x 2 + 30 + 24 = 328

To calculate serum osmolarity, use the measured Na level. As the drop in serum level of Na during hyperglycemia is caused my movement of water from the intra-cellular compartment to the extracellular compartment.