Lab case 325 interpretation

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Question 1:

PH = 7.028, that is severe acidaemia.

HCO3 = 6 mmol/L. So, we have metabolic acidosis.

Next we need to calculate the anion gap and compensation.

AG = Na – (Cl + HCO3) = 135 – (118 + 6) = 11, this is with in normal range it means we have NAGMA.

However, if we include K (In this the expected AG should be 16 or less), AG will be 17, In this case it will be HAGMA… To confirm what type of metabolic acidosis we have here we can calculate Delta ratio. This is  AG – 12 (or 16)/ 24 – HCO3.

Delta ratio for AG of 17 = 1/18 = 0.05, So we have NAGMA here.

To calculate compensation we use winter’s formula, that is:

Expected PCO2 = 1.5 x HCO3 + 8  (+/- 2). = 15 – 19. PCO2 here is 24. Se we have additional respiratory acidosis.

So we have NAGMA with respiratory acidosis.

Other abnormal findings:

K = 6.3 mmol/L. That is moderate hyperkalaemia. K+ increases 0.6 mmol/L for each 0.1 PH units decrease below 7.4. Accordingly, corrected K should be:

6.3 – (7.4 – 7.028) x 0.6/ 0.1 = 4.1 mmol/L.

Cl = 118 mmol/L, that is htperchloraemia

Hb = 88, So, this patient has moderate anaemia.

Creatinine = 243 nmol/L, this is high. For a 67 year old man, this level means this patient has GFR of 23. This patient has stage 4 kidney disease….This patient had urea level of 55 mmol/L

Final conclusion.. This patient has Hypercloraemic normal anion gap metabolic acidosis with respiratory acidosis and stage 4 kidney disease+ anaemia.

Next we need to look at the causes of NAGMA.

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, Possible. Has to be dietary as no treatment or IV fluids were given at the time when this VBG test was performed.
  • Diarrhoea, No diarrhoea in the history
  • Carbonic anhydrase inhibitors. Patient denied taking this type of medication.
  • Renal tubular acidosis, Possible.
  • Addison’s disease… Unlikely, as it is usually associated with hypochloraemia.
  • Pancreatoenterostomies. Unlikely, as the patient had no previous surgical history.

According to that the most probable cause is RTA due to renal impairment.

 Question 2

  1. Drugs
    • Acetazolamide, steroids, oestrogens, androgens
    • Thiazides, Carbonic anhydrase inhibitors.
    • IV NaCl replacement or hypertonic saline
  2. Metabolic
    • NAGMA
    • Respiratory alkalosis (Decreased Ca, K, Mg, increased Cl)
  3. Endocrine
    • Hypothalamic lesion (Increased Na) (Decreased thirst perception)
    • Adrenocortical hyperfunction
  4. Renal
    • RTA
    • Acute renal failure
    • Diabetic insipidus
  5. GIT
    • Dehydration
    • prolonged diarrhoea
  6. Fictitious
    • Bromides toxicity (Bromide in serum will not be distinguished from chloride in routine testing, so intoxication may show spuriously increased chloride)