The following data were obtained from a patient who had been observed overnight in the Emergency Department with minor fractures. The patient is otherwise well and currently asymptomatic.

Venous Biochemistry

Parameter

Patient Value

Normal Adult Range

Sodium

131 mmol/L*

135 – 145

Potassium

>10 mmol/L*

3.5 – 4.5

Chloride

98 mmol/L

95

105

Bicarbonate

14 mmol/L*

22

26

Glucose

1.2 mmol/L*

3.5-6.1

Creatinine

70 μmol/L

70

120

Lactate dehydrogenase (LDH)

600 U/L*

60

100

Phosphate

2.10 mmol/L*

0.65

– 1.45

Lactate

4.3 mmol/L*

< 2.0

Give the most likely cause for the above biochemical abnormalities?

Justify your answer.    (40% marks)

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College Answer

Artefact; – This blood sample was left longer than 6 hours before it was processed for above investigations. (Note to examiners - This is not just a haemolysed sample – haemolysis alone does not cause hypoglycaemia and lactic acidosis, though it will cause other abnormalities).

1)    Potassium, phosphate and LD enter the serum from red cell due to haemolysis and Na/K pump dysfunction.

2)    Low Na – shift into red cell in exchange for potassium.

3)    RBCs consume glucose and generate lactate.

Discussion

An ideal reference for this answer is a 2008 paper by Tanner et al, examining the delayed processing of samples collected in rural and remote areas. The studies have discovered that over 24 hours of stoarge various changes take place. These changes (and the reasons behind them) were as follows:

Escape of cellular contents due to haemolysis

  • Potassium increases. After 24 hours, Tanner et al found the original K+ level of 3.8 increased to 8.0.
  • Phosphate increases. In the same study, the PO4- went from an average value of 1.36 to 4.36.
  • Total protein increases
  • LDH increases

Compartment shift

  • Sodium decreases

Metabolism by live cells

  • Acidosis develops
  • LDH increases (also because of anaerobic metabolism)
  • Glucose decreases (consumed by RBCs)
  • Lactate increases (produced by RBCs)
  • PaO2 decreases and PaCO2 increases as a consequence of RBC metabolism (in the experiments by Biswas et al (1982), the PaO2 fell by up to 40% in samples which were stored at room temperature for twenty minutes. This ameliorated by storing the sample at 4°C, but all sorts of other problems develop as a consequence of this).

References

References

Baird, Geoffrey. "Preanalytical considerations in blood gas analysis." Biochemia medica 23.1 (2013): 19-27.

Biswas, C. K., et al. "Blood gas analysis: effect of air bubbles in syringe and delay in estimation." Br Med J (Clin Res Ed) 284.6320 (1982): 923-927.

Woolley, Andrew, and Keith Hickling. "Errors in measuring blood gases in the intensive care unit: effect of delay in estimation." Journal of critical care 18.1 (2003): 31-37.

Hankinson, S. E., et al. "Effect of transport conditions on the stability of biochemical markers in blood." Clinical Chemistry 35.12 (1989): 2313-2316.

Tanner, Melissa, et al. "Stability of common biochemical analytes in serum gel tubes subjected to various storage temperatures and times pre-centrifugation." Annals of Clinical Biochemistry 45.4 (2008): 375-379.