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)
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.
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
Compartment shift
Metabolism by live cells
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.