Abnormal Result

Potassium more than 10 mmol/L on the ion-selective electrode.

Presenting Complaint

The patient was admitted in surgery after bowel surgery, on total parenteral nutrition.

History

Surgery was done due to bowel obstruction.

Examination

Not available.

Typically:

A hallmark of small bowel obstruction is dehydration, which manifests as tachycardia, orthostatic hypotension, and reduced urine output, and, if severe, dry mucus membranes.

●Abdominal inspection will identify a variable degree of abdominal distention.

●Abdominal auscultation – Acute mechanical bowel obstruction is characterized by high-pitched “tinkling” sounds associated with the pain. With significant bowel distention, bowel sounds may become muffled, and as the bowel progressively distends, bowel sounds can become hypoactive.

●Abdominal percussion – Distention of the bowel results in hyperresonance or tympany to percussion throughout the abdomen. However, fluid-filled loops will result in dullness. If percussion over the liver is tympanitic rather than dull, it may be indicative of free intra-abdominal air. Tenderness to light percussion suggests peritonitis.

●Abdominal palpation may identify any abdominal wall or groin hernias, or abnormal masses.

Laboratory Investigations

Other Investigations

Repeated results later in the afternoon:

Final Diagnosis

Likely EDTA contamination causing a falsely elevated potassium, decreased Calcium, Magnesium and ALP. The clinician was contacted and it was indeed medical undergraduate students who had taken the bloods, probably not realizing the order of draw, or toppling up the serum blood with some of the blood taken in an EDTA tube. This is evidenced by the high potassium, low calcium, magnesium and ALP. It is however evident that most other analytes were also lower than the repeat bloods later that day, hence:

Another likely possibility of the results in question could have been drip line contamination due to a potassium-containing fluid. The patient was indeed on total par-enteral nutrition, which usually contain large doses of potassium. This could be explained by the dilution of most analytes (as opposed to the raised potassium and normal sodium).

Take Home Message

It does not require much potassium EDTA contamination to evoke spuriously abnormal results. Potassium EDTA works as an anticoagulant by inhibiting clotting by chelation of the divalent cations such as calcium and magnesium, essential for the divalent cation-dependent proteolytic enzymes involved in the clotting cascade.

Gross potassium EDTA contamination of blood samples can be recognized by unexpected marked pseudohyperkalaemia and pseudohypocalcaemia. Serum alkaline phosphatase (ALP) activity can also be reduced in the presence of potassium EDTA contamination. Additionally, aspartate transaminase, alanine transaminase, lactate dehydrogenase, creatine kinase, amylase, unsaturated iron-binding capacity and bicarbonate can all be detrimentally affected in the presence of potassium EDTA contamination. Notably, some papers report potassium EDTA contaminated samples were mainly from inpatients compared to outpatients and primary care and the authors speculated that this is because blood samples in outpatients and general practice are largely but not exclusively collected by trained phlebotomists. It is our job as laboratorians to educate the newly trained clinicians about order of draw.

It is unfortunate that I couldn’t locate the undergraduate student who had taken these bloods, but at least the attending clinician was made aware of EDTA contamination.

HOSP #		WARD	False Bay Hospital Casualties
CONSULTANT		DOB/AGE	33y Female

Abnormal Result

Urea 0.8 mmol/L; Creatinine 10 umol/L; Sodium 154 mmol/L; Potassium 5.4 mmol/L

Presenting Complaint

Above results do not make sense for a 33 year old female, except if muscle weight is extremely low.

History

Examination

N/A

Laboratory Investigations

Inspection of the sample:

Other Investigations

Lactate on analyser as done on serum sample: >22 mmol/L, dilution made: 1 in 10 revealed a lactate of 26.8 mmol/L in the sample. This could explain that Ringers Lactate was the contaminant in the sample, but can only be hypothesized with the available evidence.

Hematology results:

Final Diagnosis

Take Home Messages

Lactate cannot be measured in SST (serum separator tubes) without taking into account the fact that the red cells will continue to metabolize the glucose in the sample to lactate via anaerobic metabolism through glycolysis.

Lactate concentration increases linearly over time, in whole blood. Factors affecting the rate of production are, among others:

• Temperature
• Glucose concentration
• Additives in the blood tubes such as NaF

NaF inhibits enolase, an enzyme acting late in the glycolytic pathway, and has no effect on enzymes that act early in the glycolytic pathway. … Glycolysis is instantly inhibited in erythrocytes, leukocytes and platelets when the blood pH is maintained between 5.3 and 5.9 with a citrate buffer.

Sage Journals: Ann Clin Biochem 2013;50: 3–5. DOI: 10.1258/acb.2012.012135