Query EDTA contamination

HOSP # MRN96038757 WARD F17 Surgical ward
CONSULTANT   Dr. Jody Rusch DOB/AGE 26 y male

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

Date 16/03/2020 14/03/2020 13/03/2020 12/03/2020 12/03/2020 11/03/2020 10/03/2020 08/03/2020
Time 07:22 10:38 10:30 19:59 12:32 21:23 16:05 12:53
Na 144   141     141          δ-  138     143   δ+  145     140  
K >10 2.6   3.0 L   3.0 L INVH   3,2 L δ+  3,7     3.0 L
Cl                                                        
Urea 4.4   5,1     5.0            5,5     6,9   δ+  5,5     2,5  
Creat 47    60 L    60 L           64      67      66      62 L
Ca 1.63  2,24    2,27           2,13 L  2,23    2.30    2,23  
Mg 0.38 δ- 0.67   δ+ 0.90           0.77    0.82    0.75    0.74  
Phos 1.1  1.50 H  1,31           1,28    1,38    1,23    1,17  
Uric acid                                                        
Total prot CEGK                      CEGK                     
Alb 30                         39                    40  
Total bili <3                          3 L                   4 L
Conj bili 2                      INVH                   2  
ALT 35                         28                    32  
AST 33                      INVH                  28  
ALP 118                        137 H                 158 H
GGT 99                         96 H                 113 H
LD 138                      δ+  465 H                 317 H
CRP 2                          7                     6  
Table 1 – Results in bold indicative of likely EDTA contamination.

Other Investigations

Repeated results later in the afternoon:

Date 16/03/2020 16/03/2020
Time 13:04 07:22
Na 144 144
K δ+  3,3 L >10
Cl              
Urea 4.6 4.4
Creat 55 47
Ca 2.2 1.63
Mg 0.56 0.38
Phos 1.06 1.1
Uric acid              
Total prot CEGK CEGK
Alb 37 30
Total bili     3 L <3
Conj bili 2 2
ALT 46 35
AST 40 33
ALP 151 118
GGT 121 99
LD 230 138
CRP 2 2
Initial results on the right. Repeated (new) results on the left.

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.