Staten Island Corner: VBG for DKA? - The Original Kings of County

Welcome to this month’s edition of Staten Island Corner. The motivation for this comes from a common question that I am sure all of you have had at one point or another. The other day during a shift there was a debate about the accuracy of ruling in or ruling out DKA based on the shock panel alone. Everybody involved would make their point based on personal cases or the way the bicarbonate is measured, but when one of the attendings said, “What does the data show?”…..there was silence from everyone (including the attendings.) We all realized that nobody had any idea what the literature showed.

So here it goes…. From my search (for whatever that is worth) I found the grand total of ONE article that addresses this exact question. That’s right ONE. The authors of the one article also agree with me because they state in their introduction that they are not aware of any other studies addressing this question.

This prospective observational study was done in Los Angeles at USC. The goal of the study was to assess the accuracy of the VBG in diagnosing DKA and to look at the correlation between VBG and serum chemistry electrolytes in hyperglycemic patients. Patients over the age of 18 with a finger stick over 250 were eligible for the study. Exclusion criteria were critical illness, in police custody, unable to give informed consent, and VBG and serum chemistries collected greater than 30 min of each other. DKA was defined as glucose >= 250, anion gap > 10, bicarbonate < 18, pH <= 7.30, and presence of ketones on UA. 342 patients qualified for the study and 46 of them (13.5%) had DKA. The sensitivity and specificity of VBG for diagnosing DKA were 97.8% (95% CI 88.5% to 99.9%) and 100% (95% CI 98.8% to 100%). The PPV and NPV were 95% (95% CI 92.1% to 100%) and 99.7% (95% CI 98.1% to 100%). The positive and negative likelihood ratios were 582 (95% CI 36.5 to 9290.1) and 0.02 (95% CI 0.003 to 0.15). There was one case of DKA that was missed (bicarbonate of 19 on the VBG and 15 on the serum chemistry). The average difference between VBG and serum chemistry of the following were: Sodium by 2.0, Chloride by 4.0, bicarbonate by 1.6, and anion gap by 4.5.

There were two important limitations to the study that the authors acknowledged. The first being the small sample size and the second being the fact that other institutions may have other laboratory equipment.

The implications of this can potentially be huge in two important areas: total cost and ED throughput. If your only concern with a patient is to rule out DKA and you are able to confidently send one test (in addition to a UA for ketones) as opposed to multiple (we all know that if you are sending a chemistry panel, you will also send a CBC and probably PT/PTT) you will be able to save a significant amount of money on each patient. In addition to money saved, the turnaround time for a shock panel is significantly shorter than a chemistry panel. If we multiple this by the growing numbers of patients with uncontrolled diabetes in the US, we can potentially have a large impact.

I would like to hear what people think about this topic and how comfortable people are with just sending the shock panel.

References:

Menchine M, Probst MA, Agy C, Bach D, Arora S. Diagnostic accuracy of venous blood gas electrolytes for identifying diabetic ketoacidosis in the emergency department. Acad Emerg Med. 2011 Oct;18(10):1105-8. doi: 10.1111/j.1553-2712.2011.01158.x. Epub 2011 Sep 26.

The views expressed on this blog are the author's own and do not reflect the views of their employer. Please read our full disclaimer here. Any references to clinical cases refer to patients treated at a virtual hospital, Janus General Hospital.