The 'gap' in the 'plasma osmolar gap'

Accuracy of a Glycerol Dehydrogenase Assay for Ethylene Glycol Detection

INTRODUCTION

Ethylene glycol (EG) is a frequently considered toxicant in poisoned patients. Definitive diagnosis relies on gas chromatography (GC), but this is unavailable at most hospitals. A glycerol dehydrogenase (GDH)-based assay rapidly detects EG. A rapid turnaround time and wide availability of necessary instrumentation suggest this method could facilitate the rapid detection of EG.

METHODS

This is a prospective, observational analysis of banked, remnant serum samples submitted to the laboratory of a large, multi-hospital healthcare system. Samples were submitted over a 12-month period for the explicit purpose of testing for suspected EG ingestion. All samples underwent GC and the GDH-based assay.

RESULTS

Of the 118 analyzed samples, 88 had no EG detected by GC, and 30 were "positive." At the manufacturer's threshold of 6 mg/dL EG, there was 100% (95%CI; 88.7-100) positive percent agreement (PPA) and 98% (92.1-99.6) negative percent agreement (NPA). Adjusted to a threshold of 9 mg/dL, both the PPA and NPA were 100%. Deming regression of the observed concentrations revealed a slope of 1.16 (1.01 to 1.32) and intercept of -5.3 (-8.9 to -1.7).

CONCLUSIONS

The GDH assay provides a sensitive and specific method for the detection and quantification of EG that is comparable to a GC-based method. More widespread use of this rapid, inexpensive assay could improve the care of patients with suspected toxic alcohol exposure. Further study is needed to evaluate the test performance in real-time patient treatment decisions.

From Toxic Ingestion to Cancer: Dramatic Acidosis as a Myeloma-Defining Event

Acute kidney failure has myriad causes and presentations. This is a case of an individual with a history of alcohol abuse and a previous suicide attempt presenting with acute kidney failure and altered mentation accompanied by an anion gap metabolic acidosis with an elevated osmolar gap. These findings were concerning for toxic alcohol ingestion, but the patient was ultimately diagnosed with multiple myeloma. This case demonstrates the multiple factors that can impact both the anion and osmolar gaps. It shows that the traditionally held dogma about the meaning of anion or osmolar gaps may cloud an otherwise more obscure etiology. It illustrates a dramatic presentation of acute myeloma, for which early recognition is essential to initiate appropriate chemotherapy for a chance at preservation of renal function.

Ethylene Glycol Toxicity in the Setting of Recurrent Ingestion: A Case Report and Literature Review

Ethylene glycol (EG) poisoning is a toxicologic emergency requiring high clinical suspicion and early diagnosis to prevent life-threatening complications. Direct EG quantification methods involve cumbersome and time-consuming laboratory tests of limited utility in the emergency setting. Accordingly, the osmolal gap is frequently employed as a surrogate screening method in cases of suspected toxic alcohol poisoning. However, the osmolal gap has several inherent limitations to be considered when used as a diagnostic tool for EG toxicity. Although many of these limitations are widely acknowledged, the clinical finding of a normal serum osmolal gap in the setting of recurrent toxic alcohol exposure is an observation that has remained largely unexplored. The purpose of this case report is to characterize the accelerated osmolal gap to anion gap conversion that may occur in the setting of chronic toxic alcohol abuse.