Table 1.
Suspected causes of negative anion gap run on automated clinical chemistry analyzers.
| Likely reason for negative anion gap1 | Number of unique patients with one or more specimens in the category2 | Number of samples2 |
|---|---|---|
| Spurious event (e.g., laboratory error, contaminated specimen) | 63 | 63 |
| Chronic respiratory acidosis with compensatory metabolic alkalosis | 36 | 47 |
| Hypoalbuminemia | 29 | 38 |
| Hypercalcemia | 0 | 0 |
| Hypermagnesemia | 0 | 0 |
| Polymyxin B | 0 | 0 |
| Polyclonal gammopathy | 0 | 0 |
| Monoclonal proteins | 6 | 6 |
| Marked hyperkalemia | 1 | 6 |
| Lithium toxicity | 0 | 0 |
| Pseudohyponatremia – hypertriglyceridemia | 0 | 0 |
| Pseudohyponatremia – marked hypercholesterolemia | 0 | 0 |
| Pseudohyponatremia – hyperproteinemia | 0 | 0 |
| Pseudohyperbicarbonemia – ketoacidosis | 0 | 0 |
| Bromism | 0 | 0 |
| Iodine | 0 | 0 |
| Thiosulfate | 0 | 0 |
| Salicylate poisoning | 0 | 0 |
1
Items in this column are those recognized in the published literature as associated with negative anion gaps.
2
Attribution of cause determined by detailed chart review of laboratory studies and clinical documentation. Spurious events were those with at least two of the following: (a) no other explanation likely given clinical history, (b) result inconsistent with baseline and/or follow-up laboratory studies, (c) clinical documentation attributing the result to “laboratory error” or similar language, or (d) cluster of similar suspicious results on same day.