Is the effect of hemolysis on plasma ammonia measurement overrated?

Author(s): El-Khoury JM, Bunch DR, Wang S

Publication: Arch Pathol Lab Med, 2012, Vol. 136, Page 471-2

PubMed ID: 22540295 PubMed Review Paper? No

Purpose of Paper

The purpose of this paper was to determine the effects of hemolysis and storage on plasma ammonium levels.

Conclusion of Paper

Ammonium levels in plasma increased with increasing hemolysis. Higher levels of ammonium were measured in specimens when added hemolysate was produced by shearing rather than by the osmotic method with freezing, however, the rate of increase in ammonium levels with increasing hemolysis was greater when the hemolysate was produced by the osmotic method rather than by shearing. When hemolysate produced by the osmotic method without freezing was added to plasma and analyzed immediately, the ammonium levels were lower than when the hemolysate was frozen overnight before being added to the plasma pool. Ammonium levels were stable in unhemolyzed plasma left in contact with the cells for 1 h at room temperature or for 22 h when plasma was separated from cells and frozen. When plasma was stored in contact with the cells for 5 h, a similar increase in ammonium was observed in hemolyzed and unhemolyzed specimens. When plasma was stored in the absence of cells, the increases in ammonium were smaller than when plasma was stored in contact with the cells.

Studies

Study Purpose

The purpose of this study was to determine the effects of the method of obtaining hemolysate, the amount of hemolysis, and storage on plasma ammonium levels. Hemolysate produced by the osmotic method was frozen and thawed and then diluted to reach the desired levels of hemolysis before being added to plasma. Different levels of hemolysis were obtained using the shearing method by passing whole blood through a needle 0, 1, 2, 5, 8 or 15 times before centrifugation.

Summary of Findings:

Ammonium levels in plasma increased with increasing hemolysis. Higher levels of ammonium were measured in specimens when the added hemolysate was produced by shearing rather than by the osmotic method (with a freeze-thaw cycle), however, the rate of increase in ammonium levels with increasing hemolysis was greater when the hemolysate was produced by the osmotic method (with a freeze-thaw cycle) than by shearing. Including a freeze-thaw cycle for hemolysate produced by the osmotic method resulted in higher plasma ammonium levels than when hemolysate was produced without a freeze-thaw cycle. Ammonium levels were stable in unhemolyzed plasma left in contact with the cells for 1 h at room temperature or for 22 h when plasma was separated from cells and frozen. When plasma was stored in contact with the cells for 5 h, a similar increase in ammonium was observed in hemolyzed (by shearing) and unhemolyzed specimens. When plasma that was hemolyzed by shearing was stored in the absence of cells, the increases in ammonium were smaller than when plasma was stored in contact with the cells.

Biospecimens

Preservative Types

None (Fresh)

Diagnoses:

Not specified

Platform:

Analyte	Technology Platform
Small molecule	Clinical chemistry/auto analyzer

Pre-analytical Factors:

Classification	Pre-analytical Factor	Value(s)
Biospecimen Aliquots and Components	Hemolysis	Absent Distilled water-induced Fine needle aspiration-induced Freeze/thaw-induced Hemolysate added
Biospecimen Aliquots and Components	Biospecimen components	Hemolysis index of 27.6 Hemolysis index of 116.5 Hemolysis index of 219.7 Hemolysis index of 814.2 39 ug/dL ammonium 133 ug/dL ammonium
Storage	Time at room temperature	0 h 1 h 3 h 5 h
Storage	Freeze/thaw cycling	0 cycles 1 cycle

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