Salicylate

Serum or plasma

2 mL

0.6 mL

Red-top tube or green-top (heparin) tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.

Liquid chromatography/tandem mass spectrometry (LC/MS-MS)

Therapeutic (anti-inflammatory): 30−250 μg/mL

Optimal sampling time after dosage is two to six hours. Serum half-life is two to three hours on low-dose therapy, 15 to 30 hours on high-dose treatment. Optimal resampling time after change in dosage is six hours. In patients on chronic therapy, small dose changes may produce disproportionate changes in serum level. Use of antacids, which increase renal excretion, can lower serum levels. Steady-state concentrations for an individual patient are not adequately predicted from nomograms or standard dose schedules. In salicylate poisoning, the following symptoms may occur: initial alkalosis followed by acidosis in the blood, ketosis, and possible elevated plasma glucose. Glucose should be measured when levels >250 μg/mL are detected. Salicylate can be done on urine or gastric juice.

The Done nomogram is used to estimate blood level and prognosis following a single dose ingestion. The level measured four hours or more following ingestion is plotted. Specimens drawn earlier may not reflect the peak. The nomogram is not useful when accumulation over several ingestions exists. Urine pH and volume hourly are advocated with plasma pH, potassium and other electrolytes, prothrombin time, AST, ALT, serum bilirubin, and arterial blood gases for care of serious pediatric salicylate poisoning.¹

Salicylate hepatitis, usually at blood levels of 200−250 μg/mL, occurs. Salicylates are believed to play a role in the hepatonecrosis of Reye syndrome in children. They are no longer recommended for use in children.