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Test Code LAB5081/10818/MCAFF Caffeine, Serum

Important Note

Send Outs - Mayo

On 02/25/2020, this test replaced LAB4835/10523/CAFN.

Specimen Required

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions:

1. Serum gel tubes should be centrifuged within 2 hours of collection.

2. Red-top tubes should be centrifuged and the serum aliquoted into a plastic vial within 2 hours of collection.

Method Name

Enzyme Multiplied Immunoassay Technique (EMIT)

Reporting Name

Caffeine, S

Specimen Type


Reject Due To

Gross hemolysis Reject

Day(s) and Time(s) Performed

Monday through Saturday

Analytic Time

Same day/1 day

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
CAFF Caffeine, S In Process


Result ID Test Result Name Result LOINC Value
8754 Caffeine, S 3422-3

Secondary ID


Useful For

Monitoring caffeine therapy in neonates


Assessing caffeine toxicity in neonates

Clinical Information

Caffeine is used to treat apnea of prematurity that occurs in newborn infants, the most frequent complication seen in the neonatal nursery.


In neonates, caffeine has a half-life that ranges from approximately 3 to 4 days, which is much longer than in adults (typically 4-6 hours) due to the immaturity of the neonatal liver. This requires that small doses be administered at much longer intervals than would be predicted based on adult pharmacokinetics.


The volume of distribution of caffeine is 0.8-0.9 L/kg (infants) or 0.6 L/kg (adults) and the drug is approximately 36% protein bound.


Toxicity observed in neonates is characterized by central nervous system and skeletal muscle stimulation and bradycardia. These symptoms are seen in adults at lower levels than in neonates, suggesting that neonates have much greater tolerance to the drug.


Optimal pharmacologic response occurs when the serum level is in the range of 8.0 to 20.0 mcg/mL.


Toxicity in neonates and adults may be seen when the serum level is above 20.0 mcg/mL.


This assay is not intended to detect levels in adults.

Clinical Reference

1. Milone MC, Shaw LM: Therapeutic drugs and their management. In: Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, Elsevier; 2018:800-831

2. Brunton LL, Hilal-Dandan R, Knollmann BC, eds. Goodman and Gilman's: The Pharmacological Basis of Therapeutics. McGraw-Hill; 2018

3. Ou CN, Frawley VL: Concurrent measurement of theophylline and caffeine in neonates by an interference-free liquid-chromatographic method. Clin Chem. 1983;29:1934-1936

Method Description

The enzyme-multiplied immunoassay technique (EMIT) assay is a homogeneous enzyme immunoassay technique used for the analysis of specific compounds in biological fluids. The assay is based on competition between drug in the sample and drug labeled with the enzyme glucose-6-phosphate dehydrogenase (G6PD) for antibody binding sites. Enzyme activity decreases upon binding to the antibody, so the drug concentration in the sample can be measured in terms of enzyme activity. Active enzyme converts oxidized nicotinamide adenine dinucleotide (NAD) to NADH, resulting in an absorbance change that can be measured spectrophotometrically. Endogenous serum G6PD does not interfere because the coenzyme functions only with the bacterial (Leuconostoc mesenteroides) enzyme employed in the assay.(Package insert: Seimens Caffeine Reagent. Seimens Healthcare Diagnostics, Ltd; 03/2015)

Specimen Retention Time

2 weeks

Specimen Minimum Volume

0.25 mL

Reference Values

Therapeutic: 8.0-20.0 mcg/mL

Critical value: ≥30.0 mcg/mL


If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Frozen (preferred) 28 days
  Ambient  72 hours
  Refrigerated  72 hours