Standard Operating Procedure
Subject
Index Number
Section
Subsection
Category
Contact
Last Revised
Gamma Glutamyltransferase (GGT) – Cobas c501/c502
Lab-4325
Laboratory
Chemistry
Departmental
Amy VanLin
1/17/2020
References
Required document for Laboratory Accreditation by the College of American Pathologists (CAP), Centers
for Medicare and Medicaid Services (CMS) and/or COLA.
Applicable To
Employees of the Gundersen Health System, Gundersen Moundview Hospital and Gundersen TriCounty Hospital laboratories.
INTENDED USE:
Detail
In vitro test for the quantitative determination of γ-glutamyltransferase (GGT) in human serum and
plasma on Roche/Hitachi cobas c systems.
PRINCIPLE:
Enzymatic colorimetric assay. γ-glutamyltransferase (GGT) transfers the γ-glutamyl group of L-γ-glutamyl
-3-carboxy-4-nitroanilide to glycylglycine. The amount of 5-amino-2-nitrobenzoate liberated is
proportional to the GGT activity in the sample. It is determined by measuring the increase in absorbance
photometrically.
CLINICAL SIGNIFICANCE:
γ-glutamyltransferase (GGT) is used in the diagnosis and monitoring of hepatobiliary diseases. Enzymatic
activity of GGT is often the only parameter with increased values when testing for such diseases, and is
one of the most sensitive indicators known. GGT is also a sensitive screening test for occult alcoholism.
Elevated GGT activities are found in the serum of patients requiring long-term medication with
phenobarbital and phenytoin.
In 2002, the International Federation of Clinical Chemistry (IFCC) recommended the standardized
method for determining GGT including optimization of substrate concentration, employment of NAOH,
glycylglycine buffer and sample start. The GGT liquid reagent follows the formulation recommendation
according to Szasz but was optimized for performance and stability. The assay is optionally standardized
against the original IFCC and Szasz method. The performance claims and data presented here are
independent from the standardization.
SPECIMEN:
Serum or heparinized plasma collected using standard sampling tubes or tubes containing separating
gel.
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Standard Operating Procedure
Stability: 7 days at 15-25oC, 7 days at 2-8oC, 1 year at -20oC ±5°C.
Centrifuge samples containing precipitates before performing the assay. Universal precautions apply.
REAGENTS / MATERIALS:
γ-Glutamyltransferase ver.2 Standardized against Szasz, 400 tests – the reagent cassette is labeled as
GGT-2. R1 is in position B and R2 is in position C. Ready to use.
R1 - TRIS: 492 mmol/L, pH 8.25; glycylglycine: 492 mmol/L; preservative; additive
R2 - L-γ-glutamyl-3-carboxy-4-nitroanilide: 22.5 mmol/L; acetate: 10 mmol/L, pH 4.5; stabilizer;
preservative
Diluent NaCl 9%, 50 mL – the diluent cassette is labeled as NACL.
Precautions and Warnings: For in vitro diagnostic use. Exercise the normal precautions required for
handling all laboratory reagents. Disposal of all waste material should be in accordance with local
guidelines.
Storage:
γ-Glutamyltransferase ver.2 Standardized against Szasz - Store at 2-8°C.
Diluent NaCl 9% - Store at 2-8°C.
Stability:
γ-Glutamyltransferase ver.2 Standardized against Szasz - Unopened at 2-8°C - up to the stated expiration
date. On-board in use and refrigerated on the c501c502 – 12 weeks.
Diluent NaCl 9% - Unopened at 2-8°C - up to the stated expiration date. On-board in use and
refrigerated on the c501/c502 – 12 weeks.
EQUIPMENT / INSTRUMENTATION:
Roche c501/c502 analyzer - Refer to the Operator’s Manual for operating instructions, maintenance,
and troubleshooting.
Calibration: This method has been standardized against the original IFCC formulation (2002) and against
the GGT method published by Persijn and van der Silk (1976), respectively. Calibration mode: Linear, 2point calibration.
Calibrators: C.f.a.s. Use deionized water as zero calibrator.
Preparation: Add 3.0 mL of DI water and let stand for 30 minutes. Mix carefully, avoiding foam
formation.
Stability: 2 days at 2-8°C
Calibration Frequency: Calibration must be performed once per reagent lot using fresh reagent (i.e. not
more than twenty-four hours since the reagent pack was registered on the analyzer). Renewed
calibration is recommended as follows:
1. If necessary after instrument service or repair
2. If dictated by quality control results
3. After regent lot change
QUALITY CONTROL:
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Standard Operating Procedure
BioRad Unassayed Chemistry controls, levels 1 and 2
Preparation: Ready to use
Storage/Stability: Stable until expiration date when stored unopened at -20°C to -70°C, once thawed,
opened and stored tightly capped at 2-8°C, this product will be stable for 5 days.
This product is shipped under frozen conditions.
Refer to Lab-4405 Quality Control Criteria for Chemistry for interpretation of QC. Two levels of quality
control should be performed at a minimum:
1. Once every twenty-four hours.
2. If a new pack of reagent is put into use.
3. If a calibration is performed.
Implementation
Refer to the Cobas 6000/8000 Operator’s Manual Located in the chemistry department.
PROCEDURE NOTES:
Results are reported to the nearest whole number in U/L.
AMR (Analytical Measurement Range): 3- 1200 U/L. The extended measuring range with with the
automatic rerun function in the Decrease mode (1:11) of the analyzer is 3-13200 U/L. Results from the
diluted sample, utilizing the rerun function, are automatically multiplied by a factor of 11.
Values below 3 are reported as <3 U/L.
Values above 13200 are reported as >13,200 U/L.
CALCULATIONS:
The COBAS 6000/8000 system automatically calculates the GGT activity of each sample.
INTERPRETATION:
Expected Range: Men 8-61 U/L
Women 5-36 U/L
LIMITATIONS:
Hemolysis: No significant interference up to an H index of 200 (approximate hemoglobin concentration:
0.2 g/dL).
Icterus: No significant interference up to an I index of 50 for conjugated and 20 for unconjugated
bilirubin (approximate conjugated bilirubin concentration: 50 mg/dL and approximate unconjugated
bilirubin concentration: 20 mg/dL).
Lipemia: No significant interference up to an L index of 1500. There is poor correlation between the L
index (corresponds to turbidity) and triglycerides concentration.
See package insert for additional interference and cross-reactivity studies. The results should always be
assessed in conjunction with the patient’s medical history, clinical examination and other findings.
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Standard Operating Procedure
Special wash Requirements: The determination of certain analytes interferes with this assay requiring a
special wash step. Refer to the NaOHD/SMS/SmpClin1+2/SCCS method sheet and the operator manual
for further instructions.
Cobas c502 analyzer: All special wash programming necessary for avoiding carry-over is available via the
cobas link, manual input is not required.
REVIEW AND CHANGES:
This document and all attached forms should be reviewed optimally on an annual basis, with 2 years as
the maximum review date. Review will be done by the Technical Leader, Supervisor, Manager, Medical
Director or designated person. Changes require retyping the document or form and review by the
Medical Director.
REFERENCES:
1.
2.
3.
4.
Roche γ-Glutamyltransferase ver.2 Standardized against IFCC / Szasz package insert
Roche C.f.a.s. package insert
Roche Diluent NaCl 9% package insert
Roche Cobas 6000/8000 Operator’s Manual
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