Storage: 30 days (after opening) at 2–8°C or 6 months (aliquotted) at –20°C.

Barcode labels are provided for use with the diluent. Before use, place an appropriate label on a 16 × 100 mm test tube, so that the barcodes can be read by the on-board reader.

L2HOZ: 3 labels

L2SUBM: Chemiluminescent Substrate

L2PWSM: Probe Wash

L2KPM: Probe Cleaning Kit

LRXT: Reaction Tubes (disposable)

L2ZT: 250 Sample Diluent Test Tubes (16 × 100 mm)

L2ZC: 250 Sample Diluent Tube Caps

CCCM: A bi-level, nonhuman serum- based Cardiac Marker Control Module, containing homocysteine as one of four different constituents.

Also required

Distilled or deionized water; test tubes; controls.

Assay Procedure

Note that for optimal performance, it is important to perform all routine maintenance procedures as defined in the IMMULITE 2000 Operator's Manual.

See the IMMULITE 2000 Operator's Manual for: preparation, setup, dilutions, adjustment, assay and quality control procedures.

Recommended Adjustment Interval: 4 weeks.

Quality Control Samples: Use controls or plasma or serum pools with at least two levels (low and high) of homocysteine.

Expected Values

Homocysteine levels can vary with age, gender, geographical area and genetic factors, therefore it is important for laboratories to establish their own reference ranges based on their local populations. Literature suggests a reference range of 5 – 15 µmol/L for adult males and females,11 but also notes that men tend to have higher levels than women, and that postmenopausal women tend to have higher levels than premenopausal.12

One hundred and twenty samples from apparently healthy adult male and female volunteers age 22–66 were analyzed

4

using the IMMULITE 2000 Homocysteine procedure. The samples were drawn in heparinized plasma tubes and kept on ice prior to separation of the plasma from the cells. The median value was 7.7 µmol/L, with a central 95% range of

5.0 – 12 µmol/L.

Consider these limits as guidelines only. Each laboratory should establish its own reference ranges.

Limitations

Specimens from patients who are on drug therapy involving S-adenosyl-methionine may show falsely elevated levels of homocysteine.

Although analysis of the parent compounds of carbamazepine, phenytoin, 6-azauridine, and anthopterin indicate no cross-reactivity, specimens obtained from patients treated with these drugs, as well as with methotrexate, nitrous oxide, and other anticonvulsants, should be interpreted with caution as these substances have been shown to interfere in some homocysteine assays.

Heterophilic antibodies in human serum can react with the immunoglobulins included in the assay components causing interference with in vitro immunoassays. [See Boscato LM, Stuart MC. Heterophilic antibodies: a problem for all immunoassays. Clin Chem 1988:34:27- 33.] Samples from patients routinely exposed to animals or animal serum products can demonstrate this type of interference potentially causing an anomalous result. These reagents have been formulated to minimize the risk of interference; however, potential interactions between rare sera and test components can occur. For diagnostic purposes, the results obtained from this assay should always be used in combination with the clinical examination, patient medical history, and other findings.

Performance Data

See Tables and Graphs for data representative of the assay's performance. Results are expressed in µmol/L. (Unless otherwise noted, all were generated on heparinized plasma samples.)

Calibration Range: 2 to 50 µmol/L.

IMMULITE 2000 Homocysteine (PIL2KHO-14, 2007-11-20)