Heparin Interference Research Articles

Heparin interference in the measurement of gamma-glutamyltransferase activity with the Scandinavian and the IFCC recommended method.

Heparin in heparinized plasma, and when added to serum, is shown to interfere markedly in the assay of gamma-glutamyltransferase when using the method recommended by both the Scandinavian Society for Clinical Chemistry and Clinical Physiology, and the Expert Panel on Enzymes of IFCC. The effect is also revealed as an apparent sample blank reaction (donor substrate omitted). It decreases as the time of first reading is increased, and it can be reduced or nearly abolished by addition of extra NaCl (increasing the ionic strength). Evidence is presented suggesting that this photometric interference is caused by turbidity due to complex formation between heparin and various plasma proteins. Fibrinogen appears to be one of the main proteins involved. It is concluded that in general care should be taken when using heparinized plasma in enzyme assays, and that heparin should only be used when specific testing has ruled out photometric interference.

Heparin interferes with the radioenzymatic and homogeneous enzyme immunoassays for aminoglycosides.

Heparin interferes with measurement of aminoglycosides in serum by biological, radioenzymatic, and homogeneous enzyme immunoassay techniques, but not with radioimmunoassay. At concentrations greater than or equal to 10(5) and greater than or equal to 3 X 10(6) USP units/L, respectively, it interferes with the radioenzymatic assay by inhibiting the gentamicin 3-acetyltransferase (EC 2.3.1.60) and kanamycin 6'-acetyltransferase (EC 2.3.1.55) enzymes used in the assay. It interferes with the homogeneous enzyme immunoassays for gentamicin and tobramycin (at concentrations greater than or equal to 10(5) and greater than or equal to 10(4) USP units/L, respectively), but not with the commercially available homogeneous enzyme immunoassays for other drugs. Heparin interference with the homogeneous enzyme immunoassay for aminoglycosides requires both the heparin polyanion and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) bound to a cationic aminoglycoside. This interference can be reproduced with dextran sulfate (but not dextran), and does not occur with free enzyme (glucose-6-phosphate dehydrogenase) alone. We describe how heparin interferes with these two assays and demonstrate interference at heparin concentrations that may be present in intravenous infusions or in seriously underfilled blood-collection tubes.

Heparin interference in creatine kinase assays.

Heparin interference in creatine kinase assays.

An improved method for plasma fibrinogen based on thrombin time measurement

Methods for plasma fibrinogen based on thrombin time are technically simple, rapid, and sensitive, although “false low” results may occur due to heparin interference. The present modification incorporates Polybrene into buffer to eliminate this heparin interference. The proposed method shows excellent agreement with a reference procedure based on protein, and excellent day-to-day precision (C.V. 3.5%). The present method is easily adaptable to semi-automated measurements.

Improved micromethod for plasma fibrinogen unaffected by heparin therapy.

An improved micromethod for plasma fibrinogen, based on the Ellis-Stransky thrombin-clot density procedure, is presented. Modifications includes: (1) addition of Polybrene eliminates heparin interference; (2) measurement of absorbance at 340 nm provides improved sensitivity at low fibrinogen levels as well as with small volumes of plasma (40 mul.); (3) higher concentration of thrombin reduces the incubation time. Plasma fibrinogen by the proposed method compares well with a reference procedure based on total clottable protein (coefficient of correlation 0.99).