An investigation of enzymatic creatinine interference in a patient receiving dopamine and dobutamine

Highlights

• Dopamine or dobutamine specimen contamination may produce interference with enzymatic creatinine measurement procedures.

• Peripherally inserted central catheter specimen line draws are not recommended during a dopamine and dobutamine infusion.

• A siphoning mechanism potentially contaminates specimens during simultaneous collection while the infusion pump running.

Abstract

Background

A laboratory investigation was initiated after a renal failure patient had a 2.18 mg/dL decrease in serum creatinine, which was not explained through medical intervention. The investigation revealed specimens providing questionably low results had been collected from a peripherally inserted central catheter (PICC) line.

Methods

Patient specimens and serum pools were analyzed by the Siemens Vista enzymatic creatinine measurement procedure. A simulation of the patient's infusion protocol examined potential PICC line carryover and specimen collection technique.

Results

A simultaneously collected specimen set, arterial line and PICC line, yielded a difference of 1.86 mg/dL. Infusion and collection simulation studies suggested the most likely scenario was the infusion pump was not shut off while the specimen collection occurred and contaminated the specimen.

Conclusion

Providers should be aware of erroneously low creatinine results when administering catecholamine drugs and collecting specimens through the same catheter. The mechanism of specimen contamination is consistent with a siphoning effect from one lumen to the other during collection with the infusion pumps still running.

Introduction

Serum creatinine is a biomarker for estimating glomerular filtration rate (eGFR) in patients [1]. Serum creatinine results are input into estimating equations and provide clinicians with an assessment of renal function. Two laboratory creatinine measurement procedures are the Jaffe and the enzymatic reagent systems. The Jaffe reagents utilize picric acid to produce a colorimetric response and enzymatic reagents employ enzymes throughout the reaction. The Jaffe reaction's non-specificity is well documented [[2], [3], [4], [5]]. Given these analytical specificity issues, laboratories are moving to enzymatic creatinine measurement procedures, which are viewed as more creatinine specific.

Reports of enzymatic creatinine reagents providing falsely low results when patients are receiving dopamine and or dobutamine have been published [[6], [7], [8], [9], [10], [11], [12]]. Karon et al. proposed two separate chemical mechanisms for this interference, both producing negative interference [9]. One was dopamine in the presence of peroxide reacts with assay reagents to produce a chromophore with a smaller absorptivity and falsely lowers signal. The other is in the presence of peroxidase, dobutamine reacts with and depletes peroxide to levels inhibiting chromophore generation.

This study was pursued after an inpatient with renal failure had a 2.18 mg/dL decrease in serum creatinine with no medical intervention. The initial result was 4.25 mg/dL and 6 h later was 2.07 mg/dL. All creatinine measurements were obtained using the Siemens Dimension® Vista 1500 employing enzymatic creatininase reagents. Repeat specimen analysis on the laboratory's 2nd Vista instrument provided the same result. Further investigation revealed the specimens providing questionable results were collected from a peripherally inserted central catheter (PICC) line. During the third PICC line collection, a simultaneous arterial line specimen collection was analyzed by the Vista and provided values consistent with previous.

Specimen collection protocol, drug carryover studies and in vitro drug delivery simulations using the patient's same PICC line model and infusion rate were investigated.