Clinical performance evaluation of total protein measurement by digital refractometry and characterization of non-protein solute interferences

Abstract

ObjectivesRefractometric methods to measure total protein (TP) in serum and plasma specimens have been replaced by automated biuret methods in virtually all routine clinical testing. A subset of laboratories, however, still report using refractometry to measure TP in conjunction with serum protein electrophoresis. The objective of this study was therefore to conduct a modern performance evaluation of a digital refractometer for TP measurement.Design and methodsPerformance evaluation of a MISCO Palm Abbe™ digital refractometer was conducted through device familiarization, carryover, precision, accuracy, linearity, analytical sensitivity, analytical specificity, and reference interval verification. Comparison assays included a manual refractometer and an automated biuret assay.ResultsCarryover risk was eliminated using a demineralized distilled water (ddH2O) wash step. Precision studies demonstrated overall imprecision of 2.2% CV (low TP pool) and 0.5% CV (high TP pool). Accuracy studies demonstrated correlation to both manual refractometry and the biuret method. An overall positive bias (+5.0%) was observed versus the biuret method. On average, outlier specimens had an increased triglyceride concentration. Linearity was verified using mixed dilutions of: a) low and high concentration patient pools, or b) albumin-spiked ddH2O and high concentration patient pool. Decreased recovery was observed using ddH2O dilutions at low TP concentrations. Significant interference was detected at high concentrations of glucose (>267 mg/dL) and triglycerides (>580 mg/dL). Current laboratory reference intervals for TP were verified.ConclusionsPerformance characteristics of this digital refractometer were validated in a clinical laboratory setting. Biuret method remains the preferred assay for TP measurement in routine clinical analyses.

Evaluation of 5 methods for diagnosing failure of passive transfer in 160 Holstein calves

“…The second method for measuring STP concentration was the biuret method using a commercially available kit (Pars Azmoon Co, Tehran, Iran) and an automated clinical chemistry analyzer (XL 200; Erba Mannheim, Mannheim, Germany). The automated biuret method assay is preferred for STP measurement in routine clinical analyses over refractometry …”

“…The automated biuret method assay is preferred for STP measurement in routine clinical analyses over refractometry. 29 was considered to be significant. Sample sizes for method comparison studies typically require at least 40 subjects from the population of interest.…”

“…The second objective was to determine whether digital Brix refractometry for serum provides an accurate, inexpensive, and rapid method for estimating IgG concentration in Holstein calves. The third objective was to compare the diagnostic accuracy of STP concentrations measured with a digital refractometer compared with that measured using the biuret laboratory method, which is regarded as the reference method for STP concentration …”

“…The third objective was to compare the diagnostic accuracy of STP concentrations measured with a digital refractometer compared with that measured using the biuret laboratory method, which is regarded as the reference method for STP concentration. 29 2 | MATERIALS AND METHODS 2.1 | Calf enrollment, feeding, and sampling Before blood sampling, each animal was examined by systemic and clinical inspection (respiratory rate, heart rate, and rectal temperature) and calves with vital signs outside the RIs were excluded from the study. Blood samples were obtained approximately 48 hours postcolostrum administration and 2 hours after the start of the morning feeding to minimize the potential confounding effects of feeding and changes in ambient temperature.…”

The effect of urea on refractometric total protein measurement in dogs and cats with azotemia

“…However, the conversion factor assumes the nonprotein solutes mentioned are within their RI . This is in contrast to the biuret assay, a more specific protein‐binding assay which is considered a more accurate method of measuring total proteins in small animals and is commonly used for routine chemistry panels …”