ObjectivesRefractometers are commonly used to determine urine specific gravity (SG) in the assessment of hydration status and urine specimen validity testing. Few comprehensive performance evaluations are available demonstrating refractometer capability from a clinical laboratory perspective. The objective of this study was therefore to conduct an analytical validation of a handheld digital refractometer used for human urine SG testing.Design and methodsA MISCO Palm Abbe™ refractometer was used for all experiments, including device familiarization, carryover, precision, accuracy, linearity, analytical sensitivity, evaluation of potential substances which contribute to SG (i.e. “interference”), and reference interval evaluation. A manual refractometer, urine osmometer, and a solute score (sum of urine chloride, creatinine, glucose, potassium, sodium, total protein, and urea nitrogen; all in mg/dL) were used as comparative methods for accuracy assessment.ResultsSignificant carryover was not observed. A wash step was still included as good laboratory practice. Low imprecision (%CV, <0.01) was demonstrated using low and high QC material. Accuracy studies showed strong correlation to manual refractometry. Linear correlation was also demonstrated between SG, osmolality, and solute score. Linearity of Palm Abbe performance was verified with observed error of ≤0.1%. Increases in SG were observed with increasing concentrations of albumin, creatinine, glucose, hemoglobin, sodium chloride, and urea. Transference of a previously published urine SG reference interval of 1.0020–1.0300 was validated.ConclusionsThe Palm Abbe digital refractometer was a fast, simple, and accurate way to measure urine SG. Analytical validity was confirmed by the present experiments.

ObjectivesRefractometric methods to measure total protein (TP) in serum and plasma specimens have been replaced by automated biuret methods in virtually all routine clinical testing.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.

Introduction Plasma hemoglobin (Hb) is measured for assessment of in vivo and in vitro hemolysis. The objective of the present investigation was to conduct a method comparison of five quantitative and one semi‐quantitative Hb and H‐index (hemolysis index) assays to evaluate their performance measuring plasma Hb in clinical specimens. Methods One hundred and fourteen clinical specimens previously tested for plasma Hb using a laboratory‐developed spectrophotometric assay were also tested for Hb using a HemoCue Plasma/Low Hb assay (azide methemoglobin), a laboratory‐modified Pointe Scientific Hb assay (cyanmethemoglobin), tested for H‐index measurements using a Roche cobas c501, an Abbott Architect c8000, and a semi‐quantitative (binned) H‐index measurement on a Beckman AU5800. The reference result was defined as the median Hb score (median of all Hb or H‐index results). Results The laboratory‐developed spectrophotometric Hb assay and Roche H‐index methods mostly closely matched the median Hb score across all data, as well as for lower range median Hb score results ≤2.0 g/L. Two‐way frequency table analysis using an Hb (or H‐index) cutoff of 0.5 g/L (or 0.5 H‐index units) was then performed to compare methods to the median Hb score cutoff. The Beckman method had the highest accuracy at this cutoff, the Roche and Abbott methods had the highest positive predictive value (PPV), and the Beckman, HemoCue, and Pointe methods had the highest negative predictive value (NPV). Conclusions Plasma Hb and H‐index results vary by method. Laboratories should evaluate the performance characteristics of their respective assays when considering adoption of spectrophotometric or chemical methods for plasma Hb assessment.

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Objectives Nicotine (NIC) use during pregnancy can influence markers used in biochemical maternal serum screening. This study was designed to determine prevalence of disclosed tobacco smokers in our patient population and to compare disclosed tobacco smoking status with the presence of serum nicotine and a common tetrahydrocannabinol (THC) metabolite. Methods A deidentified dataset of disclosed smoking status for quadruple (Quad) screens was obtained. Residual serum submitted for Quad screens was obtained from frozen storage and analyzed for NIC and THC metabolites. Results Of specimens that had corresponding responses to the smoking history question on the patient history form, 7.2% (n = 1,783 of 24,611) specified that the patient was a tobacco smoker. Of the 271 specimens biochemically analyzed for NIC and THC metabolites, disclosed tobacco smokers had the highest prevalence of detectable NIC and THC metabolites. THC product use was most prevalent in patients categorized as probable tobacco smokers based on cotinine concentrations, as well as in younger patients. Conclusions Prevalence and concentration of NIC and THC metabolites vary based on disclosed tobacco smoker status. Biochemical testing may increase sensitivity for the identification of NIC and THC status over self-reporting.