Impact of Unconjugated estriol (uE3) assay interference on prenatal screening tests

BACKGROUND

Unconjugated estriol (uE3) is an important biomarker in second trimester prenatal screening. Previous studies from our laboratory identified rare interference in the Beckman uE3 assay due to anti-ALP antibodies, which could be mitigated with a scavenger or heat-inactivated ALP (hALP). In the current study, 160 de-identified patient samples previously submitted for the Quad screen with low uE3 multiples of the median (MoM ≤0.50) were investigated for potential interference.

METHODS

A reagent pack spiking strategy with hALP was employed to understand if the interference could be identified and mitigated in a scalable manner. The 160 samples were measured using uE3 lot #920861 previously known to be subject to interference, lot #920861 spiked with hALP, and the vendor reformulated lot #922579. Samples were suspected to have interference if the percent difference in uE3 measurements was >50%. Pseudo-risks were calculated using a test patient environment to understand the screening impact due to the change in uE3 result.

RESULTS

Seventeen of the 160 samples had uE3 results that were >50% different between the hALP spiked and non-spiked reagent pack. Both original lot #920861 with hALP and reformulated lot #922579 identified the same 17 patients as having interference in lot #920861. Analysis of screening risks using a test patient environment showed that assay interference could result in false positives for one trisomy 21 and three trisomy 18 post-test risk calculations.

CONCLUSION

Our experiment of reagent pack spiking with hALP produced similar uE3 results to a reformulated reagent designed to address potential interference, demonstrating that this is a feasible strategy to screen for interference in a scalable manner. The vendor-provided reformulation addressed anti-ALP interference and improved the performance of the screen.

Tobacco and Cannabis Use During Pregnancy

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.

Plasma hemoglobin: A method comparison of six assays for hemoglobin and hemolysis index measurement

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.

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

OBJECTIVES

Refractometric 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 METHODS

Performance 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.

RESULTS

Carryover 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.

CONCLUSIONS

Performance 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 and analytical validation of a handheld digital refractometer for urine specific gravity measurement

Objectives

Refractometers 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 methods

A 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.

Results

Significant 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.

Conclusions

The Palm Abbe digital refractometer was a fast, simple, and accurate way to measure urine SG. Analytical validity was confirmed by the present experiments.

Alternative uses for the haemostatic vascular sheath

The haemostatic vascular sheath has several non-vascular applications in interventional radiology. It is used to preserve access to an organ (i.e. contrast can be introduced without removing catheters and guidewires). There are also advantages regarding patient comfort and safety. Three such applications are described.

Transcolonic retrograde ureteric catheterization assisted by 3-D computed tomography

A 42-year-old woman had bladder exstrophy at birth, treated by ureterocolic anastomosis of her single kidney. She suffered recurrent hyperammonaemia, leading to comas, but refused an ileal conduit. During her most recent coma, it was decided to divert her urine to test whether this would reduce hyperammonaemia: this was accomplished by transcolonic retrograde catheterization of the ureter. This was only possible after computed tomography ureterography to show the ureterocolic anastomosis.

Technical report: A low cost technique for vessel sizing in angioplasty

Vessel measurement in angiography is important for balloon and stent sizing. The most accurate techniques involve calibrating the angiographic image with a catheter with radioopaque markers, but these are expensive. A new method of vessel sizing for angioplasty and stenting is described: the guidewire is moved within the vessel through a set distance, and this movement is shown by digital subtraction. Testing with phantoms shows this to be simple, accurate and reproducible.

Fatal encephalitis due to novel paramyxovirus transmitted from horses

BACKGROUND

In September, 1994, an outbreak of severe respiratory disease affected 18 horses, their trainer, and a stablehand in Queensland, Australia. Fourteen horses and one human being died. A novel virus was isolated from those affected and named equine morbillivirus (EMV). We report a case of encephalitis caused by this virus.

FINDINGS

A 35-year-old man from Queensland had a brief aseptic meningitic illness in August, 1994, shortly after caring for two horses that died from EMV infection and then assisting at their necropsies. He then suffered severe encephalitis 13 months later, characterised by uncontrolled focal and generalised epileptic activity. Rising titres of neutralising antibodies to EMV in the patient's serum at the time of the second illness suggested an anamnestic response. Distinctive cortical changes were shown on magnetic resonance neuroimaging and histopathological examination of the brain at necropsy. Immunohistochemistry and electronmicroscopy of brain tissue revealed pathology characteristic of the earlier cases of EMV infection. PCR on cerebrospinal fluid taken during the second illness, brain tissue, and serum retained from the original illness resulted in an amplified product identical to that previously described from EMV.

INTERPRETATION

The results of serology, PCR, electronmicroscopy, and immunohistochemistry strongly suggest that EMV was the cause of this patient's encephalitis, and that exposure to the virus occurred 3 months before the fatal illness.

Needle thoracocentesis in tension pneumothorax: insufficient cannula length and potential failure

Advanced Trauma Life Support guidelines recommend the use of a cannula 3 to 6 cm long to perform needle thoracocentesis for life-threatening tension pneumothorax. The chest wall thickness in the 2nd intercostal space, mid-clavicular line, was determined by ultrasound in 54 patients aged 18 to 55 years, and ranged from 1.3 to 5.2 cm (mean 3.2 cm). In thirty-one patients (57 per cent) the chest-wall thickness (CWT) was greater than 3 cm, the minimum recommended cannula length, although in only two (4 per cent) was it greater than 4.5 cm, the length of cannula commonly used in the UK. As a 3 cm cannula would fail to reach the pleural cavity in over half of patients, we suggest that the recommended shortest length be increased to 4.5 cm. Unsuccessful needle thoracocentesis using a 4.5 cm cannula should be followed immediately by insertion of a longer cannula or a definitive chest drain.

Balloon rupture and stenting for pelviureteric junction obstruction: abolition of waisting is a prognostic marker

Endoballoon rupture and stenting was performed on 26 patients with pelviureteric junction obstruction. Follow-up was for a mean of 21.4 months (range 3 to 44 months), during which 16 patients (64%) were asymptomatic and the symptoms of eight (30%) recurred; two were lost to follow-up. When waisting of the balloon was observed and seen to resolve during the balloon inflation, the outcome was successful in 75% of patients, compared to only 43% if this was not observed. Balloon rupture and stenting is a useful alternative to pyeloplasty, but has a lower success rate. Major complications were rare. The abolition of waisting is an important prognostic sign.