The analytical change in plasma creatinine that constitutes a biologic/physiologic change.

PURPOSE: Accurate and precise measurements of creatinine are necessary to evaluate changes in kidney function related to a decreased glomerular filtration rate (GFR). When serial measurements of creatinine are monitored in an individual, it is useful to know what magnitude of an analytical change in creatinine indicates a true physiologic/biologic change in plasma creatinine that might warrant clinical intervention. METHODS: We compared results between three different methods for creatinine using large chemistry analyzers, two based on alkaline picrate (AP1 and AP2), and one based on dry-slide enzymatic conversion (ENZ). On each of three different segments or days of the study spaced 1-2months apart, we selected 10 different plasma samples having creatinine concentrations ranging from about 0.5mg/dL to 4.5mg/dL (44 to 400µmol/L). Each sample was analyzed in triplicate on each of two same-model analyzers at each institution, then from this data we determined the precision of each model of analyzer. The within-instrument precision of each analyzer was evaluated from the differences between the triplicate results on each sample by each analyzer (mean and SD of the differences). The between-instrument precision was evaluated as the differences between results on the same sample (1, 2, 3, etc.) analyzed on different analyzers of the same model (A and B). This between-analyzer precision data was used to determine both the range and mean±2SD of the differences that could be used to indicate that greater changes in creatinine concentrations would represent a biologic change. RESULTS: The within-instrument precision was best for the ENZ method in comparison to the two alkaline picrate rate methods. The between-instrument precision of the 90 consecutive measurements (30 samples×triplicate analyses) between the same-model analyzers were (mean and SD of differences in mg/dL): -0.018 and 0.029 (ENZ); 0.016 and 0.11 (AP1), and -0.058 and 0.071 (AP2). CONCLUSIONS: While all three of the creatinine methods studied had good precision, the ENZ method had the best precision, such that a change of 0.07mg/dL (6µmol/L) in serial creatinine concentrations up to 1.5mg/dL on a patient could indicate a biologic change had occurred. For the alkaline picrate methods, a measured change of creatinine of 0.23mg/dL for AP1 or 0.11mg/dL for AP2 would indicate that a physiologic change in serum/plasma creatinine has occurred. While a definite biologic change may simply represent daily variations, detecting a biologic change in creatinine more rapidly could impact the ability of creatinine to detect early and clinically significant changes in renal function.

A primer on definitive gas and liquid chromatography drug testing: What clinicians need to know.

OBJECTIVE: To describe the differences between mass spectrometry technologies and compare and contrast them with immunoassay techniques of urine drug testing (UDT). Highlight the potential importance of the differences among these technologies for clinicians so as to allow them make decisions in their use in patient care. METHODS: Review of mass spectrometry techniques, including gas chromatography, liquid chromatography, and time-of-flight techniques. RESULTS: The potential clinical implications of these technologies stemming from their scope and accuracy are presented. SIGNIFICANCE: UDT is an important clinical tool, though there are differences in technology and testing processes with important implications for clinical decision making. It is crucial, therefore, that clinicians have an understanding of the technologies behind the tests they order, so that their interpretation and use of results are based on an understanding of the strengths and weaknesses of the technologies used.

Associations between Body Composition, Hormonal and Lifestyle Factors, Bone Turnover, and BMD.

BACKGROUND: The relative importance of body composition, lifestyle factors, bone turnover and hormonal factors in determining bone mineral density (BMD) is unknown. We studied younger postmenopausal women to determine whether modifiable or nonmodifiable risk factors for osteoporosis have stronger associations with BMD. METHODS: In multivariable linear regression models, we tested associations between non-bone body composition measures, self-reported measures of physical activity and dietary intake, urinary N-telopeptide (NTx), sex hormone concentrations, and BMD in 109 postmenopausal women aged 50 to 64 years, adjusting for current hormone therapy use and clinical risk factors for low BMD. Lean mass, fat mass and areal BMD (aBMD) at the lumbar spine, femoral neck, total hip and distal radius were measured using dual energy X-ray absorptiometry. RESULTS: Higher body weight and self-reported nonwhite race were independently associated with higher aBMD at the lumbar spine, femoral neck, total hip and distal radius. Lean and fat mass were not independently associated with aBMD. Older age and higher urinary NTx were independently associated with lower aBMD at the distal radius but not at weight-bearing sites. Sensitivity analyses demonstrated lack of an independent association between total daily protein or calorie intake and BMD. CONCLUSIONS: BMD, weight and race were the most important determinants of aBMD at all sites. Older age and higher bone turnover were independently associated with lower aBMD at the distal radius. In a limited analysis, self-reported physical activity, dietary protein and calorie intake were not associated with aBMD after adjustment for the other variables.

Evaluation of high resolution gel ß(2)-transferrin for detection of cerebrospinal fluid leak.

BACKGROUND: Cerebrospinal fluid (CSF) leaks are potentially life-threatening conditions that can be diagnosed by detection of ß(2)-transferrin using protein electrophoresis. Another less commonly available test is ß-trace protein quantitation using immunoassay. The objectives of this study were to evaluate a new immunofixation-based ß(2)-transferrin test for detection of CSF leaks and to compare it to an existing agarose gel electrophoresis test and ß-trace protein immunoassay. METHODS: For method comparison, 63 consecutive samples from physician-ordered ß(2)-transferrin tests were analyzed using two different electrophoresis methods, agarose gel fractionation followed by acid-violet staining, and high resolution agarose gel electrophoresis followed by ß(2)-transferrin immunofixation. A subset of samples (16/63) were analyzed for ß-trace protein. Results were compared against patient chart data for the presence of a CSF leak. Additional studies were performed to assess the stability, detection limit, and analytical specificity of the ß(2)-transferrin immunofixation test. RESULTS: The ß(2)-transferrin immunofixation test had a sensitivity of 100 % (40/40) and specificity of 71 % (12/17) for detection of CSF leaks. By comparison, the agarose gel test had a sensitivity of 87 % (35/40) and specificity of 94 % (16/17). ß-trace protein had a sensitivity of 100 % (10/10) and specificity of 86 % (5/6). Serum and saliva could be differentiated from CSF by the ß(2)-transferrin immunofixation test based on their migration patterns. However, whole blood samples appeared positive for ß(2)-transferrin at a threshold of ~ 4 g/L hemoglobin. At a cut-off of 3 mg/L, ß-trace protein was increased in 10/10 cases with documented CSF leak and in 1/6 patients without CSF leak. CONCLUSIONS: Both the new immunofixation test for ß(2)-transferrin and the ß-trace protein were effective at detecting CSF leaks. Users of the ß(2)-transferrin immunofixation test should be cautioned against interpreting samples with blood contamination.

Unexpected interference of baby wash products with a cannabinoid (THC) immunoassay.

OBJECTIVES: The results of newborn drug screening have far-reaching impact not only in healthcare, but also in the legal domain. Therefore, the accuracy of these results cannot be undervalued. When false positive cannabinoid (THC) screening results for this population were suspected at our institution, a multidisciplinary approach was initiated to evaluate the screening process for any pre-analytical or analytical sources of error or interference. DESIGN AND METHODS: Mixtures of drug-free urine with various commercial products and materials that commonly contact newborns in our nursery were prepared and tested using the immunoassay screening methods in our laboratory. Additional commercial products were similarly tested; and when available, individual surfactants common to the interfering products were also evaluated. RESULTS: Addition of Head-to-Toe Baby Wash to drug-free urine produced a dose dependent measureable response in the THC immunoassay. Addition of other commercially available baby soaps gave similar results, and subsequent testing identified specific chemical surfactants that reacted with the THC immunoassay. CONCLUSION: We have identified commonly used soap and wash products used for newborn and infant care as potential causes of false positive THC screening results. Such results in this population can lead to involvement by social services or false child abuse allegations. Given these consequences, it is important for laboratories and providers to be aware of this potential source for false positive screening results and to consider confirmation before initiating interventions. Most importantly, we demonstrate the need for active involvement in the "total testing process," as sources of error are not confined to the laboratory walls.

Follicle-stimulating hormone is independently associated with lean mass but not BMD in younger postmenopausal women.

PURPOSE: Increased follicle-stimulating hormone (FSH) has been associated with lower bone mineral density (BMD) in animal models and longitudinal studies of women, but a direct effect has not been demonstrated. METHODS: We tested associations between FSH, non-bone body composition measures and BMD in 94 younger (aged 50 to 64 years) postmenopausal women without current use of hormone therapy, adjusting for sex hormone concentrations and clinical risk factors for osteoporosis. Lean mass, fat mass and areal BMD (aBMD) at the spine, femoral neck and total hip were measured using dual energy X-ray absorptiometry (DXA). Volumetric BMD (vBMD) was measured at the distal radius using peripheral quantitative computed tomography (pQCT). RESULTS: FSH was inversely correlated with lean and fat mass, bioavailable estradiol, spine and hip aBMD, and vBMD at the ultradistal radius. In the multivariable analysis, FSH was independently associated with lean mass (ß=-0.099, p=0.005) after adjustment for age, race, years since menopause, bioavailable estradiol, bioavailable testosterone, LH, PTH, SHBG and urine N-telopeptide. FSH showed no statistically significant association with aBMD at any site or pQCT measures at the distal radius in adjusted models. Race was independently associated with aBMD, and race and urine N-telopeptide were independently associated with bone area and vBMD. CONCLUSIONS: After adjustment for hormonal measures and osteoporosis risk factors, higher concentrations of FSH were independently associated with lower lean mass, but not with BMD. Previously reported correlations between FSH and BMD might have been due to indirect associations via lean mass or weight.

The evolution of mass spectrometry in the clinical laboratory.

Clinical laboratories around the world are recognizing the power of mass spectrometry. This technique, especially when coupled to gas chromatography or liquid chromatography, is revolutionizing the analysis of many analytes. Unlike many other techniques which measure one analyte at a time, these techniques can measure multiple analytes (>40) at one time. In recent years the scope of testing using these techniques has expanded from toxicological purposes to newborn screening to hormones, proteins, and enzymes. It is not uncommon any more to see mass spectrometry being used in the routine clinical laboratories.

Monitoring of mycophenolate acid in serum or plasma using LC tandem mass spectrometry.

Therapeutic drug management of patients receiving mycophenolic mofetil or mycophenolate sodium using mycophenolic acid (MPA) concentrations is controversial. Considered to be less toxic compared to many of the other drugs used in immunosuppression regimens, MPA is not tolerated by all patients. For these patients, monitoring is useful in achieving desired therapeutic targets, reducing adverse effects, and individualizing dosing. We describe an LC-MS-MS that permits the measurement of MPA and 7-O-glucuronide mycophenolic acid (MPAG) in serum or plasma.

A case of hook effect in the serum free light chain assay using the Olympus AU400e.

We describe a case where a woman with an IgG lambda monoclonal gammopathy had an undetectable serum free lambda light chain due to antigen excess. The patient had a three year history of multiple myeloma and initially presented with an elevated serum free lambda light chain. The serum free lambda light chain concentration increased over the course of several months to >4000 mg/L (reference interval 5.7-26.3 mg/L) and then suddenly dropped to <3.0 mg/L. Paradoxically, during this time the monoclonal IgG lambda concentration measured using serum protein electrophoresis increased from 44 to 59 g/dL. Serial dilution of the patient's serum specimen revealed that the serum free lambda light chain was actually 3130 mg/L. This case represents an example of antigen excess or 'hook effect' using the serum free light chain assay.

Performance comparison of capillary and agarose gel electrophoresis for the identification and characterization of monoclonal immunoglobulins.

The objective of this study was to compare gel- and capillary-based serum protein electrophoresis methods to identify and characterize monoclonal immunoglobulins (M proteins). Five reviewers interpreted 149 consecutively ordered serum specimens following agarose gel electrophoresis (AGE), capillary electrophoresis (CE), immunofixation electrophoresis (IFE), and subtraction immunotyping (IT). As a screening test for detecting M proteins, AGE and CE displayed similar sensitivity (91% and 92%, respectively). CE was less specific (74%) than AGE (81%). An analysis of interinterpreter agreement revealed that interpretations were more consistent using gel-based methods than capillary-based methods, with 80% of the gel interpretations being in complete (5/5) agreement compared with 67% of the capillary interpretations. After implementing the capillary-based methods, the number of tests per reportable result increased (from 1.58 to 1.73). CE is an analytically suitable alternative to AGE, but laboratories implementing it will need to continue IFE testing to characterize all M proteins detected by CE.

Executive summary. The National Academy of Clinical Biochemistry Laboratory Medicine Practice Guideline: evidence-based practice for point-of-care testing.

BACKGROUND: Point-of-care testing (POCT) is clinical laboratory testing conducted close to the site of patient care. POCT has the potential to provide faster test results and therapeutic intervention with improved patient outcomes. However, when over-utilized or used inappropriately POCT results can be misleading and increase healthcare costs. METHODS: The National Academy of Clinical Biochemistry developed evidence-based Laboratory Medicine Practice Guidelines for POCT. RESULTS: These Laboratory Medicine Practice Guidelines systematically review the scientific literature relating POCT to clinical outcomes and offer recommendations to improve the clinical utility of POCT. CONCLUSIONS: These guidelines will be useful to clinicians considering the addition of POCT, to those that question current practices in POCT, and to clinicians seeking evidence-based support for POCT in clinical management. These guidelines represent the most comprehensive systematic review of the POCT literature to date and will help define future research that is needed to add to our current POCT knowledge base.

Predictors of opioid misuse in patients with chronic pain: a prospective cohort study.

BACKGROUND: Opioid misuse can complicate chronic pain management, and the non-medical use of opioids is a growing public health problem. The incidence and risk factors for opioid misuse in patients with chronic pain, however, have not been well characterized. We conducted a prospective cohort study to determine the one-year incidence and predictors of opioid misuse among patients enrolled in a chronic pain disease management program within an academic internal medicine practice. METHODS: One-hundred and ninety-six opioid-treated patients with chronic, non-cancer pain of at least three months duration were monitored for opioid misuse at pre-defined intervals. Opioid misuse was defined as: 1. Negative urine toxicological screen (UTS) for prescribed opioids; 2. UTS positive for opioids or controlled substances not prescribed by our practice; 3. Evidence of procurement of opioids from multiple providers; 4. Diversion of opioids; 5. Prescription forgery; or 6. Stimulants (cocaine or amphetamines) on UTS. RESULTS: The mean patient age was 52 years, 55% were male, and 75% were white. Sixty-two of 196 (32%) patients committed opioid misuse. Detection of cocaine or amphetamines on UTS was the most common form of misuse (40.3% of misusers). In bivariate analysis, misusers were more likely than non-misusers to be younger (48 years vs 54 years, p < 0.001), male (59.6% vs. 38%; p = 0.023), have past alcohol abuse (44% vs 23%; p = 0.004), past cocaine abuse (68% vs 21%; p < 0.001), or have a previous drug or DUI conviction (40% vs 11%; p < 0.001%). In multivariate analyses, age, past cocaine abuse (OR, 4.3), drug or DUI conviction (OR, 2.6), and a past alcohol abuse (OR, 2.6) persisted as predictors of misuse. Race, income, education, depression score, disability score, pain score, and literacy were not associated with misuse. No relationship between pain scores and misuse emerged. CONCLUSION: Opioid misuse occurred frequently in chronic pain patients in a pain management program within an academic primary care practice. Patients with a history of alcohol or cocaine abuse and alcohol or drug related convictions should be carefully evaluated and followed for signs of misuse if opioids are prescribed. Structured monitoring for opioid misuse can potentially ensure the appropriate use of opioids in chronic pain management and mitigate adverse public health effects of diversion.

The use of biochemical markers in osteoporosis.

Osteoporosis is a skeletal disease in which there is a loss of, or de-crease in, bone mass with a deterioration of the microarchitecture of bone tissue. The disease is progressive, taking place over a period of years, and involves derangements in the processes of bone turnover. These derangements can be classified as those in which osteoclast activity (resorption) is stimulated so that more bone is re-moved than formed or in which osteoblast activity (formation) is hindered such that refilling of the resorption cavity is incomplete. Regardless of the process, a key pathologic development is the net loss of bone mass. This article reviews the use of biochemical markers in osteoporosis.