Is osmol gap an effective screen in accurate prediction of toxic volatiles?

A review of the literature was done to determine the number of studies published on the osmol gap. We wanted to examine whether these studies were able to establish a consensus on the formula to be used, the appropriate reference interval to be used and finally the performance of the osmol gap in its ability as a screening test for toxic volatile substance. Our study was disappointing since no published literature exists to allow the clinical laboratory to use the osmol gap based on evidenced based studies.

Ionized calcium: whole blood, plasma or serum?

OBJECTIVES: To determine an optimal specimen type to be used for measurements of ionized calcium (iCa) so that it applies properly to the reference interval. Also to determine the validity of the pH correction that is applied to iCa measurements. METHODS: A reference interval study of normal volunteers was performed using four sample types namely balanced heparin (BH) whole blood, lithium heparin (LH) whole blood, plasma and serum. The sample was treated in an anaerobic fashion and analyzed at 0 and 40 minutes after venipuncture. The effect of pH correction as well as analysis time after collection was also studied. RESULTS: The mean iCa was the highest in BH-treated whole blood when measured immediately. However, it was slightly lower at 40 min after collection (p < 0.001). In contrast, there did not appear to be a significant difference in results when LH-treated whole blood was analyzed at 0 or 40 min. The reference interval for serum was similar to that of whole blood. The reference interval for plasma was dramatically lower than whole blood and plasma. The reference intervals for pH adjusted ionized calcium (iCa-adj) were dramatically lower than those from all specimens without adjustment. The reason for this was that the reference interval for pH in this study had a strong alkaline bias on one instrument and a strong acidic bias on the other. CONCLUSIONS: The sample of choice for ionized calcium analysis appears to be whole blood with either BH or LH. For the LH specimen, there is no significant change over 40 min whereas there is significant change for the BH specimens (-0.030 mmol/L, p < 0.0001). iCa-adj should not be used unless (i) very strict attention is paid to standardization of both the calcium and the pH and (ii) there is a very good reason to believe that the patients' pH is normal at 7.4.

Release of cardiac biochemical and inflammatory markers in patients on cardiopulmonary bypass undergoing coronary artery bypass grafting.

BACKGROUND: Determination of cardiac markers can assess cardiac injury induced by cardiopulmonary bypass (CPB) during coronary artery bypass grafting (CABG). However, the markers and their release pattern are not well defined. This study was aimed at assessing the release and timing of cardiac biochemical and inflammatory markers in patients undergoing elective CABG with CPB. METHODS: Forty patients undergoing elective CABG were included in this study. Blood samples were collected for biochemical measurements at the following time points: immediately prior to the induction of anesthesia, one, six, 12, and 24 hours after initiation of CPB. RESULTS: Increased release of cardiac troponin I was observed one hour after initiation of CPB (p < 0.05) and reached the maximum at 12 hours after CPB (p < 0.01). Serum CK-MB enzyme activity and CK-MB mass both were highly elevated starting at one hour after initiation of CPB, peaked at six hours, and remained elevated until 24 hours after CPB. Both lactate and lactate dehydrogenase were highly elevated six hours after CPB and peaked at 12 hours after CPB (p < 0.01). Serum levels of interleukin-6 and tumor necrosis factor-alpha increased significantly one hour after initiation of CPB and peaked at six hours (p < 0.01), while serum high sensitivity C-reactive protein levels started to elevate 12 hours after CPB (p < 0.01). CONCLUSION: Monitoring of these markers could help to determine implementation of protective interventions during CABG with CPB to prevent myocardial deterioration and to predict the risk and prognosis.

Biochemistry testing associated with pregnancy and the newborn period -- a lot has changed since you were a baby!

Everyone has been a newborn, and everyone's mother has been pregnant. Despite the commonality of these events, medical care and the clinical chemistry laboratory's role in it have changed remarkably over the last 50 years. This review is a historical overview of clinical chemistry testing that is related to pregnancy and the newborn period.

Troponin I testing in dialysis patients presenting to the emergency room: does troponin I predict the 30-day outcome?

BACKGROUND: Troponins are often measured in acutely ill chronic dialysis patients admitted to the emergency room, irrespective of their clinical presentation. The significance of an elevated troponin level in this setting is unclear. METHODS: We identified all chronic dialysis patients presenting over 1 year to a tertiary care hospital emergency room who also had at least one cardiac troponin I (cTnI) level determination. We evaluated presenting complaints, risk factors for cardiac disease, cTnI levels, and major cardiac events (MCE; occurrence of cardiovascular death, myocardial infarction, de novo heart failure, or coronary revascularization) within 30 days by chart review in 149 patients (79 on hemodialysis, 70 on peritoneal dialysis). RESULTS: Chest pain was documented in only 29% of the patients. Twenty-two patients (15%) experienced an MCE. The incidence of an MCE was the same in patients with and without chest pain. A cTnI level >0.1 ng/l was a significant predictor of an MCE (odds ratio 15.2, 95% confidence interval CI 5.26, 43.6). The likelihood ratios for MCEs were 0.32 (CI 0.16, 0.63) for a cTnI level <0.1 ng/l, 0.72 (CI 0.09, 5.5) for cTnI concentrations 0.1-0.3 ng/l, 7.8 (CI 4.2, 15) for a cTnI level >0.3, and 11.7 (CI 4.4, 31) for a cTnI concentration >2.0 ng/l. CONCLUSION: In acutely ill chronic dialysis patients presenting to a hospital emergency room, an elevated cTnI level indicates an increased 30-day cardiac risk, regardless of their clinical presentation.

Osteocalcin and vitamin D status are inversely associated with homeostatic model assessment of insulin resistance in Canadian Aboriginal and white women: the First Nations Bone Health Study.

OBJECTIVE: Osteocalcin, a protein synthesized by osteoblasts, and vitamin D status have independently been implicated in energy metabolism and glucose regulation. This study was conducted to simultaneously explore the relationships among osteocalcin, vitamin D status and indicators of glucose metabolism and adiposity in a mixed-ethnicity cohort of adult women. DESIGN: Cross-sectional. METHODS: Aboriginal and white women (n=368) over 25 years of age (45.3±13.6 years) were studied for measures of osteocalcin and 25-hydroxy vitamin D [25(OH)D] plus glucose metabolism including glucose, insulin, C-peptide, hemoglobin A1c (HbA1c) and homeostatic model assessment of insulin resistance (HOMA-IR). Measures of adiposity included body mass index (BMI) plus total body fat and trunk fat from dual-energy X-ray absorptiometry. RESULTS: Aboriginal women had higher BMI, fat and markers of dysglycemia. Osteocalcin was not different between groups, but 25(OH)D was lower in Aboriginal women. Osteocalcin was inversely related to all five parameters of glucose metabolism, whereas 25(OH)D was inversely related to insulin, C-peptide and HOMA-IR. After accounting for age, ethnicity or adiposity using regression analyses, glucose, HbA1c and HOMA-IR were inversely related to both osteocalcin and 25(OH)D. However, only 25(OH)D was inversely related to C-peptide, and neither osteocalcin nor 25(OH)D was related to insulin. CONCLUSIONS: These data from a unique mixed Aboriginal and white population suggest that both vitamin D and osteocalcin are involved in glucose control.

Vitamin D levels and relative insufficiency in Saskatchewan.

OBJECTIVE: To determine the extent of vitamin D3 deficiency and levels in pregnant First Nations and non-First Nations women in SK. Also, to determine the distribution of vitamin D3 values in the general population in SK. METHODS: Vitamin D3 levels were measured by LC-MS/MS from 19,181 consecutive patient blood/serum samples received at the Saskatchewan Disease Control Laboratory, and from 743 First Nations, and 301 non-First Nations pregnant women in SK. RESULTS: The ages of the 19,181 patient samples ranged from day 1 (0 years) to 102 years. Of the total, 14,658 were female, and 4523 were males. 30.8% had relative vitamin D3 insufficiency (50-75 nmol/L), and 22.5% were in the deficient range (<50 nmol/L). In summer, a larger percentage of SK patients are in the optimum range, whereas in winter, the number of patients in the vitamin D3 deficiency range increased to 33.0% from 14.1%. Samples from pregnant women were collected during the first trimester of pregnancy. Whereas non-First Nations pregnant women had similar vitamin D3 levels to non-pregnant women in SK, vitamin D3 levels were significantly lower than the optimum of 75 nmol/L in pregnant First Nations women than in non-First Nations women. 29.7% of First Nations pregnant women were in the relative insufficiency range, and 45.6% were vitamin D3 deficient. CONCLUSIONS: First Nations pregnant women have lower vitamin D3 levels than non-First Nations pregnant women. This puts them and their unborn babies at high risk of a diverse range of disorders associated with vitamin D3 deficiency or insufficiency.

Reverse pseudohyperkalemia in heparin plasma samples from a patient with chronic lymphocytic leukemia.

OBJECTIVES: To investigate the spurious high potassium results in heparin plasma. DESIGN AND METHODS: Potassium values from heparin plasma, serum, and whole blood in a patient with chronic lymphocytic leukemia were determined and compared on chemistry and blood gas analyzers. RESULTS: Potassium levels were strikingly elevated in heparin plasma compared to serum or whole blood in which the potassium levels were surprisingly normal. CONCLUSIONS: The phenomenon of reverse pseudohyperkalemia should be publicized.

Increased plasma methylglyoxal level, inflammation, and vascular endothelial dysfunction in diabetic nephropathy.

OBJECTIVES: To investigate the association of plasma levels of methylglyoxal (MG) and markers of inflammation/endothelial dysfunction with diabetic nephropathy (DN). DESIGN AND METHODS: Plasma levels of MG, cytokines, and adhesion molecules were measured in type 2 diabetic patients (T2DM), T2DM patients with DN, and the controls. RESULTS: Plasma MG levels in DN were significantly higher than those in T2DM and the controls (312 ± 135 vs. 212 ± 73 and 312 ± 135 vs. 147 ± 78 nmol/L, respectively, P<0.001). The plasma levels of MG were positively correlated with the fasting glucose, HbA1c, and urinary albumin/creatinine ratio (r=0.754, P<0.05). Plasma levels of IL-6, TNF-α, and adhesion molecules were markedly increased in DN compared to T2DM patients and the controls. CONCLUSIONS: Increased plasma levels of MG, cytokines, and adhesion molecules are associated with DN. These markers may be useful in predicting the development of DN.

Closing the anion gap: contribution of D-lactate to diabetic ketoacidosis.

BACKGROUND: A high anion gap in diabetic ketoacidosis (DKA) suggests that some unmeasured anions must contribute to the generation of the anion gap. We investigated the contribution of D-lactate to the anion gap in DKA. METHODS: Diabetic patients with and without DKA and high anion gap were recruited. Plasma D-lactate was quantified by HPLC. Plasma methylglyoxal was assayed by liquid chromatography-tandem mass spectrometry. RESULTS: The plasma fasting glucose, ß-hydroxybutyrate, and blood HbA1c levels were highly elevated in DKA. Plasma anion gap was significantly increased in DKA (20.59±6.37) compared to either the diabetic (7.50±1.88) or the control group (6.53±1.75) (p<0.001, respectively). Moreover, plasma D-lactate levels were markedly increased in DKA (3.82±2.50 mmol/l) compared to the diabetic (0.47±0.55 mmol/l) or the control group (0.25±0.35 mmol/l) (p<0.001, respectively). Regression analysis demonstrated that D-lactate was associated with acidosis and anion gap (r=0.686, p<0.001). CONCLUSIONS: Plasma D-lactate levels are highly elevated and associated with metabolic acidosis and the high anion gap in DKA. Laboratory monitoring of d-lactate will provide valuable information for assessment of patients with DKA.

Elevated lactate in ethylene glycol poisoning: True or false?

BACKGROUND: There have been an increasing number of reports on false increase of lactate in ethylene glycol poisoning. We recently encountered two cases of ethylene glycol poisoning with very high blood lactate concentrations on ABL blood gas analyzers. METHODS: Patient plasma lactate concentrations were measured on different chemistry instruments in addition to ABL analyzer. Serum ethylene glycol and glycolic acid were also determined. Lactate values were determined from samples spiked with various amounts of glycolic acid. RESULTS: In case 1, all the chemistry instruments produced similar lactate results compared to that by ABL analyzer whereas in case 2, the lactate on the ABL was dramatically elevated compared to that from all the chemistry analyzers. There was no glycolic acid detected in case 1 but high glycolic acid was obtained in case 2. Increased concentrations of glycolic acid resulted in a significant positive interference on lactate measurements on the ABL analyzer but none on other instruments. CONCLUSIONS: False increase of blood lactate by blood gas analyzers may occur but true increase of lactate can also be observed in ethylene glycol poisoning. Elevated lactate concentrations on blood gas analyzers should be confirmed by a chemistry analyzer in the differential diagnosis of ethylene glycol poisoning.

Thyroglobulin and anti-thyroglobulin assays in thyroid cancer monitoring.

OBJECTIVES: To compare four methods for thyroglobulin (Tg) quantitation and three methods for detection and quantitation of thyroglobulin antibodies (Tg-Ab). We also wanted to explore the premise that thyroglobulin antibodies, as determined by commercially available assays, interfere with thyroglobulin assays in a predictable way. METHODS: Split sample method comparisons were run on all the methods for both the thyroglobulin and anti-thyroglobulin assays. In addition to this, samples from patients that had disseminated thyroid cancer but had low serum thyroglobulin concentrations and high thyroglobulin antibodies were further studied. These studies involved doing recovery studies (or antibody inhibition studies). RESULTS: There was good agreement between methods for quantitation of thyroglobulin with slopes ranging from 0.77 to 1.23 although closer agreement was expected as the assays are all calibrated to the same reference standard (CRM 457). The situation for the thyroglobulin antibody assays is significantly worse, and the rate of antibody positivity ranged from 9-21% in this group of patients although there was agreement in only 6%. Different reference standards are used for the Tg-Ab assays we investigated. The Tg-Ab data did not lend itself to traditional linear regression analysis as the data showed wide scatter. CONCLUSIONS: There is good agreement between the four thyroglobulin assays compared in this study. The linear regression analysis shows that there is proportional error present between the methods that is greater than 50%. This study is unable to demonstrate any difference in assay values based on the amount of anti-thyroglobulin present in the specimen. The agreement between different anti-thyroglobulin assays is very poor. This finding is very problematic since it makes it difficult to generalize any literature reports of interference. All the thyroglobulin assays appear to be suitable for monitoring patients with thyroid cancer, provided that the differences in calibration are taken into account. Differences in calibration between different assays need to be taken into account when changing assays. Conversely, the anti-thyroglobulin assays are virtually useless since there appears to be very little agreement between the three assays studied and no evidence of assay interference in the measurements of thyroglobulin.

Heat-insoluble cryoglobulin in a patient with essential type II cryoglobulinemia and cryoglobulin-occlusive membranoproliferative glomerulonephritis: case report and literature review.

BACKGROUND: A type of heat-insoluble cryoglobulin has been rarely reported and poorly understood. We report the case of a 79 y-old female who was admitted to hospital due to edema and renal failure. METHODS: Serial biochemical, immunological, and histological investigations were conducted. RESULTS: This patient had elevated serum urea and creatinine with positive rheumatoid factor and low serum C3 and C4. Her serum was positive for cryoglobulin at 4 degrees C. The precipitate did not dissolve at 37 degrees C until it was heated to 56 degrees C. Electrophoresis of the cryoglobulin demonstrated a monoclonal spike in the gamma region characterized as IgG-kappa and polyclonal IgM by immunofixation. Bone marrow aspiration showed presence of 5% plasma cells. Histological examination of renal biopsy revealed a diffuse increase in mesangial matrix, cellularity and endocapillary proliferation. Numerous monocyte/macrophages were present within mesangium and capillary lumina. Focal double contouring of glomerular basement membrane with subendothelial deposits and "hyaline thrombi" were noted. Accordingly, a type II heat-insoluble cryoglobulinemia associated with membranoproliferative glomerulonephritis and monoclonal gammopathy of undetermined significance was made. CONCLUSIONS: The unusual heat-insoluble cryoglobulins may indicate severe clinical consequence. Proper laboratory procedure and careful examination of cryoglobulin will assure early recognition and detection of heat-insoluble cryoglobulins.

Bone turnover markers in the management of postmenopausal osteoporosis.

Osteoporosis is the most common cause of fragility fractures. Bone remodelling is essential for repairing damaged areas within bone to preserve bone strength and for assisting in mineral homeostases. In young adults, bone remodelling is usually balanced with approximately as much bone replaced as is removed during each remodelling cycle. However, when remodelling becomes accelerated in combination with an imbalance that favours bone resorption over formation, such as during menopause, precipitous losses in bone mass occur. Bone turnover markers (BTMs) measure the rate of bone remodelling allowing for a dynamic assessment of skeletal status and hold promise in identifying those at highest risk of rapid bone loss and subsequent fracture. Further, the use of BTMs to monitor individuals administered osteoporosis therapy is attractive as monitoring anti-fracture efficacy with bone mineral density has significant limitations. This review details remodelling biology, pre-analytical and analytical sources of variability for BTMs, describes the most commonly used resorption and formation markers, and offers some guidelines for their use and interpretation in the laboratory and the clinic.

Lithium heparinised blood-collection tubes give falsely low albumin results with an automated bromcresol green method in haemodialysis patients.

BACKGROUND: The aim of this study was to investigate the cause of markedly low albumin values determined by a bromcresol green (BCG) method in patients on haemodialysis. METHODS: Serum and heparinised plasma from haemodialysis patients and normal controls were collected. Albumin was measured using Beckman bromcresol purple (BCP) and Roche BCG methods on the Beckman Synchron LX20. RESULTS: The albumin in heparinised plasma determined by a BCG method was 33.3% lower than that of the BCP method in a haemodialysis patient. The albumin values determined by the BCP method were comparable to those measured by immunonephelometric analysis for this patient. Significantly lower albumin levels were also observed in lithium heparin plasma by a BCG method compared to the BCP method in both non-renal patients (31.2+/-3.8 vs. 34.1+/-4.1 g/L, p<0.001, n=30) and haemodialysis patients (28.6+/-3.5 vs. 32.8+/-3.7 g/L, p<0.001, n=30). This negative bias was directly correlated with heparin concentrations in the plasma. The BCP method did not show this dose-dependent bias. CONCLUSIONS: Lithium heparin plasma can cause falsely low albumin values by an automated BCG method and the suitability of lithium heparin blood tubes should be carefully assessed for haemodialysis patients. The BCP method is free of this bias.

Canadian Aboriginal women have a higher prevalence of vitamin D deficiency than non-Aboriginal women despite similar dietary vitamin D intakes.

Canadian Aboriginal women have high rates of bone fractures, which is possibly due to low dietary intake of minerals or vitamin D. This study was undertaken to estimate dietary intake of calcium and vitamin D by designing a culturally appropriate dietary survey instrument and to determine whether disparities exist between Aboriginal and white women. After validation of a FFQ, 183 urban-dwelling and 26 rural-dwelling Aboriginal women and 146 urban white women completed the validated FFQ and had serum 25-hydroxyvitamin D [25(OH)D] measured. Urban Aboriginal women had lower (P=0.0004) intakes of total dietary calcium than urban white women; there was no difference in rural Aboriginal women. Only a minority of all women met the adequate intake (AI) for calcium intake. Ethnicity did not affect total vitamin D intake; however, rural Aboriginal women consumed all of their dietary vitamin D from food sources, which was more (P<0.03) than both urban Aboriginal and white women. Rural and urban Aboriginal women had lower (P<0.0004) serum 25(OH)D than urban white women. We found that 32% of rural Aboriginal, 30.4% of urban Aboriginal, and 18.6% of urban white women were vitamin D deficient, with serum 25(OH)D concentrations<37.5 nmol/L. The high prevalence of vitamin D deficiency among Aboriginal women, combined with lower dietary intake of calcium, especially in older women, likely contributes to the higher incidence of fracture in this population.

Osmolality gaps: diagnostic accuracy and long-term variability.

BACKGROUND: The osmolal gap (OG) is a screening test for the detection of toxic volatiles such as methanol and ethylene glycol. We used mean values of patient data to assess the diagnostic accuracy and long-term stability of OG measurements. METHODS: In a prospective study period in 2003, all requests for volatiles had OGs calculated and quality-control samples were analyzed for OG. ROC curves were constructed to determine whether OG could predict the presence of toxic volatiles in serum. This was also done in a retrospective study for data from 1996 to 2004. Our laboratory database was searched for all emergency room patients for the period of 1996 to 2004 who had tests ordered that allowed us to calculate OGs. RESULTS: For the prospective study period in 2003, the ROC areas indicated that we could accurately predict the presence of toxic volatiles but at markedly different decision cutpoints depending on the formula used. These cutpoints ranged from +10 to +33 mosmol/kg. In the retrospective study, the mean OGs in the patient population for each of the 3 formulas increased by 12 mosmol/kg from 1996 to 2004. For this reason, the diagnostic accuracy was poor when all data were analyzed together. CONCLUSIONS: Under properly controlled conditions, the OG has high sensitivity and specificity for detection of poisoning with some volatiles. Over the long term, however, use of the reference interval of -10 to +10 mosmol/kg yields poor diagnostic accuracy because mean OGs are not constant over time. Bedside calculation is not advisable.

A simple method for quantifying fentanyl, sufentanil, or morphine in discard syringes from anesthesia procedures.

Fentanyl, sufentanil, and morphine are commonly used in the conduct of anesthesia. Medical staff working with these drugs are at high risk of addiction. To detect and prevent diversion, a method was developed to quantify these drugs in discard syringes using the BioRad REMEDi HS Drug Profiling System. For fentanyl, the lowest concentration detected is 0.1 microg/mL, and the assay is linear to 5.0 microg/mL; the within-run coefficient of variation (CV) is 0.9% (n = 5), and between-run CV is 2.5% (n = 20). For sufentanil, the lowest concentration detected is 0.5 microg/mL, and the assay is linear to 11.0 microg/mL; the within-run CV is 2.0% (n = 5), and the between-run CV is 2.4% (n = 20). For morphine, the lowest concentration detected is 0.5 microg/mL, and the assay is linear to 10.0 microg/mL; the within-run CV is 11.6% (n = 5), and between-run CV is 11.3% (n = 20). Other drugs commonly used in the operating room were checked for cross-reactivity on the REMEDi HS; none cross-reacted. The REMEDi HS can be used for rapid, accurate quantification of fentanyl, sufentanil, and morphine in discard syringes from anesthesia procedures or related medical applications.