Reference distributions for alpha2-macroglobulin: a practical, simple and clinically relevant approach in a large cohort

The conformational change of the protease inhibitor α2-macroglobulin is triggered by the retraction of the cleaved bait region from a central channel

The protease inhibitor α₂-macroglobulin (A2M) is a member of the ancient α₂-macroglobulin superfamily (A2MF), which also includes structurally related proteins, such as complement factor C3. A2M and other A2MF proteins undergo an extensive conformational change upon cleavage of their bait region by proteases. However, the mechanism whereby cleavage triggers the change has not yet been determined. We have previously shown that A2M remains functional after completely replacing its bait region with glycine and serine residues. Here, we use this tabula rasa bait region to investigate several hypotheses for the triggering mechanism. When tabula rasa bait regions containing disulfide loops were elongated by reducing the disulfides, we found that A2M remained in its native conformation. In addition, cleavage within a disulfide loop did not trigger the conformational change until after the disulfide was reduced, indicating that the introduction of discontinuity into the bait region is essential to the trigger. Previously, A2MF structures have shown that the C-terminal end of the bait region (a.k.a. the N-terminal region of the truncated α chain) threads through a central channel in native A2MF proteins. Bait region cleavage abolishes this plug-in-channel arrangement, as the bait region retracts from the channel and the channel itself collapses. We found that mutagenesis of conserved plug-in-channel residues disrupted the formation of native A2M. These results provide experimental evidence for a structural hypothesis in which retraction of the bait region from this channel following cleavage and the channel’s subsequent collapse triggers the conformational change of A2M and other A2MF proteins.

Activated Alpha-2 Macroglobulin Improves Insulin Response via LRP1 in Lipid-Loaded HL-1 Cardiomyocytes

Activated alpha-2 Macroglobulin (α₂M*) is specifically recognized by the cluster I/II of LRP1 (Low-density lipoprotein Receptor-related Protein-1). LRP1 is a scaffold protein for insulin receptor involved in the insulin-induced glucose transporter type 4 (GLUT4) translocation to plasma membrane and glucose uptake in different types of cells. Moreover, the cluster II of LRP1 plays a critical role in the internalization of atherogenic lipoproteins, such as aggregated Low-density Lipoproteins (aggLDL), promoting intracellular cholesteryl ester (CE) accumulation mainly in arterial intima and myocardium. The aggLDL uptake by LRP1 impairs GLUT4 traffic and the insulin response in cardiomyocytes. However, the link between CE accumulation, insulin action, and cardiac dysfunction are largely unknown. Here, we found that α₂M* increased GLUT4 expression on cell surface by Rab4, Rab8A, and Rab10-mediated recycling through PI₃K/Akt and MAPK/ERK signaling activation. Moreover, α₂M* enhanced the insulin response increasing insulin-induced glucose uptake rate in the myocardium under normal conditions. On the other hand, α₂M* blocked the intracellular CE accumulation, improved the insulin response and reduced cardiac damage in HL-1 cardiomyocytes exposed to aggLDL. In conclusion, α₂M* by its agonist action on LRP1, counteracts the deleterious effects of aggLDL in cardiomyocytes, which may have therapeutic implications in cardiovascular diseases associated with hypercholesterolemia.

Quench me if you can: Alpha-2-macroglobulin trypsin complexes enable serum biomarker analysis by MALDI mass spectrometry

One of the main functions of alpha-2-macroglobulin (A2M) in human blood serum is the binding of all classes of protease. It is known that trypsin, after such interaction, possesses modified proteolytic activity. Trypsin first hydrolyzes two bonds in A2M's 'bait region', and the peptide ⁷⁰⁵VGFYESDVMGR⁷¹⁵ is released from A2M. In this work, specifics of the A2M-trypsin interaction were used to determine A2M concentration directly in human blood serum using MALDI mass-spectrometry. Following exogenous addition of trypsin to human blood serum in vitro, the concentration of the VGFYESDVMGR peptide was measured, using its isotopically-labeled analogue (¹⁸O), and A2M concentration was calculated. The optimized mass spectrometric approach was verified using a standard method for A2M concentration determination (ELISA) and the relevant statistical analysis methods. It was also shown that trypsin's modified proteolytic activity in the presence of serum A2M can be used to analyze other serum proteins, including potential biomarkers of pathological processes. Thus, this work describes a promising approach to serum biomarker analysis that can be technically extended in several useful directions.

Predictive Modeling of Thoracic Radiotherapy Toxicity and the Potential Role of Serum Alpha-2-Macroglobulin

Background: To investigate the impact of alpha-2-macroglobulin (A2M), a suspected intrinsic radioprotectant, on radiation pneumonitis and esophagitis using multifactorial predictive models. Materials and Methods: Baseline A2M levels were obtained for 258 patients prior to thoracic radiotherapy (RT). Dose-volume characteristics were extracted from treatment plans. Spearman's correlation (Rs) test was used to correlate clinical and dosimetric variables with toxicities. Toxicity prediction models were built using least absolute shrinkage and selection operator (LASSO) logistic regression on 1,000 bootstrapped datasets. Results: Grade ≥2 esophagitis and pneumonitis developed in 61 (23.6%) and 36 (14.0%) patients, respectively. The median A2M level was 191 mg/dL (range: 94-511). Never/former/current smoker status was 47 (18.2%)/179 (69.4%)/32 (12.4%). We found a significant negative univariate correlation between baseline A2M levels and esophagitis (Rs = -0.18/p = 0.003) and between A2M and smoking status (Rs = 0.13/p = 0.04). Further significant parameters for grade ≥2 esophagitis included age (Rs = -0.32/p < 0.0001), chemotherapy use (Rs = 0.56/p < 0.0001), dose per fraction (Rs = -0.57/p < 0.0001), total dose (Rs = 0.35/p < 0.0001), and several other dosimetric variables with Rs > 0.5 (p < 0.0001). The only significant non-dosimetric parameter for grade ≥2 pneumonitis was sex (Rs = -0.32/p = 0.037) with higher risk for women. For pneumonitis D15 (lung) (Rs = 0.19/p = 0.006) and D45 (heart) (Rs = 0.16/p = 0.016) had the highest correlation. LASSO models applied on the validation data were statistically significant and resulted in areas under the receiver operating characteristic curve of 0.84 (esophagitis) and 0.78 (pneumonitis). Multivariate predictive models did not require A2M to reach maximum predictive power. Conclusion: This is the first study showing a likely association of higher baseline A2M values with lower risk of radiation esophagitis and with smoking status. However, the baseline A2M level was not a significant risk factor for radiation pneumonitis.

Proteomic analysis of synovial fluid from rheumatic arthritis and spondyloarthritis patients

Background

The aetiologies and pathogeneses of the joint diseases rheumatoid arthritis (RA) and spondyloarthritis (SpA) are still not fully elucidated. To increase our understanding of the molecular pathogenesis, we analysed the protein composition of synovial fluid (SF) from rheumatoid arthritis (RA) and spondyloarthritis (SpA) patients.

Methods

Fifty-six synovial fluid samples (RA, n = 32; SpA, n = 24) were digested with trypsin, and the resulting peptides were separated by liquid chromatography and analysed by tandem mass spectrometry. Additionally, the concentration of cell-free DNA (cfDNA) in the synovial fluid was measured, and plasma C-reactive protein (CRP) was determined.

Results

Three hundred thirty five proteins were identified within the SF. The more abundant proteins seen in RA SF were inflammatory proteins, including proteins originating from neutrophil granulocytes, while SpA SF had less inflammatory proteins and a higher concentration of haptoglobin. The concentration of cell-free DNA in the SF increased together with proteins that may have originated from neutrophils. Plasma CRP levels in both RA and SpA, correlated to other acute phase reactants.

Conclusions

The proteomic results underline that neutrophils are central in the RA pathology but not in SpA, and even though inhibitors of neutrophils (migration, proteinase inhibitors) were present in the SF it was not sufficient to interrupt the disease process.

Identification of Potential Novel Interacting Partners for Coagulation Factor XIII B (FXIII-B) Subunit, a Protein Associated with a Rare Bleeding Disorder

Coagulation factor XIII (FXIII) is a plasma-circulating heterotetrameric pro-transglutaminase complex that is composed of two catalytic FXIII-A and two protective/regulatory FXIII-B subunits. FXIII acts by forming covalent cross-links within a preformed fibrin clots to prevent its premature fibrinolysis. The FXIII-A subunit is known to have pleiotropic roles outside coagulation, but the FXIII-B subunit is a relatively unexplored entity, both structurally as well as functionally. Its discovered roles so far are limited to that of the carrier/regulatory protein of its partner FXIII-A subunit. In the present study, we have explored the co-presence of protein excipients in commercial FXIII plasma concentrate FibrogamminP by combination of protein purification and mass spectrometry-based verification. Complement factor H was one of the co-excipients observed in this analysis. This was followed by performing pull down assays from plasma in order to detect the putative novel interacting partners for the FXIII-B subunit. Complement system proteins, like complement C3 and complement C1q, were amongst the proteins that were pulled down. The only protein that was observed in both experimental set ups was alpha-2-macroglobulin, which might therefore be a putative interacting partner of the FXIII/FXIII-B subunit. Future functional investigations will be needed to understand the physiological significance of this association.

A score derived from routine biochemical parameters increases the diagnostic accuracy of chromogranin A in detecting patients with neuroendocrine neoplasms

BACKGROUND

Chromogranin A (CgA) is a valuable biomarker for detection and follow-up of patients with neuroendocrine neoplasms (NENs). However, various comorbidities may influence serum CgA, which decreases its diagnostic accuracy. We aimed to investigate which laboratory parameters are independently associated with increased CgA in real-life setting and to develop a scoring system, which could improve the diagnostic accuracy of CgA in detecting patients with NENs.

METHODS

This retrospective study included 55 treatment naïve patients with NENs and160 patients with various comorbidities but without NEN (nonNENs). Scoring system (CgA-score) was developed based on z-scores obtained from receiver operating curve analysis for each parameter that was associated with elevated serum CgA in nonNENs.

RESULTS

CgA correlated positively with serum BUN, creatinine, α2-globulin, red-cell distribution width, erythrocyte sedimentation rate, plasma glucose and correlated inversely with hemoglobin, thrombocytes and serum albumin. Serum CgA was also associated with the presence of chronic renal failure, arterial hypertension and diabetes and the use of PPI. In the entire study population, CgA showed an area under the curve of 0.656. Aforementioned parameters were used to develop a CgA-score. In a cohort of patients with CgA-score <12.0 (N = 87), serum CgA >156.5 ng/ml had 77.8% sensitivity and 91.5% specificity for detecting NENs (AUC 0.841, 95% CI 0.713-0.969, P < 0.001). Serum CgA had no diagnostic value in detecting NENs in patients with CgA-score >12.0 (AUC 0.554, 95% CI 0.405-0.702, P = 0.430).

CONCLUSIONS

CgA-score encompasses a wide range of comorbidities and represents a promising tool that could improve diagnostic performance of CgA in everyday clinical practice.

Biochemical Foundations of Health and Energy Conservation in Hibernating Free-ranging Subadult Brown Bear Ursus arctos

Brown bears (Ursus arctos) hibernate for 5-7 months without eating, drinking, urinating, and defecating at a metabolic rate of only 25% of the summer activity rate. Nonetheless, they emerge healthy and alert in spring. We quantified the biochemical adaptations for hibernation by comparing the proteome, metabolome, and hematological features of blood from hibernating and active free-ranging subadult brown bears with a focus on conservation of health and energy. We found that total plasma protein concentration increased during hibernation, even though the concentrations of most individual plasma proteins decreased, as did the white blood cell types. Strikingly, antimicrobial defense proteins increased in concentration. Central functions in hibernation involving the coagulation response and protease inhibition, as well as lipid transport and metabolism, were upheld by increased levels of very few key or broad specificity proteins. The changes in coagulation factor levels matched the changes in activity measurements. A dramatic 45-fold increase in sex hormone-binding globulin levels during hibernation draws, for the first time, attention to its significant but unknown role in maintaining hibernation physiology. We propose that energy for the costly protein synthesis is reduced by three mechanisms as follows: (i) dehydration, which increases protein concentration without de novo synthesis; (ii) reduced protein degradation rates due to a 6 °C reduction in body temperature and decreased protease activity; and (iii) a marked redistribution of energy resources only increasing de novo synthesis of a few key proteins. The comprehensive global data identified novel biochemical strategies for bear adaptations to the extreme condition of hibernation and have implications for our understanding of physiology in general.

The bromocresol green assay, but not the modified bromocresol purple assay, overestimates the serum albumin concentration in nephrotic syndrome through reaction with α2-macroglobulin

Background

The bromocresol green (BCG) assay is commonly used for measuring albumin (ALB), but is affected by α1- and α2-globulins, which are elevated in systemic inflammation. The modified bromocresol purple (mBCP) assay is another dye-binding method developed to overcome non-specific reactions. Concentrations of α2-macroglobulin, a major α2-globulin component, are increased in nephrotic syndrome (NS), but not in inflammation. There is little direct evidence that α2-macroglobulin affects BCG or mBCP assays.

Methods

We measured serum albumin concentrations in 33 patients with NS and 13 reference healthy controls using BCG (ALBBCG) and mBCP (ALBmBCP) assays, and nephelometry (nALB) as a reference method. We also determined five specific proteins belonging to the α1- and α2-globulins by nephelometry. After adding purified α2-macroglobulin to albumin solutions, protein reactivity in these three assays was compared.

Results

Nephrotic syndrome patients were categorized to tertiles according to nALB concentration. In all tertiles, ALBBCG was significantly higher than nALB, especially in the severe hypoalbuminemia group, in which α2-macroglobulin was 43–49% higher. By contrast, ALBmBCP and nALB were almost identical in all three groups. The difference between ALBBCG and nALB was positively correlated with the α2-macroglobulin concentration. In vitro, when α2-macroglobulin was added to solutions containing identical albumin concentrations, α2-macroglobulin dose-dependently increased ALBBCG, but not ALBmBCP.

Conclusions

In NS, α2-macroglobulin is a major factor for positive bias of ALBBCG, especially in patients with severe hypoalbuminemia. The mBCP assay is useful for measuring albumin concentrations in NS.

Protein molecular forms of insulin-like growth factor binding protein-2 change with aging

Aging is considered to be an adaptive mechanism to altered needs of an organism and/or to altered stimuli. Plasma concentrations of insulin-like growth factor binding protein-2 (IGFBP-2) increase with age and it is generally assumed that IGFBP-2 is a negative predictor of healthy aging. The aim of this study was to examine the distribution of IGFBP-2 molecular forms in different age groups and, specifically, the relationship between IGFBP-2 and alpha-2-macroglobulin (α2M). The relative amount of monomer IGFBP-2 was the highest in young persons, making up approximately 2/3 of the total circulating IGFBP-2. This gradually decreased with age down to 1/3 of total IGFBP-2 in elderly individuals. Fragmented IGFBP-2 increased with age and contributed almost 60% to the total immunoreactive IGFBP-2 in the age group 61-80 years. IGFBP-2/α2M complexes represented 10-12% of the total IGFBP-2 in the two younger groups but half this level in the oldest group. The significance of these changes and whether they affect more IGF-dependent or independent interactions are unknown. Due to drastic proteolysis of IGFBP-2, it may be postulated that either over-release of IGFBP-2-bound IGFs causes unwanted events or IGFBP-2 fragments are able to over-stimulate cellular processes.

Acute phase proteins are major clients for the chaperone action of α₂-macroglobulin in human plasma

Extracellular protein misfolding is implicated in many age-related diseases including Alzheimer's disease, macular degeneration and arthritis. In this study, putative endogenous clients for the chaperone activity of α₂-macroglobulin (α₂M) were identified after human plasma was subjected to physiologically relevant sheer stress at 37 °C for 10 days. Western blot analysis showed that four major acute phase proteins: ceruloplasmin, fibrinogen, α₁-acid glycoprotein and complement component 3, preferentially co-purified with α₂M after plasma was stressed. Furthermore, the formation of complexes between α₂M and these putative chaperone clients, detected by sandwich ELISA, was shown to be enhanced in response to stress. These results support the hypothesis that α₂M plays an important role in extracellular proteostasis by sequestering misfolded proteins and targeting them for disposal, particularly during acute phase reactions.

Cardiac isoform of alpha 2 macroglobulin: a marker of cardiac involvement in pediatric HIV and AIDS

Cardiac involvement in children with human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) is known but less often considered. Our objectives were to determine cardiac manifestations in pediatric HIV/AIDS and estimate the cardiac isoform of alpha-2 macroglobulin [CA2M] among them. We recruited 67 pediatric HIV/AIDS patients, 37 with cardiac involvement (group A) and 30 without (group B); 30 cardiac patients without HIV infection (group C); and 30 healthy control subjects without any comorbid illness (group D). Their sociodemographic and clinical information were collected along with echocardiogram and blood for CA2M. Patterns of cardiac involvement in HIV/AIDS (group A) were pericardial effusion, left ventricular dysfunction, pulmonary hypertension, and cardiomyopathy and observed in 43, 30, 16, and 11% of subjects, respectively. CA2M levels among groups A, B, C, and D were 132.67 +/- 5.01, 41.25 +/- 3.33, 65.99 +/- 2.48 and 29.59 +/- 2.76 microgm/ml, respectively. It was elevated significantly in group A (P = 0.001; 95% confidence interval [CI] 87.27-95.55) compared with group B and was independent of sex and CD4 count among HIV/AIDS subjects. Although CA2M was elevated in HIV-negative patients with cardiac involvement, it was much less than in HIV/AIDS subjects with cardiac involvement (P = 0.001; 95% CI 62.54-70.82). Because CA2M is a cardiac biomarker, further research with larger population is needed to ascertain the role of CA2M as a diagnostic/therapeutic/prognostic marker in cardiac patients with and without HIV infection.

FibroTest-ActiTest as a non-invasive marker of liver fibrosis

FibroTest (FT) is a biomarker of liver fibrosis initially validated in patients with chronic hepatitis C (CHC) and subsequently assessed in other frequent liver diseases, including chronic hepatitis B (CHB), alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD). The primary aim of the present study was to update a previous meta-analysis of FT diagnostic value, and to summarize its advantages and limitations. The secondary aim was to provide an overview of the prognostic value of FT in CHC, CHB and ALD. For diagnostic value, the main endpoint was the FT area under the ROC curves (AUROCs) for the diagnosis of bridging fibrosis (F2/F3/F4 vs F0/F1), standardized for the spectrum of fibrosis. Sensitivity analysis integrated the non-standardized observed AUROCs, the independency of authors, size (length) of biopsy, prospective design, correctness of procedures, co-morbidities, and timelag between biopsy and serum sampling. For prognostic value, the main endpoint was the FT AUROC for the prognostic value of liver complications or death related to liver disease. A total of 38 diagnostic studies were included, which pooled 7985 subjects who had undergone both FT and biopsy (4600 HCV, 1580 HBV, 267 NAFLD, 524 ALD and 1014 mixed). The mean standardized AUROC was 0.84 (95% CI, 0.83-0.86), with no differences in terms of causes of liver disease: HCV 0.84 (0.82-0.87); HBV 0.81 (0.78-0.83); NAFLD 0.84 (0.76-0.92); ALD 0.87 (0.82-0.92); and mixed 0.85 (0.81-0.89). Three prognostic studies were also included. FT was found to have higher or similar prognostic value compared with biopsy in patients with CHC, CHB or ALD. FibroTest is an effective alternative to biopsy in patients with chronic hepatitis C or B, ALD or NAFLD. Indeed, the prognostic performance of FibroTest was at least as accurate as that of biopsy in patients with chronic hepatitis C or B, or ALD.

Alpha2-macroglobulin is a potential facilitator of prion protein transformation

Cellular prion protein changes conformation during transformation to an infectious scrapie isoform. One measure of transformation is the development of partial resistance to protease treatment. A fraction of human and bovine plasma was identified containing activity that facilitates transformation of cellular prion protein to a protease resistant isoform in the presence of RNA in the absence of seeded scrapie prion protein. Purification of proteins from this fraction led to the identification of alpha2-macroglobulin as an active component suggesting that it may facilitate conformational changes in prion protein in spontaneous forms of prion disease.

Biological markers of liver fibrosis and activity as non-invasive alternatives to liver biopsy in patients with chronic hepatitis C and associated mixed cryoglobulinemia vasculitis

OBJECTIVE AND METHODS

We assessed the reliability of non-invasive biological scoring indexes (Fibrotest-Actitest [FT-AT], Forns, APRI, age-platelet, platelet, hyaluronic acid) as non-invasive alternatives to liver biopsy (LB) in 138 HCV-infected patients.

RESULTS

Thirty-six of 138 (26%) patients had systemic vasculitis, 27% significant serum inflammation, 47% fibrosis (F2F3F4) on LB. The diagnostic value of FT (F2F3F4 vs. F0F1) was assessed by an AUC of 0.83, without difference regarding to systemic vasculitis or serum inflammation. A discordance between FT-AT and the Metavir scoring indexes, present in 29% of patients, was associated with serum hemolysis and male but not with systemic vasculitis or serum inflammation. The other non-invasive biological tests were not influenced by serum inflammation or systemic vasculitis but were less reliable than FT (P <or= 0.05).

CONCLUSION

The FT-AT is a reliable non-invasive biochemical alternative to LB in HCV-infected patients with systemic vasculitis and is more reliable than other non-invasive biological indexes.

Cardiac isoform of alpha-2 macroglobulin—A new biomarker for myocardial infarcted diabetic patients

Cardiac isoform of alpha-2 macroglobulin [cardiac alpha2M] has been shown to be an early marker in cardiac hypertrophy and left ventricular mass in humans. We, here, for the first time report its presence in myocardial infarcted humans and tried to explore the possibility of using this protein as a novel diagnostic marker for myocardial infarcted diabetic patients. A total of 260 samples were analyzed in this study for the presence of cardiac alpha2M. These include 55 patients of diabetic with post myocardial infarction [PMI], 45 diabetic patients without PMI, 60 patients of PMI alone and 100 controls without any ailments. Levels of cardiac alpha2M present in the sera of diabetic patients with PMI are significantly higher than that of normal human sera and diabetic patients without PMI but not with PMI alone group, suggesting this protein as a marker for PMI itself. However, our results reveal that cardiac alpha2M could be a valuable marker for the diagnosis of myocardial infarcted diabetic patients and differentiating them from diabetic patients without myocardial infarction by sandwich ELISA.

Apheresis for idiopathic sudden hearing loss: Reviewing the evidence

Plasmapheresis has been used for various conditions for a number of years. Recently, its application for idiopathic sudden hearing loss (ISHL) has met with increasing interest. ISHL affects about 10-20 per 100,000 persons per year, impairing not only their hearing but also their ability to interact socially and their quality of life. ISHL is thought to be a sequela of an underlying microvascular disorder caused by a local hyperviscosity syndrome in the cochlear vessels. Plasmapheresis can effectively lower plasma and whole blood viscosity, improve erythrocyte elasticity, and reduce aggregability. Thus, it may be effectively employed in the treatment of ISHL. This article will briefly outline the background against which apheresis procedures are used in the treatment of ISHL and review studies done to date. Furthermore, a broader basis for the use of apheretic applications in the treatment of ISHL will be suggested, correlating age-adjusted ISHL incidence and age-adjusted levels of macromolecular plasma proteins such as fibrinogen. In conclusion, plasmapheresis is a promising new treatment for ISHL but more basic data on ISHL, and on apheresis applications for ISHL, are needed to safely assess treatment outcomes and possible future applications.

Reference distributions for apolipoproteins AI and B and the apolipoprotein B/AI ratios: a practical and clinically relevant approach in a large cohort

The two serum apolipoproteins in the highest concentrations, apolipoprotein (apo) AI and apolipoprotein B, and the apolipoprotein B/AI ratio are measured to assess clinical risk for atherosclerotic heart and peripheral vascular diseases. The study is based on a cohort of over 37,000 Caucasian individuals from northern New England measured in one laboratory by immunonephelometry using standardized reference materials. All samples received for protein analyses were accepted provided adequate identifying information was available. Laboratory and demographic information was entered into a single database for subsequent study. Our results show that for males without evidence of inflammation, values of apo AI change little through life. For females, however, values gradually increase until about 60 years of age then fall somewhat thereafter. Among adults, females have higher apo AI values on average, than males. Apo B values change significantly through life, increasing after the end of the second decade to a peak during the sixth decade, then falling thereafter. In the past, concern has been expressed that apo AI is an acute phase reactant (APR), thus complicating cardiovascular risk assessment. The effects of an APR (C-reactive protein >or=10 mg/L) on apo AI, but not on apo B, are measurable for both sexes, most noticeably beyond the age of 60 years in males and females. When values were expressed as age- and gender-specific multiples of the median (MoMs), the resulting distributions fit a log-Gaussian distribution well over a broad range. The size of the relatively homogenous cohort, by a standardized approach, provides a firm basis for comparison to preexisting reference intervals and for establishing a clinically useful and current reference interval for the three main apolipoprotein values.

Reference distributions for alpha2-macroglobulin: a comparison of a large cohort to the world's literature

The lack of satisfactory methods for quantifying serum levels and a credible reference material has limited bedside use of serum alpha(2)-macroglobulin (alpha2M) measurements. Great strides have been made in the last few years. The remaining barrier to more relevant and cost effective use of serum protein data for diagnosis and prognosis is the availability of reliable reference intervals from birth to old age for both males and females. A total of 40 publications reporting reference intervals have been identified that meet the criteria used in our prior five studies, and these have been analyzed statistically. On average, previous small studies of these individual proteins agree with our life-long reference ranges over their constrained age ranges. This meta-analysis provides support for our reference ranges and places them in the perspective of previous publications.