Reference intervals for alpha 1-microglobulin in urine

A study on the biological reference interval of urinary alpha 1-microglobulin in a group of Chinese people

OBJECTIVE

The aim of this study was to explore the possible influences of age and gender on urinary Alpha 1-Microglobulin (α1-MG) concentrations and establish specific reference values of urinary α1-MG in a group of healthy adults.

METHODS

Two hundred and ninety-nine adults (141 males and 158 females) aged 20-60 were selected and grouped by gender and age. Urinary levels of α1-MG were detected in morning spot-urine samples, and statistical analysis was performed to explore the association between urinary α1-MG and clinical parameters, and the differences between groups were compared. The 95th percentile of distribution was used as the normal upper limit.

RESULTS

The value of urinary α1-MG was sex-dependent (P<0.001), the 95th percentile of urinary α1-MG of males was 26.4 mg/L, whereas females was 8.6 mg/L. Whereas urinary α1-microglobulin-to-creatinine ratio (α1-MG/Cr) was both gender-and age-dependent (both P<0.001), and age 30 may be the cut-off point in this study. The 95th percentile of males and females aged 20-30 was 16.9 mg/g, of males aged 31-60 was 19.8 mg/g, of females aged 31-60 was 28.5 mg/g.

DISCUSSIONS

The relationship between urinary α1-MG concentrations and gender, age is different from previous studies. It is recommended that hospitals and laboratories should develop their own α1-MG reference intervals based on their experimental conditions.

Investigation of apparent non-albuminuric proteinuria in a primary care population

BACKGROUND

There is debate as to whether using the urinary albumin- or protein-to-creatinine ratio (ACR or PCR) should be the primary test for proteinuria. Whilst albuminuria (increased ACR) in the absence of proteinuria (increased PCR) may be expected in some patients, the converse (i.e., proteinuria in the absence of albuminuria) is more unusual and its cause and significance are unclear. We investigated the nature of such apparent non-albuminuric proteinuria in a primary care population of patients.

METHODS

ACR and PCR were measured in 569 urine samples from patients who either had chronic kidney disease or were at increased risk of the condition. Samples with apparent proteinuria (PCR ≥23 mg/mmol/≥200 mg/g) but no albuminuria (ACR <3.4 mg/mmol/<30 mg/g) were classified as 'discrepant' (37% of proteinuric samples, 6% of all samples); 27 of these samples were available for further analyses. The further analyses included electrophoresis, repeat measurement, immunoassays for markers of tubular proteinuria and use of alternative albumin and total protein methods.

RESULTS

Electrophoresis did not identify significant proteinuria in the discrepant samples. The only evidence of tubular proteinuria following measurement of three urinary markers of the condition was a mildly increased α1-microglobulin-to-creatinine ratio in 10 of the 27 discrepant samples analysed, four of which also had a raised β-trace protein-to-creatinine ratio. Use of an alternative urinary total protein method resulted in significantly lower PCRs and 17 of the 27 samples were no longer classified as proteinuric.

CONCLUSIONS

We were unable to confirm the cause of a raised PCR without albuminuria in these patients and suspect that in most cases it is artefactual.

Alpha 1-microglobulin: clinical laboratory aspects and applications

BACKGROUND

Urinary microproteins are becoming increasingly important in clinical diagnostics. They can contribute in the non-invasive early detection of renal abnormalities and the differentiation of various nephrological and urological pathologies. Alpha 1-microglobulin (A1M) is an immunomodulatory protein with a broad spectrum of possible clinical applications and seems a promising marker for evaluation of tubular function.

METHOD

We performed a systematic review of the peer-reviewed literature (until end of November 2003) on A1M with emphasis on clinical diagnostic utility and laboratory aspects.

CONCLUSIONS

A1M is a 27-kDa glycoprotein, present in various body fluids, with unknown exact biological function. The protein acts as a mediator of bacterial adhesion to polymer surfaces and is involved in inhibiting renal lithogenesis. Because A1M is not an acute phase protein, is stable in a broad range of physiological conditions and sensitive immunoassays have been developed, its measurement can be used for clinical purposes. Unfortunately, international standardisation is still lacking. Altered plasma/serum levels are usually due to impaired liver or kidney functions but are also observed in clinical conditions such as HIV and mood disorders. Urinary A1M provides a non-invasive, inexpensive diagnostic alternative for the diagnosis and monitoring of urinary tract disorders (early detection of tubular disorders such as heavy metal intoxications, diabetic nephropathy, urinary outflow disorders and pyelonephritis).

Changes of urinary alpha1-microglobulin in the assessment of prognosis in renal transplant recipients

BACKGROUND

After transplantation, even if the graft starts functioning immediately, there are morphological and functional changes in tubular structures. In addition, acute allograft rejection causes damage in the tubular epithelium, tubular basement membrane, and intertubular connective tissue. It also affects the functional capacity of proximal tubular cells resulting in impaired reabsorption and thus increased urinary excretion of low molecular weight proteins.

METHODS

We present a double-antibody radioimmunoassay for determination of the concentration of alpha1-microglobulin (alpha1 M) in urine. It was used to measure urinary excretion of alpha1 M approximately once a week during the first 1-6 posttransplant weeks in 136 consecutive patients: 30 patients developing acute rejection (75 24-hr urine samples) and 106 patients with stable graft function (223 24-hr urine samples). The results are expressed as alpha1 M/creatinine ratios.

RESULTS

Approximately 8 days after transplantation the mean (+/-SD) urinary alpha1 M/creatinine ratio of all patients was 17.0+/-14.8 mg/mmol, being about the same both in patients with uncomplicated posttransplantation course (16.3+/-14.0 mg/mmol) and in those who later developed rejection (19.3+/-15.1 mg/mmol), but about 60-fold higher than in healthy controls (0.27+/-0.15 mg/mmol). At that time, when all patients were included there was a correlation (r=0.3465, P<0.001) between alpha1 M/creatinine ratio and duration of cold ischemia. Thereafter, during the second week alpha1 M/creatinine ratio decreased in 89% of patients with stable graft function, but only in 14% of patients who later developed rejection (P<0.001). On the contrary, a significant increase (P<0.01) of alpha1 M/creatinine ratio was observed 4 to 1 day before rejection in all 15 patients, who had urines collected at that time. At the end of the follow-up period, alpha1 M/creatinine ratio in patients with rejection was 3-fold compared with the nonrejecting patients, and 100-fold compared with the healthy controls.

CONCLUSION

These results show that cadaveric transplantation results in impaired low molecular weight protein reabsorption, the degree of dysfunction relating to the duration of cold ischemia, and suggest that during the posttransplant weeks decreasing alpha1 M/creatinine ratio in consecutively collected urine samples indicates improved tubular function and in most cases rules out development of acute rejection.

Diagnostic value of urinary alanine aminopeptidase and N-acetyl-beta-D-glucosaminidase in comparison to alpha 1-microglobulin as a marker in evaluating tubular dysfunction in glomerulonephritis patients

To estimate the diagnostic value of tubular parameters, the urinary alanine aminopeptidase (AAP), N-acetyl-beta-D-glucosaminidase (NAG) and the alpha(1)-microglobulin (a1M) of 150 patients with histologically proven glomerulonephritis (GN) were determined. In addition, the reabsorption rate of the proximal tubule and the fractional excretion of sodium, the free water clearance and the renal function were assessed by inulin and p-aminohippurate (PAH) clearance. Compared to healthy controls, urinary AAP, NAG and a1M were found significantly elevated in GN patients. Morphological tubular changes were confirmed by significant differences in urinary laboratory parameters. In patients with tubular atrophy, the diagnostic sensitivity and specificity were calculated as follows: AAP (0.94/0.35), NAG (0.75/0.59) and a1M (0.73/0.52). In patients showing tubular protein droplets, the values were 0.90/0.17 for AAP, 0.78/0.76 for NAG and 0.84/0.74 for a1M and in patients with interstitial fibrosis, the values were AAP (0.95/0.35), NAG (0.75/0. 46) and a1M (68/0.38). Urinary AAP, NAG and a1M reflect histologically proven tubulus alteration in GN, although in most cases, the renal function is still intact. AAP indicates very early tubular impairment and, in some cases, AAP is elevated although NAG and a1M are still within normal ranges. We suggest that the enzyme activities are useful in the diagnostics of early stages of the disease.

alpha-1-Microglobulin: epidemiological indicator for tubular dysfunction induced by cadmium?

OBJECTIVES

To evaluate the suitability of alpha-1-microglobulin as a marker for cadmium induced renal dysfunction.

METHODS

alpha-1-Microglobulin was studied in a cross sectional survey in relation to the body burden of cadmium. Concentrations of alpha-1-microglobulin in 24 h urine of 831 people aged 2-87 years were analysed in association with urinary cadmium excretion, cadmium blood concentration, age, sex, occupational and smoking history, and estimated creatinine clearance. Participants came from a population residentially exposed to cadmium and from two control populations matched for socioeconomic status.

RESULTS

The excretion of alpha-1-microglobulin/24 h ranged from 0.1 mg to 176.3 mg and 44.4% of samples showed concentrations near the detection limit. Ordinal logistic regression analysis of people of all ages identified a high risk only for males compared with females (odds ratio (OR) 2.14; 95% confidence interval (95% CI) 1.56 to 2.94), age group, and duration of living on contaminated soil (OR 1.03/year; 95% CI 1.02 to 1.04), but not urinary cadmium excretion (OR 1.30; 95% CI 0.96 to 1.77) as significant predictors. For people < or = 50 years of age a weaker effect of sex (OR 1.76; 95% CI 1.13 to 2.73) and age group and an effect of similar magnitude for the duration of soil exposure (OR 1.03; 95% CI 1.01 to 1.04) were found. Also, the urinary cadmium excretion (OR 2.26; 95% CI 1.38 to 3.70) and occupational exposure (OR 1.71; 95% CI 1.03 to 2.83) were found to be significant in this younger age group. The estimated creatinine clearance had no significant impact on the alpha-1-microglobulin excretion.

CONCLUSION

alpha-1-Microglobulin is a suitable marker for early tubular changes only for people < or = 50 years. It may not be sufficiently specific for cadmium, and therefore not a suitable surrogate for cadmium exposure in epidemiological studies.

Analysis of proteinuria: reference limits for urine excretion of albumin, protein HC, immunoglobulin G, kappa- and lambda-immunoreactivity, orosomucoid and alpha 1-antitrypsin

Efficient use of assessment of urine protein excretion in nephrological practice requires adequate reference intervals. To determine the upper reference limits of urine albumin, protein HC (alpha 1-microglobulin, immunoglobulin G (IgG), orosomucoid (alpha 1-acid glycoprotein, alpha 1-antitrypsin, and kappa- and lambda-chain immunoreactivities, the concentrations of these proteins were measured in urine samples from 95 healthy, adult individuals, using rapid, generally available methods and with conditions for urine collection which secured stable protein levels. The obtained values were expressed in mg 1(-1), as the urine protein-creatinine index and as fractional protein-creatinine clearance. No differences were found between the upper reference limits in the first voided morning urine samples and the randomly collected urine samples, nor between the upper reference limits in urine samples collected from males and females. The urinary excretion of the tested proteins did not correlate to age, positive dipsticks for haematuria nor to granular casts in urine sediment. Thus, the same upper reference limits can be used for both sexes and regardless of the type of urine collection. The upper reference limits of urine protein-creatinine index found in this study were: for albumin, 3.8 mg mmol(-1); for protein HC, 0.7 mg mmol; for IgG, 0.8 mg mmol(-1); for orosomucoid, 0.7 mg mmol(-1); for alpha 1-antitrypsin, 0.2 mg mmol(-1), and for kappa-immunoreactivity 0.7 mg mmol(-1). The upper reference limit for lambda-immunoreactivity was below the detection limit.

Rapid screening of low molecular mass proteinuria: evaluation of the first immunochemical test strip for the detection of alpha 1-microglobulin in urine

A new semiquantitative immunochemical test strip for urinary alpha 1-microglobulin, a marker protein for tubular proteinuria, was assessed. This test strip has four colour zones, reflecting alpha 1-microglobulin concentrations of ca. 10, 25, 50, and 80 mg/l. alpha 1-Microglobulin concentrations were measured by means of the test strip and an immunonephelometric method in 330 samples collected as the second voided morning urine. The reading time of the test strip must be strictly observed. Reading one minute earlier or later than the 5 min stated in the instructions led to misclassification of over 70% of the results. Correlation between both methods was highly significant, with a Spearman rank correlation coefficient of rs = 0.84 (P < 0.001). There was a partial overlap of the test strip results in different concentration ranges. An elevation of alpha 1-microglobulin was defined as > 25 mg/l, calculated as the upper limit of the central 95% interval of alpha 1-microglobulin concentration in urine samples measured in a previous study of 304 healthy adults. Using this definition of alpha 1-microglobulin elevation, a sensitivity of 97.5%, specificity of 73.6%, a false-positive rate of 16.6%, and a false-negative rate of 0.9% of the test strip results were obtained. A fraction of 82.4% of the 330 samples investigated was correctly classified as having increased alpha 1-microglobulin concentration or not. Methodical improvements of the test strip are necessary to reduce overlapping results, in order to make the test suitable for screening purposes.