Serum α₁-Antitrypsin But Not Complement C3 and C4 Predicts Chronic Inflammation in Hemodialysis Patients

Abstract

Background. We studied whether predialysis serum levels of positive acute phase markers such as α₁-antitrypsin (AT), and complement components C3 and C4 could identify the presence of chronic inflammation in maintenance hemodialysis (HD) patients. Methods/Results. In 103 stable HD patients, AT directly correlated with C-reactive protein (CRP) (P<0.005), α₁ acid-glycoprotein (P<0.005), fibrinogen (P<0.05), lipoprotein (a) (P<0.01) and von Willebrand factor antigen (P<0.05), while C3 and C4 were not related to any of these inflammatory markers. In the patients with elevated CRP and hypoalbuminemia, the mean AT value of 1.74 ± 0.50 g/L was higher (P = 0.008) than that of 1.38 ± 0.27 g/L in the subjects with normal CRP and albumin. Using the above cut-off levels, the positive and negative predictive values of AT on the presence of severe inflammation were 0.86 and 0.62, respectively, and the sensitivity and specificity were 86% and 73%, respectively. Conclusion. Serum AT levels above 1.74 g/L and below 1.38 g/L may select the HD patients with severe inflammation from those without. Measurements of C3 and C4 are not helpful in this situation.

• α₁-Antitrypsin
• C3 and C4 of complement
• Hemodialysis
• Inflammation

Introduction

Chronic inflammation contributes to the development of malnutrition, atherosclerosis and cardiovascular disease in maintenance hemodialysis (HD) patients.[[1]], [[2]] Prevalence of this deleterious condition has been found to be well-reflected by increased blood levels of hepatic acute-phase reactants such as C-reactive protein (CRP),[[3]], [[4]], [[5]] fibrinogen,[[3]], [[6]], [[7]], [[8]] lipoprotein (a),[[3]], [[9]] α₁ acid-glycoprotein (also known as orosomucoid),[[5]], [[10]] and vascular endothelium-derived von Willebrand factor antigen (vWF:Ag),[[7]], [[11]] as well as by low albumin concentrations.[[3]], [[4]], [[5]], [[7]]

We compared predialysis serum levels of positive acute-phase reactants such as α₁-antitrypsin (AT, also known as α₁-proteinase inhibitor) and complement components C3 and C4[[12]], [[13]] with those of the established inflammatory markers in maintenance HD patients. We aimed to determine whether serum AT, C3 or C4 levels could identify the presence of a chronic inflammatory state in this population.

Patients and Methods

One hundred and three (39 females) clinically stable patients aged 57 (range: 16–78) years, receiving standard three times a week HD for 17 (1–110) months were enrolled in the study. None of them suffered from any infectious or acute inflammatory diseases during the month preceding the study onset. Fasting blood was obtained from the arterial outlet of the native fistula before onset of a midweek dialysis.

Serum AT, complement C3 and C4, α₁ acid-glycoprotein and CRP levels were measured by nephelometry (Orion Diagnostica, Espoo, Finland). The detection limit of the latex-enhanced CRP assay was 6 mg/L, and for statistical analysis all values <6 mg/L were treated as 5 mg/L. Plasma fibrinogen was determined by the one-stage clotting method, and serum albumin by the bromocresol green dye method. Immunoenzymatic assays were used to measure plasma levels of lipoprotein (a) (Biopool, Umeå, Sweden) and vWF:Ag (Diagnostica Stago, Asnieres-sur-Seine, France).

Data were presented as mean ± 1 SD or median (range), depending on their normal or skewed distribution provided by Shapiro-Wilk's W test. Spearman's rank order regression analysis was used for testing relationships among the variables of interest. Between-group comparisons were performed by means of Mann-Whitney's U test.

Results

Predialysis serum levels of the markers studied were: AT 1.46 ± 0.35 g/L (reference value, 1.10–2.30 g/L), C3 1.03 ± 0.29 g/L (reference, 1.20–2.30 g/L), and C4 0.39 ± 0.15 g/L (reference, 0.20–0.40 g/L). Concentrations of the established inflammatory markers were: CRP 8 (5–91) mg/L (normal value, <10 mg/L), fibrinogen 304 (170–548) mg/dL (reference, 150–350 mg/dL), α₁ acid-glycoprotein 1.01 (0.54–3.46) g/L (reference, 0.30–1.30 g/L), albumin 3.74 ± 0.46 g/dL (normal value, ≥ 3.5 g/dL), lipoprotein (a) 14.2 (0–93.3) mg/dL (reference, a median of 7 mg/dL), and vWF:Ag 125 (60.5–246)% (reference, 60–150%).

On bivariate regression analysis (Table 1), serum AT showed clinically consistent direct associations with CRP, fibrinogen, α₁ acid-glycoprotein, lipoprotein (a) and vWF:Ag, and tended to be inversely related to albumin. There were no statistically significant associations between C3 or C4 levels and those of the other inflammatory reactants, except for a weak positive correlation between C4 and fibrinogen.

Table 1. Spearman's correlation coefficients among inflammatory markers in HD patients

	AT	C3	C4	CRP	AGP	Fibrinogen	Albumin	Lp(a)
C3	−0.036
C4	−0.028	0.202
CRP	0.331c	0.063	0.110
AGP	0.360c	0.216	0.047	0.506d
Fibrinogen	0.222a	0.109	0.240a	0.392d	0.438d
Albumin	−0.160	−0.154	−0.118	−0.249a	−0.170	−0.184
Lp(a)	0.265b	0.182	0.113	0.173	0.205	0.008	−0.118
vWF:Ag	0.243a	0.074	0.128	0.240a	0.241a	0.394d	−0.227a	0.138

AGP = α₁ acid-glycoprotein, AT = α₁-antitrypsin, CRP = C-reactive protein; Lp(a) = lipoprotein(a); vWF:Ag = von Willebrand factor antigen.

^aP<0.05.

^bP<0.01.

^cP < 0.005.

^dP<0.0001.

When the patients were stratified by the CRP and albumin levels (Table 2), the mean AT value in 17 patients with CRP ≥ 10 mg/L and albumin <3.5 g/dL was 26% higher than that in 45 patients with normal levels of these inflammatory markers (P = 0.008). Three patients (18%) in the former group had AT levels above the upper limit of normal range of 1.10–2.30 g/L, and none of the subjects in the latter group had elevated AT levels.

Table 2. Serum α₁-antitrypsin levels in HD patients stratified by the presence of inflammation

	α1-Antitrypsin (g/L)
	CRP<10 mg/L, albumin ≥ 3.5 g/dL	CRP ≥ 10 mg/L, albumin<3.5 g/dL
n	45	17
Mean	1.38	1.74
Standard deviation	0.27	0.50
Range	0.76–1.83	1.12–2.86
95% CIa	1.30–1.47	1.48–2.00

Reference values: α₁-antitrypsin, 1.1–2.3 g/L.

^a95% confidence interval of the mean.

Discussion

This study shows that serum AT level, but not those of complement components C3 and C4, could be a marker of chronic inflammation in maintenance HD patients.

Serum AT, a positive acute-phase reactant[[12]], [[13]] was found to be consistently associated with established markers of chronic inflammation in our HD patients. It directly correlated with increased CRP, fibrinogen, α₁ acid-glycoprotein, lipoprotein (a) and vWF:Ag, and tended to be inversely related to serum albumin concentrations. To determine whether serum AT level could select the inflammation-afflicted HD patients from those without this condition, we used CRP and albumin levels as discriminate variables. Increased CRP and hypoalbuminemia have been established as the most important inflammatory predictors of both all-cause and cardiovascular mortality in chronic HD patients.[[3]], [[4]], [[5]] In our study, at least 95% of the patients with such defined chronic inflammatory state had the AT level above 1.48 g/L, while the same percentage of no inflammation-afflicted HD subjects presented with the value below 1.47 g/L. Having used the cut-off point of 1.48 g/L, the positive predictive value of serum AT level on the presence of severe inflammation was 0.83, and the negative predictive value was 0.38. The sensitivity of this test was 65%, and its specificity was 63%. When we used the mean AT levels of 1.38 g/L and 1.74 g/L, the positive and negative predictive values became 0.86 and 0.62, respectively. Then, the sensitivity of this estimation increased to 86%, and its specificity to 73%.

In conclusion, serum levels of the long-lived, positive acute-phase reactant AT are helpful in diagnosing chronic inflammation in maintenance HD patients. The AT levels above 1.74 g/L and below 1.38 g/L may differentiate the HD patients with severe inflammation from those without. Further studies are required to determine why serum levels of complement components C3 and C4 are not diagnostic in this situation.