A study of diagnostic utility of serum ischemia modified albumin and IMA index in ischemic stroke and hemorrhagic stroke patients

Sarika Argade¹, Reshakiran J Shendye^2*

Abstract               Background: Stroke is associated with high morbidity and mortality rates, however, biochemical markers to aid in its early detection are lacking.As Ischemia Modified Albumin (IMA) is a novel marker for ischemia and previous studies have shown that its level increases acutely after ischemic stroke. Hence, it can be used to differentiate ischemic stroke from hemorrhagic and timely management of these patients. Objective: To compare levels of serum Ischemia Modified Albumin (IMA) in patients with ischemic and hemorrhagic stroke. Methods: Present cross sectional study comprised of 90 subjects, 30 ischemic stroke, 30 hemorrhagic stroke (definitive diagnosis based on radiological images) and 30 as apparently healthy control. Blood samples obtained within 24 hours of presentation were analysed for albumin by BCG dye binding method, IMA by albumin cobalt binding assay and albumin adjusted IMA index using formula by Lippi et al. Result: IMA concentrations were 0.340 ± 0.10 absorbance unit (ABSU) in control group, 0.45 ± 0.09ABSU in ischemic stroke and 0.38 ± 0.08ABSU in hemorrhagic stroke which were statistically higher (p< 0.0001) among stroke group as compared to control. There was also statistical significant difference (p< 0.003) of IMA concentrations between ischemic stroke and hemorrhagic stroke. A significant negative correlation between IMA and serum albumin (r = -0.75, p < 0.05) was observed. IMA index were 0.32±0.07 ABSU, 0.43±0.06 ABSU, 0.37±0.05 ABSU in control, ischemic and hemorrhagic stroke respectively and was highly significantly raised (p<0.0001) in ischemic stroke compared to hemorrhagic stroke and control. Conclusion: It is observed that IMA is a potential marker in diagnosing acute ischemia in cerebrovascular diseases as well as in differentiating types of stroke.

Key Word: ischemic stroke, hemorrhagic stroke, ischemia modified albumin, albumin adjusted IMA index.

INTRODUCTION

Stroke is one of the leading causes of mortality and morbidity in adults worldwide, posing serious medical, socio-economic and rehabilitation problems. It is the third leading cause of death in the developed countries after cardiovascular diseases and cancer¹. Stroke is defined by World Health Organization (W.H.O.) as clinical syndrome consisting of “rapidly developing clinical signs of focal (at times global) disturbance of cerebral function, lasting more than 24 hours or leading to death with no apparent cause other than that of vascular origin.” Every year new acute strokes cases are 1.44 to 1.64 million and DALY that were lost, almost amounted to 6.3 million². Stroke is classified on the basis of its etiology as either ischemic or hemorrhagic. Ischemic stroke is caused by occlusion of a cerebral artery through thrombosis or embolism, while hemorrhagic stroke is caused by rupture of a cerebral artery which leads to bleeding directly into or around the brain. Despite the two types sharing similar risk profiles, they exhibit distinct molecular mechanisms in the acute phase. In the diagnosis of patients with acute stroke presenting to the emergency department, clinicians face difficulties many times as diagnosis is mainly based on history, clinical examination and correlating radiological findings. But acute brain infarction generally exhibits no radiological findings in the early stage. Brain Computed Tomography (CT) scans obtained in the first several hours after an infarction generally shows no abnormality, and the infarct may not be seen reliably for 24–48 hours³. Though diffusion weighted magnetic resonance imaging (MRI), CT perfusion of brain and cerebral angiography can confirm the diagnosis at this early stage⁴ but such facilities are not available widely, time consuming, and very costly. Use of biochemical markers of cerebral ischemia can be a newly favoured approach for early diagnosis of ischemic stroke and can be a supplement to neuro-imaging techniques. One of such marker of interest is ischemia modified albumin (IMA). Human serum albumin is one of the most important circulating antioxidant present in blood which is exposed to continuous oxidative stress and thus, has a role in efficient antioxidant defence mechanism of the organisms⁵. Overproduction of free radicals in conditions like oxidative stress, during ischemia –reperfusion, hypoxia and acidosis alter the N-terminus of serum albumin and reduce its ability to bind Co²⁺ and Ni²⁺. This altered form is referred to as ischemia modified albumin (IMA). Following a period of ischemia, a reduction in the ability of albumin to bind cobalt is apparent. This is the basis of the albumin cobalt binding test (ACB® test) for IMA⁶. Some studies have observed that IMA results reflect albumin concentrations rather than ischemia when albumin concentration is less than 3.4g/dl⁷. Hence, to overcome the effect of serum albumin concentration on IMA, albumin-adjusted ischemia-modified albumin index (IMA index) is proposed. It is calculated by using IMA, albumin level and median albumin level of population⁸. IMA, a new biochemical marker is used to rule out myocardial ischemia and has been approved by the US Food and Drug Administration⁶. However, the utility of IMA and albumin adjusted IMA index to differentiate between ischemic and hemorrhagic stroke is still under study. So the present study is planned to compare serum IMA and albumin adjusted IMA index in ischemic and hemorrhagic stroke patients presenting to the casualty.

 MATERIALS AND METHOD

Present cross sectional study including 90 subjects, 30 ischemic stroke, 30 hemorrhagic stroke (definitive diagnosis based on radiological images) and 30 as apparently healthy control, was carried out in our institute. The study design and protocol has been approved by the institutional ethical committee. In this cross sectional study, subjects with age group 18 years to 60 years were chosen randomly irrespective of their sex amongst newly diagnosed patients of acute stroke admitted within first 24 hours of stroke onset in medicine wards. The diagnosis was confirmed by clinical signs, symptom and CT scan or MRI brain. On the basis of radiological findings they were divided into two study groups, ischemic and hemorrhagic stroke 30 cases each and compared with 30 apparently healthy controls.

Inclusion criteria: Patients of age 18-60 years who had developed a first ever stroke that is a neurological deficit of cerebrovascular cause which persists beyond 24 hours were included in the present study.

Exclusion criteria: Stroke patients admitted after 24 hours of symptom onset and transient ischemic attack, cardiac diseases, cancer, infections, end stage renal disease, liver disease, uncontrolled diabetes mellitus and history of treatment of thyroid disease were excluded. Details and purpose of study was explained and a signed informed consent was obtained as per the proforma from all the subjects or their legally responsible attendant.

Collection: About 5 ml of blood sample was withdrawn from the ante-cubital vein of each participant taking all aseptic precautions and blood was transferred to a clean dry sterile plain vacutainer. Blood specimen in plain tubes were allowed to clot for 30 minutes and then centrifuged and serum samples were stored in aliquots at -20°C till the time of estimation of IMA.

METHOD

RESULT

90 subjects were studied on the basis of inclusion and exclusion criteria. Base line characteristics of the study groups were similar and shown in table 1.

Table 1: Base line characteristics of the study group

Table 2: Comparison of serum IMA and albumin adjusted IMA index

Table 3: Comparison of serum IMA and albumin adjusted IMA index between two study groups

The IMA values were highly significantly raised in ischemic stroke as compared to control group (p-value < 0.0001), while there was significantly increased value in ischemic stroke compared to hemorrhagic stroke (p-value < 0.05). But there was no significant increase in IMA values in hemorrhagic stroke group compared to control (p-value > 0.05). In the present study a significant negative correlation between IMA and serum albumin (r = -0.75, p < 0.05) was observed. Hence, to overcome the effect of albumin on IMA value, albumin adjusted IMA index was calculated and IMA index was significantly higher in ischemic stroke than control and hemorrhagic stroke group (p< 0.0001).

Figure 1: Correlation of IMA with serum albumin.Figure 2: comparison of IMA and albumin adjusted IMA index

ROC curve analysis for IMA shows that area under curve is 0.690. The optimum diagnostic cut-off is 0.310 ABSU and has 86.4% sensitivity, 53.3% specificity, 78.5% positive predictive value and 66.7% negative predictive value. ROC curve for albumin adjusted IMA index shows that area under curve is 0.804. The optimum diagnostic cut-off is 0.374 ABSU and has 73% sensitivity, 77 % specificity, 86% positive predictive value and 59% negative predictive value. Thus, IMA index was found to be less sensitive but more specific than serum IMA levels in the study.

Figure 3: ROC curve for IMA,Figure 4:ROC curve for albumin adjusted IMA index

DISCUSSION

Ischemia-modified albumin is a nonspecific marker of tissue ischemia, which has been studied extensively in patients with acute chest pain¹⁰. The Albumin Cobalt Binding test used for IMA estimation is the US FDA approved assay for myocardial ischemia. Extracardiac oxidative stress may elevate IMA levels. Gunduz et al determined elevated IMA levels in mesenteric ischemia¹¹; and Turedi et al, in pulmonary embolism¹². Ischemia-modified albumin is also elevated in patients with skeletal muscle ischemia¹³. Abboud H et al. suggested that IMA levels may be a promising biomarker for early identification of acute stroke. They observed that IMA levels increased during the first 24 hours in brain infarction patients, whereas no change was seen in intracranial hemorrhage patients¹⁴. Kun han et al. also found increased serum IMA levels following an acute cerebrovascular event¹⁵. The results of present study are in agreement with these studies as in the present study the IMA levels were highly significantly elevated in stroke cases compared to control. On comparison between two groups highly significant increase in IMA levels was seen in ischemic stroke group than control and significant increase compared to hemorrhagic stroke. During ischemia/reperfusion, as the result of acidosis, reduced oxygen tension, and the generation of free radicals, modifications of N- terminal residues of albumin occur. The NH2-terminal of human serum albumin is known to be a binding site for transition metal ions such as cobalt, copper and nickel. Hypoxia as a result of lack of blood supply decreases its metal binding ability and leads to formation of ischemia modified albumin. David Bar-Or et al utilized this property of IMA and framed a rapid and simple colorimetric test, Albumin Cobalt Binding (ACB) test to evaluate the extent of ischemia ⁶. In addition, some studies suggested that IMA results reflect albumin concentrations rather than ischemia ⁷. Present study also demonstrated that IMA level is dependent on serum albumin concentration and a negative correlation was observed between serum ischemia modified albumin and serum albumin concentration. This finding is in agreement with the study of Hakligor et al which suggested that ischemia modified albumin levels determined in patients with albumin concentrations less than 3.4g/L should be interpreted with some caution. In order to nullify the effect of serum albumin level on IMA estimation, Lippy et al proposed albumin adjusted IMA index. It is calculated using serum IMA value and albumin concentration⁸. Albumin adjusted IMA index was significantly higher in ischemic stroke than hemorrhagic and controls. In this study, comparison of IMA and albumin adjusted IMA index in the diagnosis of AMI showed that IMA index has better specificity and PPV than IMA. On the other hand, sensitivity was higher in the case of IMA which could be because of higher false negative values in albumin adjusted IMA index due to over correction for samples with lower albumin concentration. . This study has several potential limitations. Sample size in each group was small and this might have reduced the accuracy of sensitivity, specificity, NPV and PPV used to compare diagnostic value. Though, in the present study control and stroke group had patients with lower as well as higher serum albumin levels than the median value, but, comparatively the number of patients with lower albumin level than median was slightly more. So, a larger study with equal number of patients with albumin concentration lower and higher than median value should be conducted to determine the diagnostic value of IMA index over IMA in the diagnosis of ischemic stroke.

CONCLUSION

Thus, from the present study it can be concluded that IMA, as one of the biomarker for ischemia, is more sensitive in diagnosing acute ischemia in stroke patients as well as to differentiate types of stroke. A negative correlation was observed between serum IMA level and albumin concentration and hence, albumin adjusted IMA index calculated was found to be a better than IMA in diagnosing ischemic stroke as it showed higher specificity and PPV.on the other hand being an economic and easy to perform assay, it can assist clinical diagnosis where neurological imaging facilities are not available.

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