ABSTRACT | PDF

ORIGINAL ARTICLE

Mean platelet volume in anxiety disorder: a case-control study

Swapna Bondade1, Supriya2, Manjula Adinarayan3, Parineetha P Bhat4

1Department of Psychiatry, The Oxford Medical College, Hospital & Research Centre, Bangalore, Karnataka, India, 2Department of Biochemistry, The Oxford Medical College, Hospital & Research Centre, Bangalore, Karnataka, India, 3Department of Pathology, The Oxford Medical College, Hospital & Research Centre, Bangalore, Karnataka, India, 4Department of Biochemistry, The Oxford Medical College, Hospital & Research Centre, Bangalore, Karnataka, India

Abstract

Background: Anxiety disorders are one of the most common psychiatric disorders existing in the population. The association between stress and platelet activity has been envisaged by the researchers. Mean platelet volume (MPV) is considered as the marker and determinant of platelet function. Objective: To evaluate the MPV in anxiety disorder and to check for the association of MPV with severity of anxiety. Method: This was a hospital-based, descriptive, cross-sectional case-control study. One hundred and fourteen consecutive anxiety disorder patients were included in the study. Age and gender matched 70 subjects were taken as controls. The Hamilton rating scale for anxiety (HAM-A) and the Hamilton rating scale for depression (HAM-D) were assessed and complete blood count, MPV, and lipid profile were measured for all the subjects. Results: MPV values were more in anxiety disorder (9.844±1.33) than in controls (8.72±0.49) and this difference was statistically significant (p<0.001). There was negative correlation between MPV and platelet count, and there was a positive correlation between HAM-A scores and MPV. Conclusion: Increased MPV is associated with anxiety disorder. Future research should be planned to investigate the effect of MPV, anxiety disorder on cardiovascular diseases and the effect of anxiety treatment on MPV.

Keywords: Stress. Platelet Function. Cardiovascular Diseases.

Correspondence: Dr. Supriya, Department of Biochemistry, The Oxford Medical College, Hospital & Research Centre, Yadavanahalli, Attibele, Bangalore-562107, Karnataka, India. supriyaranjandr@gmail.com

Received: 29 March 2018

Revised: 26 October 2018

Accepted: 22 December 2018

Epub: 2 February 2019

INTRODUCTION

Anxiety disorders are among the most common class of mental disorders present in the general population. The estimated lifetime prevalence of anxiety disorder is more than 15%, while the 12-month prevalence is over ten per cent.[1]

Serotonin (5-hydroxytryptamine [5-HT]) is well-established neurotransmitter in the central nervous system (CNS). It plays a key role in anxiety disorder, depression, platelet aggregation, and regulation of vascular tone.[2] Researchers have recorded that a hyper-serotonergic state resulting from impaired serotonin transporter (5-HTT) function can cause an anxiety or fear response by stimulating the amygdala.[3] Several 5-HTT abnormalities have been detected in anxiety disorder, although results concerning the synaptic serotonin state are still disconsonant.[4,5] Platelet uptake of serotonin from the plasma is dependent on 5-HTT which has a role in neurotransmitter reuptake in CNS and is also essential to the platelet plasma membrane.[6] Scientists have promulgated, platelet activity is amplified by emotional stress and hypothesised that the actions of stressors on platelets may be a primary trigger in coronary events such as myocardial infarction (MI).[7]

Mean platelet volume (MPV) is a good guide of platelet activity and is a measure of platelet size. Increased MPV is considered to be closely linked with cardiovascular diseases (CVDs), like acute MI, ischaemic heart diseases, congestive heart failure, and a close affiliation exists between CVDs and anxiety disorders.[8,9] However, there are only few studies which have reported a relationship between MPV and anxiety disorder in the literature. As CNS is challenging to access, peripheral platelet models are usually used as pointers of central 5-HT metabolism; moreover, they are known to reflect central serotonergic function.[10] The objective of the study is to assess MPV in anxiety disorder and to check for the association of MPV with severity of anxiety.

METHODOLOGY

This was a hospital-based, descriptive, cross-sectional case-control study, conducted in the outpatient department (OPD) of Psychiatry of The Oxford Medical College, Hospital and Research Centre (TOMCH&RC) in the year 2016 for duration of three months. One hundred and fourteen consecutive patients in the age group of 18-65 years who were diagnosed to have anxiety disorder according to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria were included in the study. Age and gender matched 70 subjects who were hospital employees or relatives of the patients and did not have any psychiatric disease were taken as controls. Subjects who had seizure disorders, mental retardation, other psychiatric disorders, hypertension, hypercholesterolaemia, acute or chronic physical illnesses, pregnancy, or a history of any drug use during the last month, smoking and alcohol use were excluded from the study. Written informed consent was taken from the cases and controls. They were administered a semi-structured proforma to collect sociodemographic details, height, body weight; the Hamilton rating scale for anxiety (HAM-A) and the Hamilton rating scale for depression (HAM-D) were assessed by the psychiatrist in OPD. Complete blood count (CBC), MPV, and lipid profile were measured and recorded for each subject. The study was approved by the institutional ethics committee of TOMCH&RC.

Measurements

Hamilton rating scale for anxiety (HAM-A)

HAM-A is one of the instruments frequently used to evaluate anxiety. It is a screening tool for anxiety symptoms with 14 items. Each item is rated on a zero to four scale. Patients who had the score above 14 have the risk for anxiety. Score above 14 is considered as clinical anxiety present. Score below 14 no anxiety, 14-17 mild anxiety, 18-24 moderate anxiety, and 25-30 severe anxiety.[11]

Hamilton depression rating scale (HAM-D)

HAM-D has 21 items and is an observer rated screening tool. Ratings are made on the basis of clinical interview. Scores of seven and below is considered as normal, eight to 13 as mild depression,14-18 as moderate depression, 19-22 as severe depression, and 23 and above as very severe depression.[12]

Complete blood count and biochemical analysis

Five ml of blood was obtained from medial cubital vein by venepuncture avoiding haemolysis. Following a 12-hour fasting period, from each subject, blood samples were drawn. The first two ml venous blood was collected in sterile BD vacutainer tube with 5.4 mg of K2 ethylene diaminetetraacetic acid (EDTA) from BD Franklin Lakes NJ USA. CBC, including MPV, were determined using Sysmex XP-100: A1489 haematology analyser (Sysmex, India). In order to measure MPV reliably and to minimise the potential influence of anticoagulant (EDTA), blood samples were analysed within 60 minutes after venepuncture. MPV and platelet count were measured for all subjects. The reference range for MPV was between 6.9-10.8 fL. Remaining three ml of blood samples was collected in gel vacutainer. Samples were centrifuged after 30 minutes at 3000 rpm for ten minutes. All the analysis was carried on serum samples. Serum cholesterol was measured by CHOD-PAP method,[13,14] triglycerides by GPO-PAP method, high-density lipoproteins (HDL) by phosphotungstic acid method, and low-density lipoprotein (LDL) cholesterol (LDL-C), very-low-density lipoprotein (VLDL) cholesterol (VLDL-C) were calculated by using Friedwald’s equations.[15] All the blood samples were analysed at the same laboratory.

Statistical analysis

The data was analysed using SPSS for Windows version 16.0 software (SPSS Icn Chicago, IL, USA). Data were tested for normal distribution using Kolmogorov-Smirnov test. Results obtained were analysed using descriptive and inferential statistical methods. Chi-square test was used for categorical data and student t-test, analysis of variance (ANOVA) was used for continuous data. Logistic regression was used to identify the relationship between anxiety disorder and MPV. Pearson’s correlation was used to know the association of MPV, platelet count, and anxiety scores.

RESULTS

There was no statistical difference in the sociodemographic details and body mass index (BMI) of the cases and the controls (Table 1). Among the 114 cases of anxiety disorder, 58% were generalized anxiety disorder (GAD), 26% were panic disorder (PD), and 16% were social anxiety disorder (SAD). HAM-A and HAM-D mean scores were higher in cases than controls and this difference was statistically significant (Table 2). There was no statistically significant difference in the lipid profiles and haemoglobin levels between the groups. MPV was more in anxiety disorder (9.844±1.33) than in controls (8.72±0.49) and this difference was statistically significant (p<0.001) (Table 2). When we compared MPV within the group, the value in SAD (10.98±1.42) was more than GAD (9.345±1.5) and PD (9.2±0.86), and this difference was statistically significant (p<0.05) (Table 3). When we compared MPV and platelet count with different grading of anxiety according to HAM-A in cases, there was no statistical difference in MPV and platelet count (Table 4). There was no statistical difference in MPV values between male (10.11±1.57) and female (9.76±1.27) cases (Table 5). There was negative correlation between MPV and platelet count (r value was -0.057) and there was a positive correlation between HAM-A scores and MPV (r value was +0.235) (Table 6). The odds of anxiety disorder was greater (odds ratio [OR]=4.123, p<0.001, confidence interval [CI]=2.472-6.876) with increasing MPV.

DISCUSSION

Platelets express 5-HT2A receptors and 5-HTT identical to those present in the brain; so, it has been used in psychiatry as a peripheral model of serotonergic system.[16] It has been observed that platelet size, measured as MPV, correlates with platelets reactivity.[17] Three criteria have been speculated as determinants of platelet volume: age dependent course that can alter platelet size in circulation, diversity and maturity of bone marrow megakaryocyte population, and peripheral size-related sequestration of platelets.[18] There is affirmation that to a great extent MPV is determined during the time of megakaryocyte fragmentation into platelets.[19]

In the aetiology of mortality in CVDs, depression and anxiety disorders are one of the important factors.[20] Increased anxiety levels have been associated with higher risk for stroke independent of other risk factors.[21] It has been suggested that platelet activity is influenced by emotional stress and that coronary events such as MI may be provoked by these stressors.[7] In one study, it was observed that the presence of anxiety symptoms is associated with higher platelet reactivity in stable CVD patients and authors have also suggested that anxiety may be a better predictor of platelet reactivity than depression in patients with CVD.[22]

In the present study, we found increased MPV levels in patients with anxiety disorder compared to controls. Similar finding was found by Kokacya et al.[23] where they observed increased MPV values in PD patients compared to controls. It is known that patients with anxiety, depression, or disruptive behaviour disorder have increased catecholamine levels, sympathetic activity, and cortisol secretion.[24] In a study, it was found that increased sympathetic activity can cause higher MPV values.[25] With support of these reports, some researchers have hypothesised  that the sympathoadrenal activation may provoke platelets via 2-adrenoreceptor activation, which in turn activate shape change and thereby increases MPV.[26,27] Depressive and anxiety disorders are also connected with endothelial dysfunction, increased inflammatory cytokine levels, and platelet reactivation. Plasma platelets as in CNS has a role in serotonin synthesis, secretion, and reuptake.[28] Multiple changes in platelet parameters were reported in anxiety disorder in a study.[29] Decrease of 5-HTT in [3H]imipramine-binding sites of platelets and an increase in 5-HT2A receptor-binding sites on the surface of platelets were responsible for these changes.[30] Platelets in patients of anxiety disorders have shown abnormalities in 5-HT1A receptor functions and alterations in 5-HTT levels and activity.[31] Decreased platelet activity after treatment with the selective serotonin reuptake inhibitors (SSRIs) in patients with major depression has been observed in some studies.[32,33]

Contrary to our findings, Göğçegöz Gül et al.[9] found lower MPV levels in PD patients compared to the control group. The authors postulated that abnormal serotonin metabolism, such as changes in the functional state of serotonin receptors in platelets of PD patients can cause decreased MPV in PD patients. But, they could not give exact reason for the decreased MPV. As a vast number of studies have reported increased MPV in patients with major depression, we believe that increased MPV levels can be expected in anxiety patients.

In the current study, there was a negative correlation between MPV and platelet count. It has been previously reported that larger platelets have a greater mass, denser granules, and are more active than smaller platelets, enzymatically and metabolically.[34] They have a greater thrombotic potential caused by higher levels of intracellular thromboxane A2 and also express more pro-coagulant surface proteins such as P-selectin and Gp IIb/IIIa.[35] Additionally, larger platelets aggregate more rapidly than smaller platelets. Increase in platelet volume are often associated with decrease in platelet count perhaps as a result of small platelets being consumed in order to maintain a constant platelet functional mass.[26] In our study, we observed positive correlation between MPV and HAM-A score; this shows that as the anxiety score increases the MPV values increases. There is a paucity of literature with regard to this.

Gender related differences in platelet activity have been reported previously.[36] We found that MPV levels of male patients were higher than those of female patients; but, there was no statistically significant difference. Male and female patients had higher MPV than the controls and this difference was statistically significant. These findings may contribute to the independent association of MPV levels with anxiety disorder.

In our study, we observed that MPV was higher compared to controls and when the comparison was made within the group, it was observed that MPV was higher in SAD than GAD and PD, and this difference was statistically significant.

To the best of our knowledge, this is the first study in India to examine the relationship of MPV and anxiety disorder. The other studies done previously have not used scales to measure the severity of the anxiety symptoms and they could not correlate the severity of the disorder and the MPV, and had quoted as the limitation in their studies. Our analysis did not include individuals with conditions such as hypertension, coronary artery disease, diabetes mellitus, malignancy, dyslipidaemia, stroke, drug use, smoking and alcohol abuse which are known to affect platelet activity.

Despite the strengths of the study, there were certain limitations. As it is a hospital-based case-control study with small sample size, it could not be generalised to community. This study was a single centre study and not a multicentre study. Subclinical inflammation and pre-hypertensive state in the study subjects were not assessed and this can have influence on the MPV. Even though to reduce the influence of anticoagulant (EDTA), blood samples were analysed within 60 minutes after venepuncture, it still can have effect on MPV measures.

To conclude, increased MPV is associated with anxiety disorder. There was a positive correlation between MPV and severity of anxiety symptoms. Further research for the estimation of MPV as a tool for neuropsychiatry and psychopharmacology to examine how certain mental diseases and medications influence CNS is required. Studies to investigate the effect of MPV, anxiety disorder on CVDs and the effect of anxiety treatment on MPV should be carried out.

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Bondade S, Supriya, Adinarayan M, Bhat PP. Mean platelet volume in anxiety disorder: a case-control study. Open J Psychiatry Allied Sci. 2019 Feb 2. [Epub ahead of print]

Source of support: Nil. Declaration of interest: None.

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