Mean platelet volume in pediatric chronic kidney diseases

To the editor

Mean platelet volume (MPV) is the most commonly used measure of platelet size and a useful platelet function index that can show platelet activation and its production rate in bone marrow [1], [2]. MPV has been studied in various disease groups other than hematologic disease, and we have reported this platelet index in hepatic diseases and acute ischemic stroke [1], [2]. It has been suggested that high-grade systemic inflammatory diseases, such as rheumatoid arthritis, present with low levels of MPV [3]. However, there were some needs to evaluate MPV in low-grade or localized inflammatory diseases. Therefore, to investigate MPV in chronic localized inflammation such as glomerulonephritis, we planned to investigate MPV in Korean pediatric patients with chronic kidney diseases (CKD).

This study was done at Kyung Hee University Hospital, a tertiary teaching hospital, between January 2011 and February 2012. The study included total 200 individuals for patients group, which were subdivided into 71 with IgA nephropathy (IgAN), 52 with mesangeal proliferative glomerulonephritis (MesPGN), and 77 with nephrotic syndrome (NS). The diagnosis and classification of CKD were based on renal biopsy results and clinical criteria. Since it was not easy to recruit normal pediatric patients from those who visited the pediatric department of our hospital, we had to compare MPVs with a disease control that had inflammatory signs in the upper respiratory tract (URT). Seventy pediatric patients with acute inflammatory symptoms in regions of URT were enrolled for age-matched disease controls (Table 1). Mean age of patient group was 11.64 (range 2–20 years), and male to female ratio was 75:125. Blood sampling was performed through venepuncture and MPV was measured using EDTA-containing tubes in Advia 2120 (Bayer Diagnostics, Tarrytown, NY, USA) within 2 hours. ANOVA followed by post-hoc analysis were used to compare means in our study. The statistical analyses were performed with MedCalc v11.6 (MedCalc Software, Mariakerke, Belgium) and Excel 2007 (Microsoft corporation, Redmond, WA). Statistical significance was set at p < 0.05.

Table 1.  Patient compositions and disease entities.

Total number of patients	270
Subgroup
I. Patient group	200
1. IgA nephropathy	71
2. Mesangeal proliferative glomerulonephritis	52
3. Nephrotic syndrome	73
II. Control group	70
Acute nasopharyngitis	21
Acute pharyngitis	16
Acute bronchitis/bronchiolitis	13
Acute sinusitis	4
Allergic rhinitis	4
Acute lymphadenitis of face,head and neck	4
Acute obstructive laryngitis	4
Etc.*	4

*Acute tonsillitis, acute suppurative otitis media, acute upper respiratory infection, unspecified.

Based on the comparison of MPV between one disease control and three CKD groups, a significant difference was observed (Figure 1): MPV was markedly increased in IgAN and MesPGN than the other two groups (p = 0.01).

Figure 1. Mean platelet volume (MPV) was markedly increased in IgA nephropathy (IgAN) and mesangeal proliferative glomerulonephritis (MesPGN) comparing with acute respiratory illness (Control) and nephrotic syndrome (Nephrotic S, p = 0.01).

Several cytokines, inflammatory mediators and growth factors may affect MPV, with subsequent production of larger and more reactive platelets [1], [3–6]. Because bone marrow might be exposed longer in chronic inflammation than acute conditions, inflammatory mediators have more time to make an impact upon platelet size. In this study, we were able to compare the change in MPVs between chronic and acute inflammation types by designating a patient group that showed acute inflammatory symptom and signs in the URT as the control group. Also, we confirmed whether there are meaningful differences in MPVs at IgAN and MesPGN that are known to show more frequent inflammatory findings such as cell proliferations, based on pathologic findings in renal biopsy. In such circumstances, MPV showed increased levels in IgAN and MesPGN than NS and acute diseases like upper respiratory infection. Therefore, we carefully suggest that the type, duration or degree of inflammation may affect the levels of MPV.

However, we also note that there were some limitations to our study. First, subjects in the control group were not healthy individuals but subjects with acute inflammatory symptoms in URT. Second, patients were under the care of a nephrologist, and had been treated with specific regimen. Therefore, effects of drugs such as steroid on MPV were not excluded in this study. In a further study, the association analysis between MPV and the new renal marker such as cystatin C or neutrophil gelatinase-associated lipocalin (NGAL) could provide more information about the meaning of MPV changes in CKD. Moreover, it should be noted that MPV can reflect the degree of inflammatory state, disease progression or therapy response in various renal diseases. Also, further research should try to identify whether there is a preceding meaningful change in the cytokine levels for diseases with increased MPV.