European Journal of Cardiovascular Medicine

Pleural effusion represents an abnormal accumulation of fluid within the pleural space and laboratory assessment plays a pivotal role in establishing the diagnosis, determining the underlying etiology, and guiding management.¹ Once pleural effusion is suspected clinically and confirmed radiologically, laboratory evaluation begins with baseline blood investigations, including complete blood count, erythrocyte sedimentation rate, C-reactive protein, renal and liver function tests, and serum protein and lactate dehydrogenase (LDH) levels.² These tests provide supportive information regarding infection, inflammation, organ dysfunction, and systemic diseases contributing to pleural fluid accumulation. Diagnostic thoracentesis is the cornerstone of laboratory assessment and is indicated in most cases of new-onset pleural effusion, except when the cause is clinically obvious, such as uncomplicated congestive heart failure.Pleural fluid obtained by thoracentesis is subjected to a systematic laboratory analysis³. Gross examination of the fluid offers initial clues; clear straw-colored fluid is commonly seen in transudates, while turbid or purulent fluid suggests infection. Hemorrhagic fluid may indicate malignancy, trauma, or pulmonary embolism, whereas milky fluid raises suspicion of chylothorax.⁴ Biochemical analysis of pleural fluid includes measurement of protein, LDH, glucose, pH, and adenosine deaminase (ADA). These parameters are interpreted alongside corresponding serum values, most importantly through Light’s criteria, which differentiate transudative from exudative effusions.⁵ Exudative effusions indicate increased pleural membrane permeability and are commonly associated with infections, malignancy, and inflammatory conditions.Cell count and differential analysis further aid etiological diagnosis. A predominance of neutrophils suggests acute processes such as parapneumonic effusion or empyema, whereas lymphocyte-rich effusions are more commonly associated with tuberculosis, malignancy, or chronic inflammatory disorders. Eosinophilia in pleural fluid may be seen in air or blood in the pleural space, drug reactions, or parasitic infections.⁶ Microbiological examination, including Gram stain, acid-fast bacilli staining, culture, and molecular tests, is essential for identifying bacterial and tubercular causes. Measurement of ADA levels is particularly valuable in diagnosing tuberculous pleural effusion in endemic regions, with higher levels strongly supporting the diagnosis.Cytological examination of pleural fluid is crucial when malignancy is suspected.⁷ Detection of malignant cells confirms malignant pleural effusion and helps guide further oncological evaluation and management.

AIM

To evaluate the  laboratory findings, and etiological spectrum of pleural effusion in patients.

The present study was conducted in the Department of Medicine at S.P. Medical College and P.B.M. Associated Group of Hospitals, Bikaner, over a defined study period. It was designed as a cross-sectional, hospital-based study carried out at a tertiary care centre. The study population comprised adult patients admitted to the medicine wards in whom pleural effusion was detected during routine clinical examination and/or radiological investigations. A total of one hundred consecutive patients with pleural effusion who provided informed consent were included in the study. Inclusion criteria consisted of adult patients aged more than 18 years with clinically and/or radiologically confirmed pleural effusion. Patients who were unwilling to participate in the study were excluded. All enrolled patients underwent detailed  laboratory investigations, including routine  biochemical analysis, and pleural fluid examination as per standard protocols, to determine the etiology of pleural effusion.

Table 1:Distribution of cases according to Gender

Out of total 26 right sided group cases, 17 were males and 9 were females, out of 21 left sided cases, 15 and 6 were males and females respectively while out of 53 bilateral pleural group cases, 39 and 14 were male and females respectively and the difference was found statistically insignificant (p>0.05).

Table 2:Distribution of cases according to past history

Comorbidities were variably distributed across pleural effusion types with predominance of bilateral involvement, and only chronic kidney disease and chronic liver disease showed a statistically significant association (p < 0.05).

Table 3:Statistical analysis of different parameters of hemogram

Hematological analysis showed no significant difference in total leukocyte count and neutrophils, while lymphocytes, monocytes, eosinophils, hematocrit, MCH, and plateletcrit varied significantly across pleural effusion groups, with other indices remaining comparable.

Table 4:Statistical analysis of different biochemical parameters

Biochemical analysis showed no significant difference in serum sodium, albumin, and random blood sugar, while serum potassium, total protein, and ESR varied significantly among pleural effusion groups (p < 0.05).

Table 5:Distribution of cases according to serum creatinine (mg/dl)

Raised serum creatinine was seen in 26% of patients, mainly with bilateral pleural effusion, and mean levels were significantly higher in this group compared to right- and left-sided effusions (p < 0.01).

Table 6:Statistical analysis of cytological and biochemical parameters of pleural effusion

Pleural fluid analysis revealed a significant difference in total cell count and mesothelial cell percentage among effusion types, while lymphocyte and polymorph predominance and pleural fluid–serum LDH and protein ratios showed no significant variation (p > 0.05).

Table 7:

Serum LDH levels were comparably distributed across right-sided, left-sided, and bilateral pleural effusion groups, with no statistically significant difference in mean values among the groups (p > 0.05).

Table 8:Distribution of cases according to ADA (IU/L)

As shown in the table, ADA levels varied widely, with nearly half of the cases having values <30 IU/L, while mean ADA was significantly higher in left-sided pleural effusion compared to right-sided and bilateral effusions (p < 0.001).

Table 9:Distribution of cases according to trans/exudative

In the present study, transudative and exudative pleural effusions were distributed across right-sided, left-sided, and bilateral groups without any statistically significant difference (p > 0.05).

In the present study, pleural effusion was more commonly observed in males across right-sided, left-sided, and bilateral groups; however, the gender-wise distribution did not show a statistically significant difference (p > 0.05). Overall, males predominated with a male-to-female ratio of 2.45:1, indicating a higher occurrence of pleural effusion among male patients.Similar study done by Sharma and Mohan8 on 200 cases and they found that male predominance over female with male to female ratio was 2:1 which is quite similar to our results.

In the present study, comorbidities such as hypertension, diabetes mellitus, prior blood transfusion, tuberculosis, and chronic liver disease were variably distributed among right-sided, left-sided, and bilateral pleural effusion groups, with a predominance of bilateral involvement in conditions like hypertension, diabetes, and chronic kidney disease. All cases of chronic kidney disease were associated with bilateral pleural effusion, while other conditions showed no specific laterality, and bronchial asthma was noted in only one patient with left-sided pleural effusion.

In the present study, out of total 100 cases, 74 patients had their serum creatinine level within normal range while 26 cases had raised serum creatinine and out of them 2, 4 and 20 cases belonged to right sided, left sided and bilateral pleural effusion groups respectively. Mean serum creatinine in right sided pleural effusion group was 0.86±0.37 mg/dl, in left sided pleural effusion group it was 1.16±0.62 mg/dl and in bilateral pleural effusion group it was 2.68±2.85 mg/dl and this difference was found statistically significant (p<0.01).

In present study, mean serum LDH (U/L) in right sided pleural effusion group was 697.85±212.74, in left sided pleural effusion group it was 694.38±139.64 and in bilateral pleural effusion group it was 673.55±321.42 and this difference was found statistically insignificant (p>0.05).

In the present study, mean total leukocyte count and neutrophil percentage did not show any statistically significant difference among right-sided, left-sided, and bilateral pleural effusion groups.Lymphocyte percentage varied significantly across the groups, with lower values noted in left-sided effusions (p < 0.05).Monocyte percentage showed a highly significant increase in bilateral pleural effusion cases (p < 0.01).Eosinophil counts also differed significantly, being relatively higher in right-sided effusions (p < 0.05).Hematocrit and mean corpuscular hemoglobin demonstrated statistically significant differences among the groups, whereas mean corpuscular volume, mean corpuscular hemoglobin concentration, and mean platelet volume were comparable.Plateletcrit showed a significant reduction in bilateral pleural effusion, while other platelet indices remained statistically insignificant.

Analysis of biochemical parameters showed no statistically significant difference in mean serum sodium, serum albumin, and random blood sugar levels among right-sided, left-sided, and bilateral pleural effusion groups.However, mean serum potassium, total protein, and ESR varied significantly across the groups, with higher potassium levels and altered protein and ESR values particularly noted in bilateral pleural effusion (p < 0.05).

Serum albumin levels remained comparable across all groups, suggesting no significant variation in nutritional or chronic inflammatory status.Random blood sugar values also did not differ significantly among the three groups.Additionally, bilateral pleural effusion was observed in six cases and left-sided effusion in four cases, with associated conditions such as cholelithiasis and silicotuberculosis showing no statistically significant association (p > 0.05).

Analysis of pleural fluid parameters revealed a statistically significant difference in mean total cell count among right-sided, left-sided, and bilateral pleural effusion groups, with the highest count observed in left-sided effusions (p < 0.05).Lymphocyte predominance was noted in most cases, with 89% of patients having a lymphocyte count of 50% or more, and no significant difference in lymphocyte percentage among the three groups.

Polymorph predominance was observed in a small proportion of cases (9%), with no statistically significant variation across the groups.Mesothelial cell percentage showed a highly significant difference, being markedly higher in left-sided pleural effusions (p < 0.001).The pleural fluid–serum LDH ratio did not differ significantly among right-sided, left-sided, and bilateral effusions.Similarly, the pleural fluid–serum protein ratio remained comparable across all groups, showing no statistically significant difference.Similar study was observed by Maikap et al⁸ where they found 9(3.6%) cases have predominantly polymorphs in pleural effusion out of which 6 were due to parapneumonic and one each due to tubercular, rheumatoid arthritis and pancreatitis.

In the present study, pleural fluid ADA levels varied widely, with 49% of cases showing values <30 IU/L, while a substantial proportion had elevated ADA levels, including 34% with values >60 IU/L. The mean ADA level was significantly higher in left-sided pleural effusion compared to right-sided and bilateral effusions, and this difference was statistically highly significant (p < 0.001).A study conducted by Maikap et al⁸ found that 77.3% of tubercular pleural effusions had pleural fluid ADA (IU/L) level above 70 U/L. They found presence of malignant cell in pleural fluid in 48.57% of cases of pleural effusion due to malignancy which is consistent with findings of Light.

In present study, out of total 52 transudative cases, 12, 7 and 33 cases belonged to right sided, left sided and bilateral pleural effusion groups respectively while out of total 48 exudative cases 14, 14 and 20 cases belonged to right sided, left sided and bilateral pleural effusion groups respectively and the difference in both transudative and exudative was found statistically insignificant (p>0.05).Study conducted by Sharma et al⁹ found that most of the pleural fluids were exudates (89/104, 85.57 %) with Tuberculosis and Malignancy as two most common etiologies.

The present study demonstrates that pleural effusion is more common in males, with a clear male predominance, although gender distribution did not show a statistically significant association with laterality. Bilateral pleural effusion was the most frequent presentation and was commonly associated with systemic comorbidities, particularly chronic kidney disease, which showed a statistically significant association. Laboratory evaluation revealed selective hematological and biochemical variations across different types of pleural effusion, with significant differences noted in lymphocyte, monocyte, eosinophil counts, serum potassium, total protein, ESR, and serum creatinine, especially in bilateral effusions. Pleural fluid analysis showed a predominance of lymphocytic effusions, with mesothelial cell count and total cell count showing significant variation based on laterality. Elevated ADA levels, particularly in left-sided effusions, strongly supported tubercular etiology, while transudative and exudative effusions were comparably distributed across laterality.

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