HAEMATOLOGICAL INDICES AND THEIR ASSOCIATION WITH FLUID BALANCE, INFLAMMATION, AND CLINICAL OUTCOMES IN HOSPITALIZED MEDICAL PATIENTS

Background: Haematological indices reflect erythrocyte morphology, haemoglobin content, and red blood cell production. These indices are influenced by nutritional status, inflammation, and fluid balance. The hematocrit-to-haemoglobin ratio (HHR) has been validated as a marker of haemodilution (HHR <3) and haemoconcentration (HHR ≥3). However, the interplay between haematological indices, fluid balance, inflammation, and clinical outcomes has not been comprehensively evaluated.
Objective: To evaluate the association between haematological indices, fluid balance status, inflammatory status, and clinical outcomes in hospitalized medical patients.
Methods: A retrospective observational cohort study was conducted at King Hussein Medical Center, Jordan. Adult patients (≥18 years) admitted to internal medicine departments between February 2021 and November 2025, with complete CBC data on admission, were included. Data extracted included demographics, MCHC, MCH, MCV, RDW, haemoglobin, haematocrit, HHR, SII, NLR, albumin, GNRI, HALP, length of stay, ICU transfer, mechanical ventilation, and mortality. Cluster analysis identified distinct clinical phenotypes.
Results: Among 847 patients (mean age 68.4±14.2 years, 54.6% male), haemodilution (HHR <3) was present in 48.6% (n=412). Abnormal indices were prevalent: elevated RDW (>14.5%) in 62.4%, low MCHC (<32 g/dL) in 34.8%, low MCH (<27 pg) in 28.6%, elevated MCV (>100 fL) in 18.4%, and anaemia in 58.2%. Cluster analysis identified four phenotypes: (1) normal indices + normal HHR (25.4%), (2) anaemia + haemodilution + elevated RDW (31.2%), (3) microcytic + haemodilution (22.8%), and (4) macrocytic + hemoconcentration (20.6%). Phenotype 2 had the highest mortality (12.8%), followed by phenotype 4 (10.2%), phenotype 3 (6.8%), and phenotype 1 (3.2%) (p<0.001). Independent mortality predictors included elevated RDW (OR=2.45), low MCHC (OR=1.92), haemodilution (OR=1.85), elevated SII (OR=1.78), and hypoalbuminemia (OR=1.68). A haematological risk score (RDW, MCHC, HHR, SII) demonstrated good discrimination (AUC=0.79, 95% CI: 0.74–0.84).
Conclusion: Haematological indices, particularly elevated RDW, low MCHC, and abnormal fluid balance (HHR <3), are independently associated with adverse outcomes. Cluster analysis identified distinct clinical phenotypes with different mortality risks. A simple haematological risk score may aid in risk stratification.