Redblood Cell Distribution Width to Platelet Ratio (RPR): Novel diagnostic possibilities for perinatal disease in newborn foals
Abstract
Perinatal diseases are the leading cause of death among foals up to 7 days of age. Early
clinical signs of diseases in neonatal foals are often non-specific, and untreated foals
deteriorate rapidly. Therefore, early detection of the disease onset is essential. The
development of rapid and accurate markers to aid in diagnosing neonatal foals is needed.
The CBC parameters redblood cell distribution width (RDW) and RDW to platelet ratio
(RPR) have been used in human medicine as markers of inflammation in many diseases.
Therefore, the purpose of this work was to report the values of RDW and RPR in neonatal
foals and to investigate their possible correlation with a risk score based on obstetric and
clinical data. In this retrospective case-control study, 309 full-term Thoroughbred foals
less than 24h old were clinically evaluated within 15 minutes after birth, and blood
samples were collected within 24h of life. Foals showing an unremarkable physical
examination, normal gestational length (320 to 365 days), adequate righting reflexes, and
CBC values within the normal range were considered healthy. Foals that were born
through dystocia, displayed delayed adaptative milestones (sternal
recumbence > 5 minutes, suckling reflex > 20 minutes, stand >1 hour), gestational length
> 365 days, and/or displayed physical/hematological characteristics of dysmaturity (silky
hair-coat, domed head, floppy ears, abnormal granulocyte:lymphocyte ratio), were
categorized in the group at-risk. Extracted data were assessed for normal distribution
using the Shapiro-Wilk test. The Student’s T-test was used to evaluate the influence of
groups and foal sex on hematological variables (RBC, hematocrit, hemoglobin, MCV,
MCH, MCHC, RDW, platelets, WBC). Pearson's coefficient test was used to analyze the
associations between gestational length and RDW, and RPR. Continuous variables are
presented as mean ± SD. Categorical variables are presented as frequencies and
percentages. All statistical analysis was conducted in the statistical package R Studio,
and significance was set at P < 0.05. Based on the risk score, 221 (71.6%) foals were
healthy, and 88 (28.4%) were considered at risk of developing perinatal disease (at-risk
group). The mean gestational age for all the foals was 346.31 ± 9.69 days. RDW values
did not differ between groups. Gestational length demonstrated to have a negative
correlation with RDW (r = -0.156, P = 0.005) and MCV (r = -0.135, P = 0.01), indicating a
link of these variables to foal maturity. RPR was higher for at-risk (0.073 ± 0.018) than for
healthy foals (0.068 ± 0.014, P = 0.01). Therefore, the RPR ratio is a low-cost, readily
accessible index and might be a promising early indicator of disease for the field triage of
neonatal foals and rapidly estimate possible systemic disorders. For further expanding the applicability of RPR in neonatal foals, multicenter longitudinal studies with a larger
number of healthy and critically ill neonates are necessary.