Serum Creatinine Elevations in Newborn Foals
Thomas J. Divers • Alexandra J. Burton • Lisa E. Fultz
During the first 1 to 3 days of life, the serum creatinine concentration in foals is often 30% to 40% higher than in their dams.94 The cause is unclear but likely related to an inability of creatinine to equilibrate rapidly across placental membranes.
As supportive evidence, creatinine concentration of normal amniotic fluid (which contains fetal urine) at term is approximately 10 mg/dL (and may be >30 mg/dL in some mares).95 The term “spurious hypercreatinemia” is used to describe the condition in foals that have truly increased serum creatinine levels but no other markers of renal injury (e.g., normal urinalysis, electrolyte and BUN concentrations). The increased creatinine is often related to placental dysfunction during gestation and can occasionally exceed 20 mg/dL in premature foals. In one study, 20/28 foals with spurious hypercreatinemia had a clinical diagnosis of neonatal encephalopathy (neonatal maladjustment syndrome).96 The association between neonatal encephalopathy and hypercreatinemia is unclear. Surprisingly few foals were from mares with documented placental pathology in one study, but these foals often had evidence of periparturient stress including premature placental separation or dystocia.96Therefore, when elevated creatinine is detected in an otherwise healthy foal (that has also been observed to urinate normally), there may be no cause for alarm, but if levels do not decline rapidly after birth (or remain >2.5 mg/dL on day
3 of life), peritoneal or retroperitoneal accumulation of urine, renal hypoplasia, or other causes of renal failure should be considered. Unlike creatinine, serum BUN values in foals are typically low (azotemia.101 In one case series, 15.9% of foals with severe hyponatremia displayed signs of encephalopathy, likely related to cerebral edema and increased intracranial pressure.99 Sodium-losing nephropathy with ARF has been confirmed in some cases.101 In azotemic foals, hyponatremia due to ARF is often related to confirmed or suspected neonatal sepsis.101 One study found no difference in the severity of hyponatremia and short-term survival rate (72.5%).99 Azotemic foals experiencing hyponatraemic encephaolopathy typically respond well to IV fluid administration with gradual sodium replacement (0.5 mmol/h).101