Potassium Hydroxide: An Alternative Reagent to Perform the Modified Apt Test Henry Chicaiza, MD1,2, Karl Hellstrand, DO1,2, Trudy Lerer, MS1, Sharon Smith, MD1, and Francisco Sylvester, MD1,2 We tested the performance of potassium hydroxide (KOH) in the modified Apt test under different experimental conditions using sodium hydroxide as a positive control. Like sodium hydroxide, KOH differentiated fresh fetal and adult blood stains on a cloth but not dried blood. KOH may be used to perform the Apt test at the bedside. (J Pediatr 2014;165:628-30).
H
ematemesis in any child, especially in a newborn can generate a great deal of anxiety in caregivers and healthcare providers alike. Typically, caregivers present to the primary care setting, the emergency department, or newborn nursery with a cloth containing blood tinged emesis. The most common cause of hematemesis in a newborn is swallowed maternal blood from an irritated or cracked nipple,1 followed by ingestion of mother’s blood during delivery. The healthcare provider must, therefore, be able to promptly differentiate internal bleeding from ingested maternal blood in the neonate. Otherwise, the newborn may be subject to unnecessary tests and invasive procedures such as endoscopy. The Apt test is used to distinguish blood of maternal origin from that of neonatal origin.2 The Apt test is based on the difference in reaction time between adult and fetal hemoglobin when exposed to a strong alkaline reagent.2 Studies done in the nineteenth century showed that human placental blood was resistant to alkaline denaturation compared with the blood of normal adults.3,4 In 1957, Apt designed a method that used this principle for bedside application but did not report the experimental data.2 In 1994, McRury and Barry used adult venous blood and newborn cord blood to examine the usefulness of the modified Apt test in diagnosing neonatal hematemesis secondary to ingested maternal blood.2,5 Even though they found that cord blood was resistant to denaturation by sodium hydroxide (NaOH), the study had limitations. Mainly, the blood samples were not pre-exposed to an acidic environment, which would occur when infant blood or swallowed maternal blood mixes with gastric contents prior to vomiting. Moreover, McRury and Barry used a 10% NaOH solution (pH 14.4), which because of its strong caustic properties, is not readily available at the point of care. Another alkaline solution, potassium hydroxide (KOH, pH 14.3), is more readily available and is not caustic. A 10% KOH solution is routinely used to perform the “wet prep test” in samples suspicious for fungal infections. Because NaOH and KOH have a similar pH, we hypothesized that KOH would perform equally well as
HCl KOH NaOH PEM
Hydrochloric acid Potassium hydroxide Sodium hydroxide Pediatric emergency medicine
NaOH in the modified Apt test and, therefore, would increase the feasibility of performing the Apt test at the bedside.
Methods The blood samples were left over blood from adult and newborns that had blood drawn for clinical use and were set to be discarded. Venous blood samples from adults (18-50 years old, n = 30) and newborns (
H
ematemesis in any child, especially in a newborn can generate a great deal of anxiety in caregivers and healthcare providers alike. Typically, caregivers present to the primary care setting, the emergency department, or newborn nursery with a cloth containing blood tinged emesis. The most common cause of hematemesis in a newborn is swallowed maternal blood from an irritated or cracked nipple,1 followed by ingestion of mother’s blood during delivery. The healthcare provider must, therefore, be able to promptly differentiate internal bleeding from ingested maternal blood in the neonate. Otherwise, the newborn may be subject to unnecessary tests and invasive procedures such as endoscopy. The Apt test is used to distinguish blood of maternal origin from that of neonatal origin.2 The Apt test is based on the difference in reaction time between adult and fetal hemoglobin when exposed to a strong alkaline reagent.2 Studies done in the nineteenth century showed that human placental blood was resistant to alkaline denaturation compared with the blood of normal adults.3,4 In 1957, Apt designed a method that used this principle for bedside application but did not report the experimental data.2 In 1994, McRury and Barry used adult venous blood and newborn cord blood to examine the usefulness of the modified Apt test in diagnosing neonatal hematemesis secondary to ingested maternal blood.2,5 Even though they found that cord blood was resistant to denaturation by sodium hydroxide (NaOH), the study had limitations. Mainly, the blood samples were not pre-exposed to an acidic environment, which would occur when infant blood or swallowed maternal blood mixes with gastric contents prior to vomiting. Moreover, McRury and Barry used a 10% NaOH solution (pH 14.4), which because of its strong caustic properties, is not readily available at the point of care. Another alkaline solution, potassium hydroxide (KOH, pH 14.3), is more readily available and is not caustic. A 10% KOH solution is routinely used to perform the “wet prep test” in samples suspicious for fungal infections. Because NaOH and KOH have a similar pH, we hypothesized that KOH would perform equally well as
HCl KOH NaOH PEM
Hydrochloric acid Potassium hydroxide Sodium hydroxide Pediatric emergency medicine
NaOH in the modified Apt test and, therefore, would increase the feasibility of performing the Apt test at the bedside.
Methods The blood samples were left over blood from adult and newborns that had blood drawn for clinical use and were set to be discarded. Venous blood samples from adults (18-50 years old, n = 30) and newborns (
