Saturday, January 19, 2008

Neonatal thrombocytopenia - a puzzle

The nurse in the newborn nursery had noticed petechiae and bruising which had not been present when the baby was admitted a few hours earlier. She notified the pediatrician who transferred the baby to the NICU when he received the result of the platelet count -- 17,000, instead of the normal 150,000+ . If the count had been low, but not life-threatening, the pediatrician might have opted to repeat the test to rule out lab error or to look for a trend. 17,000 is in the range considered life-threatening, so a NICU admission during the workup isn't optional.

When the baby arrived in the NICU, she looked, aside from the petechiae and bruises, perfectly healthy. She was pink, breathing easily, and eagerly rooting. Muscle tone was excellent and she was unhappy at having to wait to be fed. All these signs are encouraging, because one of the most common causes of thrombocytopenia (abnormally low platelet count) in a term newborn, sepsis, would almost certainly result in abnormal behavior or appearance in at least one area if the baby were sick enough to have a platelet count that low. Most of the congenital syndromes which can cause severe thrombocytopenia are associated with fairly obvious characteristics and were quickly discounted. Other possible causes were considered and ruled out.

Because sepsis in a newborn can quickly be lethal, cultures were obtained and IV antibiotics started. The risk of discounting sepsis as a possibility is simply too great and far outweighs any risks of the antibiotics used.

Sepsis really wasn't near the top of the list of suspects, so blood was drawn and overnighted to a distant hospital for extensive testing to determine exactly which anti-platelet antibodies were causing the problem. The neonatologists believed that the low platelet count resulted from an incompatibility between the mother's blood and the baby's platelets. A platelet count below 20,000 in the absence of indications of sepsis is most commonly caused by Neonatal Alloimmune Syndrome.

The neonatologists suspected an alloimmune cause for the low platelet count. They considered it possible, but unlikely, that an autoimmune process was the cause, because the mother's counts were normal. IVIG - IntraVenous Immune Globulin - was given and a very brief increase (to 30,000) was achieved.

Platelet transfusions were given, to no effect. Our blood bank can "pedi-pack" (divide) platelet units in order to decrease the number of separate donors, but because the platelet count didn't rise after the first transfusion, the neonatologist requested a new unit of platelets from a different donor for each transfusion. He spoke at length with the blood bank technologists, a hematologist, and eventually the blood bank director about specific characteristics he wanted for the donors.

By the time the second platelet transfusion had had no appreciable effect, the neonatologist was convinced that we were dealing with an alloimmune incompatibility and, pending results from the distant hospital, contacted the Red Cross to have them locate donors who were most likely to match the baby while preparing to gather platelets from the mother.

One interesting observation was that the baby never had any excessive bleeding from heelsticks, IV sites, etc., and that several specimens sent for blood counts clotted before reaching the lab. A donor was located and within a very few days, the baby's platelet count rose to a safe level and she was discharged.

The lab results confirmed a diagnosis of Neonatal AlloImmune Thrombocytopenia - which occurs in 0.05-0.1% of live births - one per 1000-2000 infants. There are several antibodies associated with the condition, so finding the perfect donor is essential - and the mom may be the best choice.

According to the Institute for Transfusion Medicine (1996 numbers) mortality rate was 1-14% with first babies being most likely to be severely affected since the mom can be followed during subsequent pregnancies. 10-20% of affected babies may have intracranial bleeding with about half of bleeds occurring before birth.

Second and subsequent pregnancies can be carefully monitored. Delivery is usually elective cesarean section if the baby is affected and appropriate platelets are on hand in case the baby is symptomatic.

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