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A 3-year-old boy complains to his parents that his legs hurt. They reassure him that this is just growing pains but over the next few days he becomes more insistent that the pain is worse and he appears to be reluctant to walk. His mother brings him to his pediatrician™s office where the physician immediately observes that the child is pale in appearance but alert without any nausea or headache. Vital signs are temperature 38.3°C (100.9° F), blood pressure (BP) 100/65 mm Hg, heart rate 125 beats per minute and respiration rate 30 breaths per minute. There is conjuctival pallor and gingival bleeding but no papilledema or nuchal rigidity. EOMs are intact and pupils equal round and reactive to light and accommodation. The boy walks gingerly but shows no ataxia. Chest is clear and cardiac examination normal except for regular rate tachycardia. The spleen is palpable 4 cm below the costal margin. Genitalia are normal without masses. Muscle tone is normal and tendon reflexes undiminished and symmetrical. What, in addition to a complete blood count (CBC), is the most important test to order?
Blood cultures
Blood glucose levels
Fibrinogen and D-dimer levels
Serum calcium
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calcium? bone infiltration
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Option C (Fibrinogen and D-dimer levels) is correct. The child is acutely ill with a likely diagnosis of acute lymphoblastic leukemia (ALL). It is most important to determine if his platelets are critically low with a CBC and to determine if he is suffering from disseminated intravascular coagulation, which is usually screened for with fibrinogen and D-dimer levels.
Option A (Blood cultures) is incorrect. 3 sets of blood cultures should be obtained over the next 24 hours but loss of venous access during blood draws is always a consideration in any patient in an office encounter. First a diffuse intravascular coagulation (DIC) screen should be obtained. Empiric antibiotics can always be started if blood cultures cannot be obtained.
Option B (Blood glucose levels) is incorrect. It may seem that since all laboratory tests can be drawn at the same time, one need not worry which is more important. DIC screen is critical in this patient and requires a separate tube than blood glucose. Every intern knows how easily a vein can be blown during blood draws and that there may be significant delay or no success in reestablishing peripheral venous access in the office setting. DIC screening when indicated takes precedence over blood glucose levels in an alert patient.
Option D (Serum calcium) is incorrect. If the patient were showing signs of hyper or hypocalcemia this test would be among the first that should be obtained.
