When lab results are deceiving

July 1, 2009

A teenage girl undergoes a series of lab tests, which all come back negative. The complaints turns out to be one of the negative lab results - but which one?

You have just finished rounds on your busy service at the children’s hospital, and sit down for a well-deserved cup of coffee. You receive a page from a community pediatrician seeking a pulmonary consultation for one of her patients. As you sip, she describes a 15-year-old Caucasian female with a four-week history of fatigue and chest pain.

Additional studies obtained at that time included an unremarkable electrocardiogram, electrolytes, hepatic function panel, and urinalysis. Her complete blood count (CBC) was remarkable for a total white blood cell count of 7,110/mm3 and peripheral eosinophilia (4.4%). You ask about tuberculosis testing, and her pediatrician tells you that the PPD she placed demonstrated no induration.

Fatigue, chest pain, and solitary pulmonary nodule...what to do?

You down the rest of your coffee, and recommend a thoracic CAT scan, and additional testing for immunologic and rheumatologic testing, as sarcoidosis and Wegener's granulomatosis are high on your differential. You also recommend testing for antibodies to Blastomyces dermatiditis and Histoplasma capsulatum. Finally, you arrange to see the patient in your clinic the following week.

One week later

Before the patient arrives in clinic, you pull up her laboratory results and radiology results in the electronic medical record system. Testing for blastomycosis and histoplasmosis antibodies, immunoglobulins G, A, and M, angiotensin-1-converting enzyme, and C- and P-antineutrophil cytoplasmic antibodies (ANCA) are all unremarkable. Her erythrocyte sedimentation rate is 13 mm/hr. However, her thoracic CT scan now demonstrates two nodules in the right lower lobe, one 6-x-7 mm, the other 1-x-1.1 cm.

With your hand raised to knock on the exam room door, you ponder nodules for a minute. Customarily, nodules are defined as round lesions less than three centimeters in diameter. Although up to 40% of solitary nodules may be malignant in adults, the risk of malignancy is exceedingly rare in younger patients, particularly those with no history of active smoking.1,2 The risk that a solitary nodule is malignant in patients 35 to 39 years old is only 3%, and even lower in the pediatric population.3 Studies in adults suggest that granulomatous infectious processes account for 80% of benign lesions.1

You walk into the exam room and meet the patient and her mother. The patient relates that she has intermittent chest pain on her right side. Occasionally, the pain radiates ipsilaterally to her back. You do a full review of systems. The patient reports occasional dry mouth, intermittent rhinorrhea, occasional mild headaches, and some mild blurry vision in the morning lasting for about an hour. The patient denies any recent weight loss, night sweats, fever, rashes, emesis, diarrhea, or cough.

The review of systems suggests an autoimmune diagnosis; you press on with your history.

The patient's mother notes that the patient has a history of gastroesophageal reflux disease with chronic gastritis, diagnosed by endoscopy three years ago. A colonoscopy performed at the same time demonstrated slightly greater number of eosinophils than normal on biopsy. The patient also has a history of dysmenorrhea. Additionally, the patient reports that she is taking lansoprazole and an oral contraceptive. The family denies any known drug allergies. The family history is notable for juvenile rheumatoid arthritis, systemic lupus erythematosus, and Crohn's disease. The family resides outside a major East Coast city. There has been no recent construction or excavation near the patient's residence or school. The patient has not traveled outside the US, and has not spent any time in caves, attics, old buildings, or working on a farm.