Correspondence
Clinical Problem-Solving: A Square Peg in a Round Hole
N Engl J Med 1998; 338:1926-1927June 25, 1998
- Article
To the Editor:
The Clinical Problem-Solving exercise by Saint et al. (Feb. 5 issue)1 was a useful discussion of several important topics. However, the statement that “the diagnosis of iron deficiency is virtually ruled out by the normal ferritin concentration” requires modification, since this misconception can easily lead to delay and misdiagnosis in the management of anemia.
It is well established2 that the serum ferritin concentration can be used as a reliable marker to predict iron stores in bone marrow only when an acute-phase reaction is absent. This is an important point in clinical situations such as the one described. It is equally useful to point out the converse argument — that is, that a low serum ferritin concentration implies an iron-deficient state, whatever the state of the other acute-phase proteins.3
3 ReferencesWilliam H. Whitehead, M.R.C.G.P.
Minfor Surgery, Gwynedd LL42 1PL, United Kingdom1
Saint S ,Saha S ,Tierney LM Jr . A square peg in a round hole. N Engl J Med 1998;338:379-383
Full Text | Web of Science | Medline2
Worwood M . Ferritin in human tissues and serum. Clin Haematol 1972;11:275-2753
Balaban EP ,Sheehan RG ,Demian SE ,Cox JV ,Frenkel EP . Evaluation of bone marrow iron stores in anemia associated with chronic disease: a comparative study of serum and red cell ferritin. Am J Hematol 1993;42:177-181
CrossRef | Web of Science | Medline
To the Editor:
I wish to comment on the Clinical Problem-Solving case “A Square Peg in a Round Hole.” A patient with anorexia and hyperglycemia should not be treated with metformin, certainly not as the initial treatment or the only treatment. Metformin tends to reduce food intake and can make anorexia worse. In addition, such patients may be at increased risk for lactic acidosis.
Morton Linder, M.D.
P.O. Box 629, Mt. Kisco, NY 10549To the Editor:
The management of the case described by Saint et al. left me confused. Was the delay in making the correct diagnosis really due to patterns of thinking, or were there other reasons why it took nearly six months from the appearance of the initial symptoms before a simple, relatively inexpensive, and often very helpful procedure such as standard chest radiography was performed? I wonder whether economic considerations precluded a more timely use of the test in a 51-year-old woman with a history of 30 pack-years of smoking, intermittent cough, continuing weight loss despite correction of diabetes, and a fever of unknown origin.
Charles Mahler, M.D.
General Hospital Middeheim, 2020 Antwerp, BelgiumTo the Editor:
“A Square Peg in a Round Hole” brought to mind an episode in A.J. Cronin's The Citadel. 1 The young physician, Manson, had just been interrogated by a distinguished senior physician during the oral examination to become Member of the Royal College of Physicians. The impressed examiner asked Manson, “What do you regard as the main principle — the, shall I say the basic idea — which you keep before you when you are exercising the practice of your profession?” Manson's blurted-out response — “I suppose I keep telling myself never to take anything for granted” — is the lesson taught by the case presented.
Unfortunately, there are many forces pushing us daily to jam square pegs into round holes. Time and financial pressures lead us quickly to latch onto the most parsimonious explanation for a patient's presentation, often ignoring elements that do not quite fit. Thus, an unusual diagnosis is delayed or missed entirely. To refer to a time-honored medical quotation, the hoofbeats we are hearing are occasionally caused by zebras. We owe it to our patients and to our profession not to allow our diagnostic thinking to be brought prematurely to a close by nonclinical factors.
1 ReferencesPaul A. Silver, M.D.
2141 K St., NW, Washington, DC 20037Author/Editor Response
The authors reply:
To the Editor: Dr. Whitehead takes issue with the discussant's view that the diagnosis of iron deficiency is very unlikely given the normal ferritin level. Though the performance characteristics of the measurement of serum ferritin as a diagnostic test for iron-deficiency anemia are affected by the presence of an inflammatory disease, the results of this test are still useful in these cases. Guyatt et al.1 found that the likelihood ratio associated with a serum ferritin level of 250 ng per milliliter (approximately the level in the patient under discussion) increases from 0.06 in the general population to 0.10 in those with an inflammatory condition. Thus, even if the pretest probability of iron-deficiency anemia was 50 percent in this patient, the post-test probability given this ferritin level would be approximately 9 percent. Whether a 9 percent chance of iron deficiency exceeds one's diagnostic threshold is debatable. We agree with Dr. Whitehead that the finding of a low serum ferritin level (i.e., less than 15 ng per milliliter), especially in the presence of an inflammatory disease, confirms the diagnosis of iron deficiency.1
Dr. Linder points out that metformin may have been an inappropriate initial agent in a patient with anorexia and hyperglycemia. We agree. We also concur with Dr. Mahler that economic considerations may have affected the care of this patient. Increased attention to such factors will remain important as we work under the time and financial constraints imposed by the current medical marketplace. As Dr. Silver eloquently explains, time and financial pressures should not preclude careful consideration of competing diagnoses in the case of a patient who does not have a straightforward ailment.
1 ReferencesSanjay Saint, M.D.
Somnath Saha, M.D.
University of Washington, Seattle, WA 98195-7183Lawrence M. Tierney, Jr., M.D.
University of California, San Francisco, San Francisco, CA 941431
Guyatt GH ,Oxman AD ,Ali M ,Willan A ,McIlroy W ,Patterson C . Laboratory diagnosis of iron-deficiency anemia: an overview. J Gen Intern Med 1992;7:145-153[Erratum, J Gen Intern Med 1992;7:423.]
CrossRef | Web of Science | Medline
