I remember wondering why hematology was the first
topic of clinical medicine during the didactic year of my program. Now I know
why... A complete blood cell count (CBC) has been ordered on virtually every
patient. The CBC gives you a quick inside look on a patient's energy status,
infection status, and immune status. In addition to the CBC, a basic metabolic
panel and urinalysis are the other two fundamental orders completing the lab
trifecta. Conditions like anemia, infection and UTI are fairly easy to detect based on these labs. Here are 5 tips I have
learned in the clinical setting regarding these labs that you might not know:
1. Hemoglobin
and hematocrit are often elevated in smokers because the body is trying to
churn out more RBCs in the face of chronic hypoxemia.
2. When the urine is negative for
RBCs but positive for blood, think rhabdo. Muscle wasting of rhabdomyolysis
releases myoglobin which yields positive blood but negative RBCs.
3. If the UA yields > 50
squamous cells, it is a dirty catch. Repeat the urinalysis.
4. A high BUN should raise suspicion of either a real volume depletion (most likely a GI bleed) or a perceived volume depletion. Recall a
high BUN:Crt ratio (>20:1) is indicative of pre-renal failure.
5. Pay attention to potassium in patients with suspected diabetic ketoacidosis. Levels may be normal or elevated at initial presentation because the cells are spilling K+ into the blood in favor of absorbing H+.
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