Interpreting Laboratory Tests
LAB TESTS
1. Why?
• To aid diagnosis
• To monitor progress
• To determine corre ct dosage
2. Relationship to pharmacy
• Altered dose in ren al failure, liver fa ilure, e.g., digoxin.
• Drugs may affect lab test results, e.g., urine glucose tests.
• Monitoring serum drug levels, e.g., tobramycin pre and post levels.
• Monitoring results of treatment, e.g., effect of antibiotic therapy on WBC in bacterial infection
3. “Normal”
• Statistical normal, e.g., gaussian curve
• Depends on equipm ent and method used; thus may vary between different labs. Use the “normal
values” table for appropriate lab.
• Test may be inaccurate, e.g., hemolyzed RBC and po tassium level, failure to refrigerate urine
specimens, inaccura te timing - drug post levels.
• Important to interpret for the patien t and disease states involved, e.g. , calcium level with
hypoproteinemia.
TREAT THE PATIENT, NOT THE L AB DATA.
4. Example of orders that might be wr itten when a patient is admitted to hospital:
• Admit
• AAT, DAT
• Vital signs, routine
• CBC + diff, platelets, morphology
• PT/PTT, B12, folate, T4
• Lytes, BUN, CR, Ca, PO5, Mg
• AST, LDH, amylase, alk phos, bilirubin (T+D)
• Serum protein electrophoresis
• Fasting blood glucose, T/G, cholesterol
• MSU for C&S
• 24-hour urine collection for protein and creatinine
ELECTROLYTES
1. Three fluid compartments in the body:
• Intravascular - insid e RBC plus in serum
• Interstitial fluid
• Intracellular extrav ascular
• Usually it is the serum concentration that is measured which usually reflects the concentration in the
other compartments, but not always.
• Concentration depends on water pr esent.
2. Most common measurements:
• Sodium
• Major extracellular cation
• Hyponatremia - oft en due to edema = relative incre ase in free body water
Hypernatremia - often due to dehydration
