Interpretation of Laboratory Data PDF

Interpretation of Laboratory Data Introduction Laboratory tests can provide useful information for clinicians for the diagnosis of a medical condition and for the monitoring of drug therapy (e.g., effect of an antibiotic therapy for a bacterial infection). As a pharmacist, labor...

Interpretation of Laboratory Data Introduction Laboratory tests can provide useful information for clinicians for the diagnosis of a medical condition and for the monitoring of drug therapy (e.g., effect of an antibiotic therapy for a bacterial infection). As a pharmacist, laboratory values can help select the most safe and appropriate therapy for patients, in addition to aid in the monitoring of the selected therapy. A) Electrolytes Electrolytes and blood chemistries are important for maintaining acid-base and fluid balance. They also play a vital role in nerve and muscle functioning. These usually comprise of 1. Sodium 2. Potassium 3. Chloride 4. Calcium 5. Magnesium 6. Phosphate. 1) Sodium Sodium is the most prevalent extracellular cation in the body. Its primary function is to regulate the serum osmolality, fluid balance, and acid-base balance. Measuring serum sodium values helps in assessing the patient’s electrolyte, water, and Acid-base balance. It also helps assess their renal function. Normal values: 135-145 mEq/L. Hyponatremia Serum sodium of less than 135 mEq/L Causes of hyponatremia may be 1. Replacement of lost solute with water a. Loss of solute (e.g., vomiting, diarrhea) usually involves the loss of isotonic fluid; therefore, alone, it will not cause hyponatremia. b. After the loss of isotonic fluid, hyponatremia can develop when the lost fluid is replaced with water. c. A common cause of hyponatremia in hospitals is the postoperative administration of hypotonic fluid. 2. Edema from a relative increase in free body water. 3. Certain drugs, like tricyclic antidepressants, loop and thiazide diuretics and antiepileptic drugs (e.g., carbamazepine, oxcarbazepine). Hypernatremia Serum sodium of >145 mEq/L Often occurs as a result of dehydration or fluid loss, which could be due to conditions such as gastroenteritis, diarrhea, or Cushing’s syndrome. 2) Potassium Potassium is the main intracellular cation and plays a key role in many bodily functions including nerve excitability acid-base balance, and muscle function. Normal values: 3.5-5 mEq/L. Hypokalemia K+ concentration < 3.5 mEq/L Causes of hypokalemia include 1. Severe diarrhea 2. Alkalosis 3. Loop and thiazide diuretics 4. Insulin 5. Β-agonist (e.g., Albuterol, dobutamine) 6. Osmotic diuretics, like mannitol. Hyperkalemia K+ concentration >5 mEq/L Causes of hyperkalemia include 1. Acidosis 2. Renal failure 3. Certain drugs, like angiotensin converting enzyme inhibitors (ACEIs) 4. Potassium sparing diuretics Ex: Spironolactone 3) Chloride Chloride is the principal extracellular anion which functions to serve a passive role in the maintenance of fluid balance and acid-base balance, by having an inverse relationship with bicarbonate. Normal values: 96 -106 mEq/L. Any deviations in normal values are a sign of fluid or acid-base balance disorder, such as metabolic acidosis, respiratory alkalosis, or prolonged vomiting. 4) Calcium Normal serum 8.5 - 10.5 mg/dL (includes ionized calcium and calcium bound to protein, primarily albumin, and ions) Ionized calcium: 4.4-5.3 mg/dL Ionized calcium is more accurate, especially in patients with hypoalbuminemia; evaluate before repleting Ca2+ Hypocalcemia Serum calcium 5.3 mg/dL Causes of hypercalcemia 1. Hyperparathyroidism 2. Some malignancies, especially breast, lung, kidney; multiple myeloma, leukemia, lymphoma 3. Medications: thiazide diuretics, lithium, vitamin A toxicity 4. Immobilization 5. Hyperthyroidism Corrected Ca (mg/dL) = (0.8 x (4 – plasma albumin in g/dL)) + Serum Calcium.  5) Phosphorus Major intracellular anion; 85% of body stores found in bone Reference range: 2.5 ‐ 4.5 mg/dL Function 1. Muscle function 2. Bone formation 3. Cell membrane composition 4. Nerve conduction 5. Metabolism, adenosine triphosphate (ATP) production Hypophosphatemia Serum phosphate < 2.5 mg/dL Etiology 1. Impaired absorption (diarrhea, Vitamin D deficiency, impaired metabolism) 2. Medications: phosphate binding antacids, sucralfate, insulin, steroids 3. Alcoholism, especially during withdrawal 4. Intracellular shifts in alkalosis, anabolism, neoplasms 5. Refeeding syndrome 6. Increased losses: hyperparathyroidism, renal tubular defects and hypomagnesemia Hyperphosphatemia Hyperphosphatemia (>4.5 mg/dL) Causes of hyperphosphatemia 1. Decreased renal excretion: acute or chronic renal failure (GFR