"Must know" labs

Question 1

Calcium (Ca)

Answer 1

total: 8.5-10.5 mg/dL
ionized: 4.5-5.1 mg/dL

• calculate corrected Ca if albumin is low.
• correction is NOT needed for ionized
• incr w/ Ca supp, vit D, thiazide diuretics
• decr. w/ long-term heparin, loop diuretics, bisphosphonates, cinacalcet, systemic steroids, calcitonin, foscarnet, topiramate
• supplement Ca in pregnancy, osteoporosis

Question 2

Magnesium (Mg)

Answer 2

1.3-2.1 mEq/L

• incr. w/ Mg-containing antacids & laxatives w/ renal impairment
• decr. w/ PPI, diuretics, amphotericin B, foscarnet, echinocandins, diarrhea, chronic alcohol intake

Question 3

Phosphate (PO4)

Answer 3

2.3-4.7 mg/dL

• incr. w/ renal failure
• decr. w/ phosphate binders, foscarnet, PO Ca intake

Question 4

Potassium (K)

Answer 4

3.5-5 mEq/L

• incr. w/ ACEi, ARBs, aldosterone receptor antagonists, aliskiren, canagliflozin, cyclosporine, tacrolium, mycophenalate, K supp, bactrim, drospirenone containing PO contraceptives, chronic heparin kus, NSAIDs, pentamidine
• decr. w/ beta-2 agonists, diuretics, insulin, steroids, conivaptan

Question 5

Sodium (Na)

Answer 5

135-145 mEq/L

• incr. w/ hypertonic saline, tolvaptan, conivaptan
• decr. w/ carbamazepine, oxcarbazepine, SSRIs, diuretics, desmopressin

Question 6

Bicarbonate (HCO3)

Answer 6

venous: 24-30 mEq/L
arterial: 22-26 mEq/L

• assess acid-base status
• incr. due to loop diuretics, systemic steroids
• decr. due to topiramate, zonisamide, salicylate overdose

Question 7

Blood Urea Nitrogen (BUN)

Answer 7

7-20 mg/dL

• incr. w/ renal impairment and dehydration
• used w/ SCr to assess fluid status and renal funct.

Question 8

Serum Creatinine (SCr)

Answer 8

0.6-1.3 mg/dL

• incr. w/ drugs that impair renal funct
• decr. w/ low muscle mass, amputation, hemodilution
• false incr. w. bactrim, H2RAs, cobicstat

Question 9

Anion Gap

Answer 9

5-12 mEq/L

elevated = metabolic acidosis

Question 10

White blood cells (WBC)

Answer 10

4K-11K cells/mm2

• used to diagnose & monitor infection/inflammation
• incr. as acute phase reactant, indicating a systemic reaction to inflammation or stress

Question 11

neutrophils

Answer 11

45-73%

determine likelihood of infection and with acute WBC in absolute neutrophil count calculation

• neutrophils = SEGmented neutrophils (“segs”)
• immature neutrophils = bands

Question 12

bands

Answer 12

3-5%

released from bone marrow to fight infection

Question 13

eosinophils

Answer 13

0-5%

incr in drug allergy, asthma, inflammation, parasitic infection

Question 14

basophils

Answer 14

0-1%

incr. in inflammation, hypersensitivity reaction, leukemia

Question 15

lymphocytes

Answer 15

20-40%

incr. in viral infections, lymphoma
decr. in bone marrow suppression, HIV, or systemic steroids

Question 16

Red Blood cells (RBC)

Answer 16

males: 4.5-5.5 x 10^6 cells/microL
females: 4.1-4.9 x 10^6

• incr. w/ erythropoiesis-stimulating agents (ESAs), smoking and polycythemia
• decr w/ chemo that targets bone marrow, low production, blood loss, deficiency anemias, hemolytic anemia, sickle cell anemia

Question 17

hemoglobin (Hgb, Hb)

Answer 17

males: 13.5-18 g/dL
females: 12-16 g/dL

• Hgb carries O2 in RBCs
• incr. w ESAs
• decr. w anemias and bleed

Coombs Test and G6PD for drug-induced anemia

Question 18

mean corpuscular volume (MCV)

Answer 18

80-100 fL

• incr. due to B12 or folate deficiency
• decr. due to Fe deficiency

Question 19

folic acid (folate)

Answer 19

5-25 mcg/L

B12 and folate are ordered for further workup for macrocytic anemia
- decr. due to phenytoin/fosphenytoin, phenobarb, primidone, MTX, bactrim, sulfasalazine

supplement folate in women of childbearing age and alcoholism

Question 20

Vitamin B12

Answer 20

> 200 pg/mL

decr. due to PPIs, metformin, colchicine, chloramphenicol

Question 21

reticulocyte count

Answer 21

0.5-2.5%

measures reticulocytes being made in the bone marrow
- reticulocyte count incr. in blood loss and decr. in untreated anemia due to iron, folate or B12 deficiency & bone marrow suppression

Question 22

Coombs Test, direct (DAT)

Answer 22

negative

diagnose hemolytic anemia, when the cause of hemolysis is unclear

• can be caused by penicillins/cephalosporins, dapsone, isoniazid, levodopa, methyldopa, methylene blue, nitrofurantoin, pegloticase, primaquine, quinidine, quinine, rasburicase, rifampin, sulfonamides

a (+) coombs test + likely drug cause: d/c drug