Moonlight Medicine

Adrian Paul J Rabe, MD, DPCP

Laboratory Interpretation

Laboratory Interpretation

• Supplements the history and physical examination

• Objective evidence of disease/health

Laboratory Interpretation

• Complete blood count• Bleeding tests– PT/PTT, Bleeding time

• Blood chemistry– Electrolytes (Na, K, Ca, Mg)– BUN and Creatinine– Liver enzymes (AST, ALT) and bilirubins

• Urinalysis• Arterial Blood Gas

CBC

Complete Blood count

• Hemoglobin and Hematocrit– High hemoglobin: Erythrocytosis– High hematocrit: Dehydration

(hemoconcentration) or erythrocytosis– Low hemoglobin/hematocrit: anemia

Complete Blood count

• Hemoglobin and Hematocrit–MCV – size of the RBC (“-cytic”)–MCH – amount of hemoglobin in the RBC

(“-chromic”)–MCHC – concentration of hemoglobin the

RBC– RDW – distribution of cell sizes

Complete Blood count

• Hemoglobin and Hematocrit– Microcytic Hypochromic (ITIM)

• Iron deficiency anemia or chronic blood loss• Anemia of chronic inflammation• Thalassemia• Myelodysplasia

– Normocytic Normochromic• Early stages of microcytic, hypochromic disease• Acute blood loss• Hemolytic Anemia

– Megaloblastic• Folate or Vitamin B12 deficiency

Complete Blood count

• Hemoglobin and Hematocrit– Transfusion changes• For every unit of packed RBC, increase in 10

g/L• Start of equilibration: 6 hours post transfusion• Full equilibration: 72 hours post transfusion

Complete Blood count

• WBC– Neutrophils and stabs• Elevated: Bacterial or early viral Infection,

Stress, Inflammation• Low: Neutropenia• Absolute neutrophil count (ANC) = WBC x

(Neutrophils in %) x 1000

– Lymphocytes • Elevated: viral/fungal/mycobacterial infection• Low: Lymphopenia• Absolute lymphocyte count (ALC) = same as

ANC

Complete Blood count

• Platelets– Very evanescent– Low platelets: Consumption, Viral

infection– Hard to predict platelet count after

transfusion– Adults: never transfuse less than 4 units• Coats the tubing• A Repeat platelet count should be taken

immediately up to 2 hours post transfusion

Bleeding Tests

Laboratory Interpretation

• PT/PTT– Prothrombin time: Measures the extrinsic pathway

(1572 = Factors 1, 10, 5, 7 and 2)• Liver disease: poor production of factor VII• Warfarin

– Partial thromboplastin time: Measures the intrinsic pathway• Heparin• APAS• Coagulation factor deficiency (hemophilia)

– Both prolonged• DIC• End-stage liver disease• Warfarin

Laboratory Interpretation

• Bleeding Time– Does not predict bleeding risk even in

surgery– No longer recommended

Blood Chemistry

BUN and Creatinine

• BUN – produced by the body and converted through the urea cycle– Increased BUN: Increased production– GI bleed

• Creatinine – produced by the muscles, excreted by the kidney with little tubular reabsorption– Increased Creatinine: Increased

production or decreased clearance

BUN and Creatinine

• BCR = BUN:Creatinine ratio– BUN/Creatinine in mmol x 247– If > 20 = pre-renal– If 10-15 = intrinsic renal

• Replaced by the Fractional excretion of sodium (FENa)– (UNaPCr)/(PNaUCr)

– If < 1% = pre-renal– If > 2% = intrinsic renal failure

BUN and Creatinine

• Creatinine Clearance = GFR– (140-age) x weight x 88.4 (x 0.85 if

female)72 x Plasma creatinine

– Estimates amount of creatinine filtered

Sodium (Na)

• Correlated with body water• Sodium is normally present in

equimolar amounts• Water diffuses through

semipermeable compartments to equilibrate

Sodium (Na)

• Total body water–% body water x kg body weight–Males: 60%– Females and Elderly (Age > 60): 50%

• Plasma osmolality– 2(Na+K) + BUN + RBS in mmol/L– BUN/2.8 if in mg/dL– RBS/18 if in mg/dL– Normal: 275-290 mmol/L

Sodium (Na)

• Total body water– 50 kg male?– 70 kg female?

• Plasma osmolality– Na 135, K 3.5, BUN 8, RBS 5– Na 125, K 4.0, BUN 10, RBS 8

Sodium (Na)

• Hyponatremia– Check Plasma osmolality– High osmolality• Hyperglycemia• Mannitol

– Normal osmolality• Hyperlipidemia/proteinemia• Bladder irrigation

– Low osmolality• Check Urine output

Sodium (Na)

• Hyponatremia (Low osmolality)–Maximal urine output• Primary polydipsia (patient drinks a lot,

diluting Na)• Pituitary problem/fever

– Poor urine output• Check ECF volume

Sodium (Na)

• Hyponatremia (Low osmolality, Poor UO)– Increased ECF volume (dilutional)

• Heart failure• Liver failure• Kidney failure/nephrotic syndrome

– Normal ECF volume• SIADH• Hypothyroidism• Adrenal insufficiency

– Decreased ECF volume• Loss of Na (renal, sweat, diuretics)

Sodium (Na)

• Hypernatremia– Check ECF volume– High ECF volume• Use of hypertonic solutions

– Low ECF volume• Check Urine output

Sodium (Na)

• Hypernatremia (Low ECF volume)–Minimal urine output• Free water losses/Dehydration

– Good urine output• Check urine osmolality• 24 hour urine TV, Na, K, Crea

Sodium (Na)

• Hypernatremia (Low ECF volume, Good UO)– Urine osmolality > 750• Diuresis

– Urine osmolality < 750• Diabetes insipidus• Central vs Nephrogenic (through response to

DDAVP)

Sodium (Na): Correction

• Hyponatremia– Increased ECF, no HypoNa symptoms• Used isotonic solutions• Restrict fluid to less than urine output• Loop diuretics

– Normal ECF, no HypoNa symptoms• Restrict fluid

– Low ECF or with HypoNa symptoms• Correct!

Sodium (Na): Correction

• Hyponatremia Correction– No more than 10-12 mmol/day (0.5

mEqs/hour)–Na deficit = TBW x (Desired-Actual Na)– Calculate sodium deficit of 10-12 mmol/day

• E.g. Na 100 in a 50 kg female• Desired sodium should be 110-112• TBW = 50 x 50%= 25 L• Na def = 25 x 12 = 300 mmol in 24h• 0.9% pNSS 1L x 12h

5% NaCl 855

3% NaCl 513

0.9% NaCl 154

0.45% NaCl 77

0.2% NaCl 34

Plain LR 130

D5W 0

Sodium (Na): Correction

• Hypernatremia– Stop ongoing water losses– Should correct dehydration– Oral correction is the safest– No more than 10-12 mmol per day

(0.5mmol/hr)

Sodium (Na): Correction• Hypernatremia Correction– Water deficit = TBW x [(Actual-140)/140]– Change in serum Na = (infusate Na – serum

Na)(TBW+1)

– Amount of infusate = 10 or 12/Change in serum Na• E.g. Na 160 in a 50 kg female• TBW = 50 x 50%= 25 L• Water deficit = 25L x [(160-140)/140]

= 3.57 L• Change in serum Na = (77-160)/(25+1)

= -3.19 mmol for every liter of 0.45% NaCl

• Amount of 0.45% NaCl = 12/3.19 = 3-4 L per day• 0.45 NaCl 1L x 6-8h

0.9% NaCl 154

0.45% NaCl 77

0.2% NaCl 34

Plain LR 130

D5W 0

Sodium (Na): Correction• 60 kg 23 year-old female with

diarrhea and vomiting presents with new-onset seizure– BP 90/60, HR 110, RR 24, Febrile to

touch– BUN 12, Crea 127, Na 150, K 3.5• Creatinine Clearance• Plasma Osmolality• Total Body Water• H20/Na Deficit• Plain LR is available

– Change in Na per liter– Order

0.9% NaCl 154

0.45% NaCl 77

0.2% NaCl 34

Plain LR 130

D5W 0

• 57• 311• 30 L• 2 L

• -0.65mmol/L• 15 L of plain LR • 1L per hour for 4

hours

Sodium (Na): Correction• 50 kg 40 year-old male diabetic

with decreased sensorium– BP 140/80, HR 90, RR 28, afebrile– BUN 8, Crea 150, Na 115, K 3.5, Cl 90• Creatinine Clearance• Plasma Osmolality• Total Body Water• H20/Na Deficit• Daily Na correction• Plain LR is available

0.9% NaCl 154

0.45% NaCl 77

0.2% NaCl 34

Plain LR 130

D5W 0

• 40• 239• 30 L• 750 mEqs• 360 mEqs• Plain LR 1L x 115

cc/hr

Potassium (K)

• Hypokalemia (<3.5 mmol/L)– 24h urine K and ABG– Urine K > 15 mmol/d• Acidotic = lower GI losses• Alkalotic = vomiting, sweat/renal losses,

diuresis

– Urine K < 15 mmol/d• Acidotic = DKA, RTA• Alkalotic = vomiting, Bartter’s/Liddle’s,

HypoMg

Potassium (K): Correction

• Hypokalemia Correction– Concentration• 60 mEqs via central line• 40 mEqs via peripheral line

– Rate• ≤ 20 mmol/h unless with paralysis, malignant

ventricular arrhythmias

– Amount• Every 1mmol/L decrease = 200-400 mmol

deficit• pNSS is the ideal medium

Potassium (K): Correction

• Hypokalemia Correction– 19 year-old male comes in for progressive

lower extremity weakness– K 2.7– Deficit?– Correction via peripheral line?

• 160 to 320 mEqs• pNSS 1L + 40

mEqs KCl x 6 hours, both arms

Potassium (K)

• Hyperkalemia (>5.0 mmol/L)– Failure of excretion• Intrinsic Renal problem• Drug-induced (spironolactone, K-sparing

diuretics)• Iatrogenic (overcorrection)

– Intake of massive amounts

Potassium (K): Correction

• Hyperkalemia Correction– Calcium gluconate (10% solution) over 2-3

minutes– NaHCO3 push– Glucose (G-I) solution = 10 u regular

insulin + 1 vial D50-50– Beta-agonists (salbutamol)– Diuretics (Furosemide)– Dialysis

Calcium (Ca) and Albumin

• Corrected Calcium– (40-actual albumin) x 0.02 + Actual

calcium– Do for both increased and decreased

calcium

Calcium (Ca) and Albumin

• Hypocalcemia Correction– Chronic

• Calcium Carbonate best taken with food (acid soluble)

• Calcium citrate can be taken anytime• <600 mg of calcium per dose• Age 19-50: 1000 mg/day• Age 51 and older: 1200 mg/day

– Acute, symptomatic• Calcium gluconate 10 mL of a 10% solution diluted

in D50-50 or 0.9% saline over 5 minutes• Calcium gluconate drip 10 ampules or 900 mg in 1L

of D5 or 0.9% saline over 24 hours

Calcium (Ca) and Albumin

• Hypercalcemia Correction– Volume expansion (4-6 L of 0.9% saline in

first 24 hours) until normal volume status is restored

– Loop diuretics (Furosemide)– Bisphosphonates• Zoledronic Acid 4 mg IV over 30 minutes• Pamidronate 60-90 mg IV over 2-4 hours• Onset of action is 1-3 days

– Dialysis

Magnesium (Mg)

• Part of the inseparable trio (K, Ca, Mg)

• Hypomagnesemia needs to be corrected to facilitate correction of other electrolytes

• 1g Mg = increase in 0.1 mmol/L– Target 1.0 mmol/L in Cardiac patients– Target 0.8 mmol/L in Renal patients– E.g. post-MI patient with Mg 0.6 mmol/L• MgSO4 4g in D5W 250 cc x 24h

Liver enzymes and bilirubins

• Prothrombin time• Albumin• TB, DB, IB– Elevated DB = Cholestatic– Elevated IB = Hemolytic– Both could be elevated in liver failure

• AST and ALT– NOT liver function test– Help estimate amount of liver parenchymal

damage– Hundreds to Thousands: Toxic, Viral, Ischemic– AST: ALT ratio > 2:1, likely alcoholic

Lipid profile

• Total Cholesterol (>200 mg/dL)– Statin

• HDL (<40 mg/dL in males, < 50 mg/dL in females)– Nicotinic Acid– Statin

• LDL (> 150 mg/dL)– Statin

• Triglycerides (> 150 mg/dL)– Fibrate (fenofibrate)– Statin

Urinalysis

Urinalysis

• pH• Specific gravity• Albumin• Glucose• WBC• RBC• Casts• Crystals• Epithelials

Urinalysis

• pH– Important in drug excretion– E.g. Methamphetamines eliminated with

acidic pH

• Specific gravity– If ≤1.010: hydrated vs inability to

concentrate– If ≥ 1.020: dehydrated vs compensation by

concentration

• Albumin• Glucose

Urinalysis

• Albumin– Related to the integrity of the basement

membrane– Albuminuria: infection, nephrotic

syndrome/kidney disease

• Glucose– Non-specific–May be elevated in diabetes

Urinalysis

• Epithelials– Used to gauge urine catch– If < 5: “clean catch”

• WBC– If > 5: infection in the presence of a clean

catch

• RBC– If > 5: suspect kidney injury (hematuria?

Nephritis? Infection?)

Urinalysis

• Casts–WBC casts: pyelonephritis or allergic

interstitial nephritis– RBC casts: hematuria– Broad casts: chronic kidney disease

• Crystals– Very non-specific– Even “uric acid crystals” are seen in

normal patients

Arterial Blood Gas

Arterial Blood Gas

• pH – reflects primary defect

• pCO2– Elevated: decreased ventilation of CO2– Decreased: increased ventilation of CO2

• pO2– Elevated: too high FiO2, hemoglobin

abnormality– Decreased: Poor oxygenation, or oxygen

binding

Arterial Blood Gas

• HCO3– Elevated: Alkaline– Decreased: Acidic

• O2 saturation– If >90%: regular pulse oximeter cannot

reliable distinguish frequencies

ABG Interpretation

• Identify adequate oxygenation and saturation– Oxygenation: enough oxygen in the blood

(pO2)– Saturation: enough oxygen bound to RBCs

(O2 Sat)

ABG Interpretation

• Identify Acid-Base problem:– Acidosis or Alkalosis?– Choose between pCO2 and HCO3• Acidosis: increased pCO2 OR decreased HCO3• Alkalosis: decreased pCO2 OR increased HCO3

– Establish predominant pathology• (pCO2 – 40)/40• (HCO3-24)/24• Biggest absolute value is the predominant

pathology

ABG Interpretation

• Identify Acid-Base problem:– Determine if primary problem is

compensated• (pCO2 – 40)/40• (HCO3-24)/24• Biggest absolute value is the predominant

pathology

ABG Interpretation• Identify Acid-Base problem:

Predominant pathology CompensationMetabolic Acidosis

(Low HCO3)For every mmol decrease in

HCO3, pCO2 decreases by 1.25Metabolic Alkalosis

(High HCO3)For every mmol increase in

HCO3, pCO2 increases by 0.75

Respiratory Acidosis(High pCO2)

AcuteFor every mmol increase in

pCO2, HCO3 increases by 0.1Chronic

For every mmol increase in pCO2, HCO3 increases by 0.4

Respiratory Alkalosis(Low pCO2)

AcuteFor every mmol decrease in

pCO2, HCO3 decreases by 0.2Chronic

For every mmol decrease in pCO2, HCO3 decreases by 0.4

ABG Interpretation

• If there is metabolic acidosis– Take anion gap• (Na + K) – (Cl + HCO3)• Normal is 10 to 12

– HAGMA: MUDPILES• Methanol, uremia, DKA, Propylene

glycol/Paraldehyde, Isoniazid/Iron, Lactic Acid, Ethanol/Ethylene glycol, Sulfates/Salicylates

– NAGMA: STRaND• Spironolactone, TPN, RTA, Na-containing

solutions, Diarrhea

ABG Interpretation

• If there is HAGMA– Take changes in anion gap and HCO3– Δ AG > Δ HCO3 = HAGMA with Metabolic

alkalosis– E.g. Uremia with vomiting

• If there is NAGMA– Take changes in HCO3 and Cl– Δ AG > Δ Cl= NAGMA with HAGMA– E.g. Diarrhea and lactic acidosis,

treatment of DKA

ABG Interpretation

• 40• 239• 30 L• 750 mEqs• 360 mEqs• Plain LR 1L x 115

cc/hr

• 50 kg 40 year-old male diabetic with decreased sensorium– BP 140/80, HR 90, RR 28, afebrile– BUN 8, Crea 150, Na 115, K 3.5, Cl 90• Creatinine Clearance• Plasma Osmolality• Total Body Water• H20/Na Deficit• Daily Na correction• Plain LR is available

ABG Interpretation

– pH 7.1, pCO2 28, pO2 78, HCO3 10, O2 Sat 88%• Oxygenation /Saturation?• Acidosis or Alkalosis?• Respiratory or Metabolic?• Compensated?• Anion Gap?• Secondary problems?

• Poor; Poor• Acidosis• Metabolic• Expected pCO2 27.5;

compensated • 15 (High Anion Gap)• 3 < 14; None

• 50 kg 40 year-old male diabetic with decreased sensorium– BP 140/80, HR 90, RR 28, afebrile– BUN 8, Crea 150, Na 115, K 3.5, Cl 90