Laboratory Interpretation Moonlight Medicine Laboratory Interpretation Adrian Paul J Rabe, MD, DPCP

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 Lymphocytes 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

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 Plasma osmolality % 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 Plasma osmolality 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

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

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 57 311 30 L 2 L -0.65mmol/L 15 L of plain LR 1L per hour for 4 hours 0.9% NaCl 154 0.45% NaCl 77 0.2% NaCl 34 Plain LR 130 D5W

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 40 239 30 L 750 mEqs 360 mEqs Plain LR 1L x 115 cc/hr 0.9% NaCl 154 0.45% NaCl 77 0.2% NaCl 34 Plain LR 130 D5W

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 LDL (> 150 mg/dL) Triglycerides (> 150 mg/dL) Fibrate (fenofibrate)

Urinalysis

Urinalysis pH Specific gravity Albumin Glucose WBC RBC Casts Crystals Epithelials

Urinalysis pH Specific gravity Albumin Glucose 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 Glucose Related to the integrity of the basement membrane Albuminuria: infection, nephrotic syndrome/kidney disease Glucose Non-specific May be elevated in diabetes

Urinalysis Epithelials WBC RBC 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 Crystals 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 pCO2 pO2 reflects primary defect 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 O2 saturation 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

Predominant pathology Respiratory Alkalosis ABG Interpretation Identify Acid-Base problem: Predominant pathology Compensation Metabolic Acidosis (Low HCO3) For every mmol decrease in HCO3, pCO2 decreases by 1.25 Metabolic Alkalosis (High HCO3) For every mmol increase in HCO3, pCO2 increases by 0.75 Respiratory Acidosis (High pCO2) Acute For every mmol increase in pCO2, HCO3 increases by 0.1 Chronic For every mmol increase in pCO2, HCO3 increases by 0.4 Respiratory Alkalosis (Low pCO2) For every mmol decrease in pCO2, HCO3 decreases by 0.2 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 If there is NAGMA 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 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 40 239 30 L 750 mEqs 360 mEqs Plain LR 1L x 115 cc/hr

ABG Interpretation 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 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