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

2. Laboratory Interpretation
Supplements the history and physical examination
Objective evidence of disease/health

3. 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

4. CBC

5. Complete Blood count Hemoglobin and Hematocrit
High hemoglobin: Erythrocytosis
High hematocrit: Dehydration (hemoconcentration) or erythrocytosis
Low hemoglobin/hematocrit: anemia

6. 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

7. 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

8. 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

9. 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

10. 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

11. Bleeding Tests

12. 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

13. Laboratory Interpretation
Bleeding Time
Does not predict bleeding risk even in surgery
No longer recommended

14. Blood Chemistry

15. 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

16. BUN and Creatinine BCR = BUN:Creatinine ratio
BUN/Creatinine in mmol x 247
If > 20 = pre-renal
If = intrinsic renal
Replaced by the Fractional excretion of sodium (FENa)
(UNaPCr)/(PNaUCr)
If < 1% = pre-renal
If > 2% = intrinsic renal failure

17. 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

18. Sodium (Na) Correlated with body water
Sodium is normally present in equimolar amounts
Water diffuses through semipermeable compartments to equilibrate

19. 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: mmol/L

20. 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

21. Sodium (Na) Hyponatremia Check Plasma osmolality High osmolality
Hyperglycemia
Mannitol
Normal osmolality
Hyperlipidemia/proteinemia
Bladder irrigation
Low osmolality
Check Urine output

22. 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

23. 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)

24. Sodium (Na) Hypernatremia Check ECF volume High ECF volume
Use of hypertonic solutions
Low ECF volume
Check Urine output

25. 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

26. Sodium (Na) Hypernatremia (Low ECF volume, Good UO)
Urine osmolality > 750
Diuresis
Urine osmolality < 750
Diabetes insipidus
Central vs Nephrogenic (through response to DDAVP)

27. 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!

28. Sodium (Na): Correction
Hyponatremia Correction
No more than mmol/day (0.5 mEqs/hour)
Na deficit = TBW x (Desired-Actual Na)
Calculate sodium deficit of mmol/day
E.g. Na 100 in a 50 kg female
Desired sodium should be
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

29. Sodium (Na): Correction
Hypernatremia
Stop ongoing water losses
Should correct dehydration
Oral correction is the safest
No more than mmol per day (0.5mmol/hr)

30. 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 [( )/140]
= 3.57 L
Change in serum Na = (77-160)/(25+1)
= 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

31. 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

32. 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

33. 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

34. 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 = mmol deficit
pNSS is the ideal medium

35. 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

36. 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

37. 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

38. Calcium (Ca) and Albumin
Corrected Calcium
(40-actual albumin) x Actual calcium
Do for both increased and decreased calcium

39. 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

40. 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 mg IV over 2-4 hours
Onset of action is 1-3 days
Dialysis

41. 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

42. 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

43. 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)

44. Urinalysis

45. Urinalysis pH Specific gravity Albumin Glucose WBC RBC Casts Crystals
Epithelials

46. 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

47. 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

48. 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?)

49. 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

50. Arterial Blood Gas

51. 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

52. Arterial Blood Gas HCO3 O2 saturation Elevated: Alkaline
Decreased: Acidic
O2 saturation
If >90%: regular pulse oximeter cannot reliable distinguish frequencies

53. ABG Interpretation Identify adequate oxygenation and saturation
Oxygenation: enough oxygen in the blood (pO2)
Saturation: enough oxygen bound to RBCs (O2 Sat)

54. 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

55. 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

56. 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

57. 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

58. 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

59. 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

60. 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