This document provides guidance for general practitioners on interpreting common routine laboratory investigations. It discusses the importance of laboratory tests in confirming clinical diagnoses and guidelines treatment while supplementing, not replacing, clinical examination. The key laboratory tests a general practitioner should be familiar with interpreting are described in detail, including complete blood count, blood sugars, urine analysis, renal and liver function tests. Normal ranges are provided and abnormal results are interpreted for each test to guide practitioners in reaching the right diagnosis.

1. Interpretation of
Routine Laboratory
Investigations
in
General Practice
Dr.Jithesh.K,MD (General Medicine)
Senior Consultant Physician
STARCARE HOSPITAL,KOZHIKODE

2. We were taughtand
there areevidences,
which show thatagood
CaseHistoryanda
thoroughClinical
examination usually
reveals most,ifnotallof
clinically relevant data.
BUT…..
 There remains a need to confirm/document our clinical
impression though, due to present trends of EBM and the
Medico-Legal environment.
 Lab investigations supplement rather than replace other methods
for gathering information.
 It is a known fact that with the help of lab investigations, some
underlying systemic conditions of which the patients(or even
doctors) are unaware of, are often identified in General practice
for the first time.

3. Is there a
ROUTINE for
Laboratory
investigations
in all patients ?
NO,
BUT THE LAB TEST YOU SELECT IN YOUR
CLINICALPRACTICE SHOULD HELPTO…
 Confirm or reject your clinical diagnosis.
 Provide suitable guidelines in your patient management.
 Provide prognostic information of the diseases under your
consideration.
 Detect diseases through case-finding screening methods.
 Establish normal baseline values before treatment.
 Monitor follow up therapy.
 Provide information for Medico-Legal consultations.

4. On what basis
should I select
my Routine lab
investigations
in myGeneral
practice?
Accuracy
Cost effectiveness
Interfering factors
Morbidity
Reference Range
Specimen collection
Sensitivity
Specificity
SENSITIVITY
(SCREENING)
The probability that a patient
with disease has positive test
SPECIFICITY
(DIAGNOSTIC)
The probability that a healthy
patient has a negative test

5. Is Blood routine
examination and
Urine routine
examinationa
ROUTINE
laboratory
investigation?
NO
• Hb
• RBC
• TC
• DC
• PLATELETCOUNT
Blood routine
examination is better
called Complete blood
count(CBC).
• Urine macroscopy
• Urine microscopy
• Urine chemical
tests
Urine routine
examination is better
called urine analaysis.

6. What are the
Routine
Laboratory
investigations
used by a
General
Practitioner that
are going to be
discussed here ?
Primary discussion
Complete Blood Count(CBC)
ESR
Blood Sugars
Urine analysis
Renal FunctionTests(RFTs)
Liver FunctionTests(LFTs)
Addendums
Peripheral smear
CRP
HBA1C
Uric acid
Prothrombin time

7. Why ?
Correct
interpretation
of these routine
laboratory
investigations
usually directs
the General
practitioner to
the right
diagnosis in
daily practice!!
RIGHT DIAGNOSIS

8. COMPLETE
BLOOD
COUNTS (CBC)
or HEMOGRAM
+
PERIPHERAL
SMEAR
(Treasuretrovefordiagnosis
ofsomanyHematological
andNonhematological
diseases)
Hemoglobin(Hb)
RBC counts
Total WBC counts(TC)
DifferentialWBC counts(DC)
Platelet counts(Plt)
Hematocrit(PCV, Packed cell volume)
Mean corpuscular volume(MCV)
Mean Corpuscular Hemoglobin(MCH)
Mean Corpuscular Hemoglobin concentration(MCHC)

9. COMPLETE
BLOOD
COUNT (CBC)
NormalValues

10. HEMOGLOBIN
(12-15gm/dl)
IF LOW HEMOGLOBIN
(ANAEMIA)
MCV
LOW (MICROCYTIC)(<85fl)
NORMAL
(NORMOCYTIC)(85-100fl)
HIGH
(MACROCYTIC)(>100fl)
IF HIGH HEMOGLOBIN
(POLYCYTHAEMIA)
ERYTHROPOETIN
LOW (POLYCYTHAEMIA-
VERA)
HIGH(SECONDARY
POLYCYTHAEMIA)

11. CAUSESOF
ANAEMIA
BASEDON
MCV

12. CAUSESOF
POLYCYTHAEMIA
(PCV/HEMATOCRIT>55%)
NORMAL
ERYTHROPOEITIN

13. TotalWBC count
(TC)
(5,000-10,000/mm3)
>10,000/mm3 <5,000/mm3

14. Differential
count (DC)
Neutrophils(60-
70%) or (3000-
7000/mm3)
Lymphocytes(20-
30%) or (1000-
4000/mm3)
Eosinophils(1-
3%) or (50-
400/mm3)
Basophils (0.3-
0.5%)and
Monocytes(3-
8%)

15. Interpretation
of the
Neutrophil
count

16. Interpretation
of Neutrophil
count

17. Interpretation
of
Lymphocytic
count
The ALC can then be calculated by multiplying the
WBC and the percentage of lymphocytes:
ALC (cells/microL) = WBC (cells/microL) x percent
lymphocytes ÷ 100
Reactive/clonal/malignant — Lymphocytosis can
be either a reactive polyclonal proliferation or a
clonal expansion.

18. Causes of
Lymphocytosis
Reactive
Acute viral infections
(e.g., hepatitis, chicken
pox, cytomegalovirus
(CMV), Epstein-Barr virus
(EBV), herpes, rubella)
Certain bacterial infections
(e.g., Enteric fever,
pertussis (whooping
cough), tuberculosis (TB))
Clonal
Acute/Chronic
Lymphocytic
Leukemias
Lymphomas

19. Causes of
Lymphocytop
-enia
Autoimmune disorders (e.g., lupus,
rheumatoid arthritis)
Infections (e.g., HIV,TB, hepatitis, influenza)
Bone marrow damage (e.g., chemotherapy,
radiation therapy)
Immune deficiency

20. Interpreting
Eosinophil,Mo
nocyte and
Basophil
counts

21. Interpretation
of Platelet
counts
Thrombocytopenia
-<1lakh/mm3
Thrombocytosis-
>4.5Lakhs/mm3

22. Interpretation
of ESR

23. ESR vsCRP

24. Interpretation
of Blood
sugars
GLUCOMETER
(LESS RELIABLE/EMERGENCIES/HOME
USE)
GLUCOSE OXIDASE METHOD
MANUAL/AUTOANALYS
ER)
(LABORATORY/DEPENDABLE/TAKESTIME)

25. Interpretation
of Blood sugar
levels
HYPERGLYCAEMIA /
DIABETES MELLITUS
HYPOGLYCAEMIA
MILD
HYPOGLYCA
EMIA-
<70mg/dl
SEVERE
HYPOGLYC
AEMIA-
<45mg/dl

26. Causes of
Glucose level
variations
Hyperglycaemia
Diabetes Mellitus
Drugs(eg Steroids)
IV fluids
Infections
Stress
Pancreatitis
Hypoglycaemia
Starvation
OHAs/Insulin overdose
Alcohol
CKD
Liver diseases
Malignancy
Hypothyrodism
Infections

27. Interpretation
of Renal
function
tests(RFTs)
Urine Analysis
Blood urea
Serum creatinine
Serum uric acid
GFR(wont be discussed here)
Tubular function test (Wont be discussed
here)
Cystatin C (Novel marker,wont be discussed
here)

28. UrineAnalysis
Color- Pale yellow Normally, Cloudy
appearance suggest infection

29. UrineAnalysis

30. UrineAnalysis

31. UrineAnalysis

32. UrineAnalysis

33. UrineAnalysis

34. UrineAnalysis

35. UrineAnalysis

36. UrineAnalysis

37. RFTs

38. RFTs

39. RFTs

40. RFTs

41. RFTs

42. RFTs

43. RFTs

44. Interpreting
LFTs
Bilirubin:
• Total Bilirubin
• Direct Bilirubin (conjugated bilirubin)
Serum aminotransferases
• Aspartate aminotransferase (AST/SGOT)
• Alanine aminotransferase (ALT/SGPT)
Total Proteins
Albumin
Globulin
A/G Ratio
Alkaline Phosphatase
Prothrombin time

45. TOTAL
BILIRUBIN
(REPORTED
IN LFT)
Used to determine liver’s ability to clear
endogenous/exogenous substances from the circulation
Derived mainly from hemoglobin (95%)
Continuous production (300 mg daily)
Normal values of “Total” bilirubin = 0.1-1.0 mg/dL
Jaundice usually develops with a bilirubin ≥ 3 mg/dL

46. SUBTYPESOF
BILIRUBIN
DIRECT BILIRUBIN
Reported in LFT
0.0-0.2mg%
Conjugated hyperbilirubinaemia >15%
T.Bilirubin
Rarely exceeds >6mg% in the absence of
renal dysfunction
Conjugated
Water soluble
Polar
Seen in urine
Elevated with biliary obstruction and
hepatocellular disease.
INDIRECT BILIRUBIN
CALCULATED
Total Bilirubin- Conjugated bilirubin
If >85% of total bilirubin-Unconjugated
hyperbilirubinemia
Lipid soluble/Water insoluble
Non-polar
Not in urine
Elevated with Gilberts syndrome,hemolysis,
hepatic disease

47. LIVER
ENZYMES
or
AMINOTRANS
FERASES
Hepatic enzymes that are usually intracellular, but are
released from hepatocytes with hepatocellular injury.
Catalyze -amino group transfers
• aspartate or alanine  ketoglutarate
AST/ALT ratio
• Normal is 0.8
• In alcoholic hepatitis, is usually > 2

48. Liver Enzymes
or
Aminotransfer
ases
 Elevated in nearly all liver diseases (ALT > AST)
 Markedly  usually in hepatocellular disease
 Levels may/may not reflect extent of damage
 Do not correlate with eventual outcome
 Usually <500 in obstructive jaundice
Exception: acute phase of biliary obstruction by the
passage of a gallstone into the common bile duct. In
this, the aminotransferases can briefly be in the 1000–
2000 IU/L range. However, levels decrease quickly, and
the LFT rapidly evolve into typical of cholestasis
 Usually parallel each other
 AST > ALT with EtOH, fulminant, and pregnancy

49. AMINOTRANS
FERASES
Aspartate
aminotransferase
(AST/SGOT)
 In cytosol and
mitochondria
 Liver > heart >
skeletal muscle
> kidneys >
brain > pancreas
> lungs > WBCs
> RBCs
 Half-life 17hrs
Alanine
aminotransferase
(ALT/SGPT)
 In cytosol
 Predominantly
liver
 More sensitive
and specific
than AST
 Half-life
47hrs

50. Liver Enzymes
 Acute hepatocellular disorders
ALT is higher than or equal to the AST.
 C/c viral hepatitis and NAFLD
AST:ALT ratio is typically <1 (but as cirrhosis develops, this
ratio rises to >1)
 Alcoholic liver disease
AST:ALT ratio >2:1 .
The AST in alcoholic liver disease is rarely >300 IU/L, and the
ALT is often normal.
A low level of ALT in the serum is due to an alcohol-
induced deficiency of pyridoxal phosphate

51. Alkaline
Phosphatase
 Enzymes that catalyze hydrolysis of large number of
organic phosphate esters.
 ALP mainly comes from surface of bile duct epithelial cells.
Cholestasis enhances synthesis and release of ALP
 Since half life is 1week ; ALP rise late in bile obstruction and
decrease slowly after resolution
 Found in:
 Liver
 Bone
 intestine
 3rd trimester placenta
 Kidney

52. Alkaline
Phosphatase
Increases seen with cell injury or
obstruction
Slight to moderate (1-2x) – usually
hepatocellular
Large increases (3-10x) –
obstruction or cholestasis

53. Alkaline
phosphatase

54. GAMMA-
GLUTAMYL
TRANSPEPTIDA
SE (GGT)
 To confirm hepatic source of ALP
 Elevated ALP of Liver origin: Elevated GGT
Elevated ALP of Bone origin: Normal GGT
 Normal levels=0-45 IU/L
 Non specific as Causes of elevations include
Liver disease » Pancreatic
disease
Alcohol » Renal disease
Cardiac disease » Obesity
Radiotherapy » Diabetes
Drugs – GGT is “inducible”
 phenobarbital  anticoagulants
 dilantin  oral contraceptives
 acetaminophen  tricyclic antidepressants
 Usually normal in pregnancy

55. GAMMA-
GLUTAMYL
TRANSPEPTIDA
SE (GGT)

56. Prothrombin
Time (PT)
Normalrange PTis:
11to13.5seconds(Test)
INRof0.8to1.1
 Liver is in charge of the synthesis of many
clotting factors :
 Factor I (fibrinogen) , II (prothrombin)
,V ,VII , IX , X , XII and XIII
 PT measures the rate of conversion of
prothrombin to thrombin (requiring factors II,
V,VII, and X) and thus reflects a vital synthetic
function of the liver
 Elevated PT may be reflection of decreased
synthetic activity of liver.

57. Prothrombin
Time (PT)
Other causes of prolongation:
congenital deficiencies
consumptive coagulopathies (i.e.,
DIC)
drugs (i.e., warfarin)
vitamin K deficiency (i.e., dietary,
 bile output)

58. Prothrombin
Time (PT)