PubHealth Laboratory Data Interpretation

Diabetic nephropathy sees the extracellular matrix deposited in the…

lobules of the glomeruli → damage → proteinuria

Accuracy

the agreement between the measured quantity and its true value

Accuracy is affected by __.

systemic error or bias

Precision

agreement between repetitive measurements performed in the same way

Precision is a test of __.

reproducibility

Precision is affected by __.

random error

Measuring Precision (3)

1. arithmetic mean, x

2. standard deviation, s

3. coefficient variation, CV

Measuring Precision: Arithmetic mean

average value of a set of measurements

Measuring Precision: Standard deviation

measure of the dispersion or spread of results about the mean

Standard deviation is a reflection of __.

precision

Measuring Precision: Coefficient variation

expresses the standard deviation as a percentage of the mean

Confidence intervals are used to determine whether the difference in two results can be…

accounted for solely by the imprecision of the test

Reference interval

defined by a specified proportion of the range of values in a healthy reference population

• usually 95%

The range of test values found in healthy people is determined by… (3)

1. genetic factors

2. environmental factors

3. physiologic factors

in practice the two most important factors are age and gender

Because reference intervals are defined to include 95% of the values from a healthy reference population, there is a…

5% chance a healthy person will have a test value outside of the reference range

Sensitivity

Percentage of positive test results in patients with a particular disease

A sensitivity of 95% means that 95% of patients WITH the disease will have positive results, and…

5% of patients WITH the disease will have FALSE NEGATIVE results

Specificty

The percentage of negative results in patients WITHOUT a particular disease

A 95% specificity means that 95% of patients WITHOUT the disease will have a negative test, and…

5% of patients WITHOUT the disease will have a FALSE POSITIVE result

Prevalence

Percentage of general population with disease

• expressed as percentage or as number of people with disease per 100,000

Prevalence is equivalent to the __ of disease.

Pretest probability

Screening tests screen a population for the…

Presence of a particular disease

Screening test performed on unselected populations where disease prevalence is very low will yield…

Overwhelmingly false positive results

• Even if test has very high specificity

Long term diabetes complications (2)

1. Macrovascular disease

2. Microvascular disease

Macrovascular disease

Complications related to accelerated atherosclerosis in large to medium sized arteries

• most of excess mortality related to diabetes

Microvascular disease

Occurs in small arteries, arterioles, and capillaries

Microvascular disease Includes:

• Diabetic retinopathy

• Diabetic nephropathy

• Cardiac dysfunction

• Diabetic neuropathy

HbA1c is formed by…

non-enzymatic attachment of glucose to Hemoglobin

• slowly and continuous

HbAc1 is measured in __ or __ monitoring of glucose levels.

bimonthly; quarterly

Microalbuminuria

Excretion of 50-200 mg of albumin in 24 hrs

• early detection allows reversal of nephropathy

Once proteinuria has developed, treatment may ___ but will NOT reverse it.

Slow the progression of kidney disease

Common laboratory tests for diabetes (5)

• complete blood count

• Complete blood count with white count

• Serum chemistry

• Coagulation studies

• Urinalysis

Pre-test Probability

estimated likelihood a patient has a specific disease before a diagnostic test is performed