p2cc

Question 1

A pre-analytical error can be introduced by:

A. Drawing a coagulation tube before an EDTA tube
B. Mixing an EDTA tube 8 to 10 times
C. Transporting the specimen in a biohazard bag
D. Vigorously shaking the blood tube to prevent clotting

Answer 1

D. Vigorously shaking the blood tube to prevent clotting

Feedback

Vigorously mixing can cause hemolysis

Question 2

In quality control, ± 2 standard deviations from the mean includes what percentage of the sample population?
A. 50%
B. 75%
C. 95%
D. 98%

Answer 2

D. 95%

Feedback

The probability of an observation having a value within ± 2 standard deviations of the mean in a normal distribution is 95%.

Question 3

The acceptable limit of error in the chemistry laboratory is 2 standard deviations. If you run the normal control of 100 times, how many of the values would be out of the control range due to random error?

A. 1
B. 5
C. 10
D. 20

Answer 3

B. 5

Feedback

The probability of an observation having a value of 2 SD from the mean in a normal distribution is 95.5%. Therefore, 5 control values out of 100 would be out of control due to random error.

Question 4

The following data were calculated on a series of 30 determinations of serum uric acid control: mean = 5.8 mg/dL, 1 standard deviation = 0.15 mg/dL. If confidence limits are set at ± 2 SD, which o f the following represents allowable limits for the control?

A. 5.65 to 5.95 mg/dL
B. 5.35 to 6.25 mg/dL
C. 5.50 to 6.10 mg/dL
D. 5.70 to 5.90 mg/dL

Answer 4

C. 5.50 to 6.10 mg/dL

Feedback

Standard deviation is a measure of the dispersion of data around the mean.

Question 5

A delta check is a method that:

A. Determines the mean and variance of an instrument
B. Monitors the testing system for precision
C. Monitors patient sample day by day
D. Is determined by each laboratory facility

Answer 5

C. Monitors patient sample day by day

Feedback

The delta check method compares current results from automated analyzers with the result from the most recent, previous values for the same patient

Question 6

Measures of Center
Choose 3

A. Coefficient of variation
B. Mean
C. Median
D. Mode
E. Range
F. Standard deviation

Answer 6

B,C,D

Feedback

The three most commonly used descriptions of the center of a dataset are the mean, the median, and the mode.

Question 7

Measures of spread
Choose 3

A. Coefficient of variation
B. Mean
C. Median
D. Mode
E. Range
F. Standard deviation

Answer 7

A,E,F

Feedback

The spread represents the relationship of all the data points to the mean. There are three commonly used descriptions of spread: (1) range (2) standard deviation (SD), and (3) coefficient of variation (CV).

Question 8

Systematic errors
Choose 3

A. Calibrator reconstitution
B. Electro-optical mechanism
C. Environmental conditions
D. Fluctuations in line voltage
E. Instability of instrument
F. Reagent dispensing
G. Reagent lot variability
H. Sample evaporation
I. Temperature of analyzer
J. Variation in handling techniques: pipetting, mixing, timing
K. Variation in operators
L. Wear and tear of instrument

Answer 8

D,G,L

Feedback

Reference: Clinical Chemistry: A Laboratory Perspective [Arneson]

A SYSTEMATIC ERROR, on the other hand, will be seen as a trend in the data. Control values gradually rise (or fall) from the previously established limits. This type of error includes improper calibration, deterioration of reagents, sample instability, instrument drift, or changes in standard materials. All the Westgard rules that indicate trends identify systematic errors. 2(2S), 4(1S) and 10(x) rule.

SYSTEMATIC ERRORS MAY BE DUE TO:

Aging reagents
Aging calibrators
Instrument components
Optical changes
Fluctuations in line voltage
Wear and tear of instrument
Reagent lot variability
Calibration differences
Technologist interactions

Question 9

Random Errors
Choose 3

A. Aging reagents
B. Aging calibrators
C. Calibration differences
D. Instrument components
E. Fluctuations in line voltage
F. Optical changes
G. Reagent lot variability
H. Reagent dispensing
I. Technologist interactions
J. Variation in handling techniques: pipetting, mixing, timing
K. Variation in operator
L. Wear and tear of instrument

Answer 9

H,J,K

Feedback

Reference: Clinical Chemistry: A Laboratory Perspective [Arneson]

RANDOM ERROR is one with no trend or means of predicting it. Random errors include such situations as mislabeling a sample, pipetting errors, improper mixing of sample and reagent, voltage fluctuations not compensated for by instrument circuitry, and temperature fluctuations. Violations of the 1(2S), 1(3S) and R(4S) Westgard rules are usually associated with random error. To assess the situation, the sample is assayed using the same reagents. If a random error occurred, the same mistake may not be made again, and the result will be within appropriate control limits.

RANDOM ERRORS MAY BE DUE TO:
Reagent dispensing
Sample evaporation
Temperature of analyzer
Electro-optical mechanism
Calibrator reconstitution
Environmental conditions
Instability of instrument
Variation in handling techniques: pipetting, mixing, timing
Variation in operators

Question 10

Most frequently occurring value in a dataset:

A. Mean
B. Median
C. Mode
D. Range

Answer 10

C. Mode

Feedback

The mode is the most frequently occurring value in a dataset. Although it is seldom used to describe data, it is referred to when in reference to the shape of data, a bimodal distribution, for example.

Question 11

Type of systemic error in the sample direction and magnitude; the magnitude of change is constant and not dependent on the amount of analyte.

A. Constant systematic error
B. Proportional systematic error

Answer 11

A. Constant systematic error

Feedback

Constant error: Type of systemic error in the sample direction and magnitude; the magnitude of change is constant and not dependent on the amount of analyte.

Proportional error: Type of systemic error where the magnitude changes as a percent of the analyte present; error dependent on analyte concentration.

Question 12

Type of systemic error where the magnitude changes as a percent of the analyte present; error dependent on analyte concentration.

A. Constant systematic error
B. Proportional systematic error

Answer 12

B. Proportional systematic error

Feedback

Constant error: Type of systemic error in the sample direction and magnitude; the magnitude of change is constant and not dependent on the amount of analyte.

Proportional error: Type of systemic error where the magnitude changes as a percent of the analyte present; error dependent on analyte concentration.

Question 13

Difference between the observed mean and the reference mean:

A. Bias
B. Confidence interval
C. Parametric method
D. Nonparametric method

Answer 13

A. Bias

Feedback

Bias: Difference between the observed mean and the reference mean.

Negative bias indicates that the test values tend to be lower than the reference value, whereas positive bias indicates test values are generally higher.

Bias is a type of constant systematic error.

Question 14

Ability of a test to detect a given disease or condition.

A. Analytic sensitivity
B. Analytic specificity
C. Diagnostic sensitivity
D. Diagnostic specificity

Answer 14

C. Diagnostic sensitivity

Feedback

Analytic sensitivity: Ability of a method to detect small quantities of an analyte.

Analytic specificity: Ability of a method to detect only the analyte it is designed to determine.

Diagnostic sensitivity: Ability of a test to detect a given disease or condition.

Diagnostic specificity: Ability of a test to correctly identify the absence of a given disease or condition.

Question 15

Ability of a test to correctly identify the absence of a given disease or condition.

A. Analytic sensitivity
B. Analytic specificity
C. Diagnostic sensitivity
D. Diagnostic specificity

Answer 15

D. Diagnostic specificity

Feedback

Analytic sensitivity: Ability of a method to detect small quantities of an analyte.

Analytic specificity: Ability of a method to detect only the analyte it is designed to determine.

Diagnostic sensitivity: Ability of a test to detect a given disease or condition.

Diagnostic specificity: Ability of a test to correctly identify the absence of a given disease or condition.

Question 16

Ability of a method to detect small quantities of an analyte.

A. Analytic sensitivity
B. Analytic specificity
C. Diagnostic sensitivity
D. Diagnostic specificity

Answer 16

A. Analytic sensitivity

Feedback

Analytic sensitivity: Ability of a method to detect small quantities of an analyte.

Analytic specificity: Ability of a method to detect only the analyte it is designed to determine.

Diagnostic sensitivity: Ability of a test to detect a given disease or condition.

Diagnostic specificity: Ability of a test to correctly identify the absence of a given disease or condition.

Question 17

Ability of a method to detect only the analyte it is designed to determine.

A. Analytic sensitivity
B. Analytic specificity
C. Diagnostic sensitivity
D. Diagnostic specificity

Answer 17

B. Analytic specificity

Feedback

Analytic sensitivity: Ability of a method to detect small quantities of an analyte.

Analytic specificity: Ability of a method to detect only the analyte it is designed to determine.

Diagnostic sensitivity: Ability of a test to detect a given disease or condition.

Diagnostic specificity: Ability of a test to correctly identify the absence of a given disease or condition.

Question 18

Positive predictive value:

A. Ability of a test to detect a given disease or condition.
B. Ability of a test to correctly identify the absence of a given disease or condition.
C. Chance of an individual having a given disease or condition if the test is abnormal.
D. Chance an individual does not have a given disease or condition if the test is within the reference interval.

Answer 18

C. Chance of an individual having a given disease or condition if the test is abnormal.

Feedback

Positive predictive value: Chance of an individual having a given disease or condition if the test is abnormal.

Negative predictive value: Chance an individual does not have a given disease or condition if the test is within the reference interval.

Question 19

Negative predictive value:

A. Ability of a test to detect a given disease or condition.
B. Ability of a test to correctly identify the absence of a given disease or condition.
C. Chance of an individual having a given disease or condition if the test is abnormal.
D. Chance an individual does not have a given disease or condition if the test is within the reference interval.

Answer 19

D. Chance an individual does not have a given disease or condition if the test is within the reference interval.

Question 20

What percentage of values will fall between ±2 s in a Gaussian (normal) distribution?

A. 34.13%
B. 68.26%
C. 95.45%
D. 99.74%

Answer 20

C. 95.45%

Feedback

68.26% will lie within ±1 s
95.45% will lie within ±2 s
99.74% will lie within ±3 s

Question 21

Two (2) consecutive control values exceed the same 2 standard deviation limit:

A. 1:2S
B. 2:2S
C. R:4S
D. 4:1S

Answer 21

B. 2:2S

Feedback

Westgard multirule is a control procedure that utilizes control rules to assess numerical quality control data; the control rules establish the limits for data rejection in a system with two controls. Other rules apply when three controls are used.

1:2s = 1 control value exceeds the mean ±2 standard deviations; warning rule that triggers inspection of control values using the other rejection rules that follow; only rule that is not used to reject a run; results are reportable

1:3s = 1 control value exceeds the mean ±3 standard deviations; detects random error

2:2s = 2 consecutive control values exceed the same 2 standard deviation limit (same mean +2 s or same mean -2 s); detects systematic error

R:4s = 1 control value in a group exceeds the mean +2 s and a second control value exceeds the mean -2 s, creating a 4 standard deviation spread; detects random error

4:ls = 4 consecutive control values are recorded on one side of the mean and exceed either the same mean +1 s or the same mean -1 s; detects systematic error

10:x =10 consecutive control values are recorded on one side of the mean (either above or below the mean); detects systematic error

Question 22

The term R:4S means that:

A. Four consecutive controls are greater than ±1 standard deviation from the mean
B. Two controls in the same run are greater than 4s units apart
C. Two consecutive controls in the same run are each greater than ±4s from the mean
D. There is a shift above the mean for four consecutive controls

Answer 22

B. Two controls in the same run are greater than 4s units apart

Feedback

The R:4s rule is applied to two control levels within the same run. The rule is violated when the algebraic difference between them (level 1 –
level 2) exceeds 4s.

The R:4s rule detects random error (error due to poor precision).

Question 23

Error always in one direction:

A. Random error
B. Systematic error

Answer 23

B. Systematic error

Feedback

Systemic error: Error always in one direction.

Random error: Error varies from sample to sample.

Question 24

Which of the following terms refers to deviation from the true value caused by indeterminate errors inherent in every laboratory measurement?

A. Random error
B. Standard error of the mean
C. Parametric analysis
D. Nonparametric analysis

Answer 24

A. Random error

Feedback

Random errors are deviations from the true value caused by unavoidable errors inherent in laboratory measurements.

The standard error of the mean is a statistical concept reflecting sampling variation. It is the standard deviation of the entire population.

Parametric statistics refer to a Gaussian (normal) distribution of data.

Nonparametric statistics are more general and require no assumptions.

Question 25

A trend in QC results is most likely caused by:

A. Deterioration of the reagent
B. Miscalibration of the instrument
C. Improper dilution of standards
D. Electronic noise

Answer 25

A. Deterioration of the reagent

Question 26

Which of the following plots is best for detecting all types of QC errors?

A. Levy–Jennings
B. Tonks–Youden
C. Cusum
D. Linear regression

Answer 26

A. Levy–Jennings

Feedback

The Levy–Jennings plot is a graph of all QC results with concentration plotted on the y axis and run number on the x axis.

Question 27

Which of the following plots is best for comparison of precision and accuracy among laboratories?

A. Levy–Jennings
B. Tonks–Youden
C. Cusum
D. Linear regression

Answer 27

B. Tonks–Youden

Feedback

The Tonks–Youden plot is used for interlaboratory comparison of monthly means. The method mean for level 1 is at the center of the y axis and mean for level 2 at the center of the x axis. Lines are drawn from the means of both levels across the graph, dividing it into four equal quadrants. If a laboratory’s monthly means both plot in the lower left or upper right, then systematic error (SE) exists in its method.

Question 28

Which plot will give the earliest indication of a shift or trend?

A. Levy–Jennings
B. Tonks–Youden
C. Cusum
D. Histogram

Answer 28

C. Cusum

Feedback

Cusum points are the algebraic sum of the difference between each QC result and the mean. The y axis is the sum of differences and the x axis is the run number. The center of the y axis is 0. Because QC results follow a random distribution, the points should distribute about the zero line. Results are out of control when the slope exceeds 45° or a decision limit (e.g., ±2.7s) is exceeded.

Question 29

Which of the following terms refers to the closeness with which the measured value agrees with the true value?

A. Random error
B. Precision
C. Accuracy
D. Variance

Answer 29

C. Accuracy

Feedback

The accuracy of an analytical result is the closeness with which the measured value agrees with the true value.

Precision is reproducibility.

Accuracy and precision are independent, but it is the goal of the clinical laboratory to design methods that are both precise and accurate.

Question 30

Relatively easy to measure and maintain:

A. Accuracy
B. Precision
C. Sensitivity
D. Specificity

Answer 30

B. Precision

Feedback

Accuracy is easy to define but difficult to establish and maintain.

Precision is relatively easy to measure and maintain.

Question 31

Which of the following describes the ability of an analytical method to maintain both accuracy and precision over an extended period of time?

A. Reliability
B. Validity
C. Probability
D. Sensitivity

Answer 31

A. Reliability

Feedback

The reliability of an analytical procedure is its ability to maintain accuracy and precision over an extended period of time during which supplies, equipment, and personnel in the laboratory may change. It is often used interchangeably with the term “consistency.” It is the goal of every clinical laboratory to produce reliable results.

Question 32

Which of the following statistical tests is used to compare the means of two methods?

A. Student’s t test
B. F distribution
C. Correlation coefficient (r)
D. Linear regression analysis

Answer 32

A. Student’s t test

Feedback

T TEST: COMPARES MEANS, ACCURACY
F TEST: COMPARES S.D., PRECISION

Student’s t test is the ratio of mean difference to the standard error of the mean difference (bias/random error) and tests for a significant difference in means.

The F test is the ratio of variances and determines if one method is
significantly less precise.

Question 33

Only carbohydrate directly used for energy:

A. Glucose
B. Maltose
C. Fructose
D. Lactose

Answer 33

A. Glucose

Question 34

In a person with normal glucose metabolism, the blood glucose level usually increases rapidly after carbohydrates are ingested but returns to a normal level after:

A. 30 minutes
B. 45 minutes
C. 60 minutes (1 hour)
D. 120 minutes (2 hours)

Answer 34

D. 120 minutes (2 hours)

Question 35

Glucose measurements can be ____ mg/dL erroneously higher by reducing methods than by more accurate enzymatic methods.

A. 1 to 5 mg/dL
B. 5 to 15 mg/dL
C. 20 to 25 mg/dL
D. 30 to 35 mg/dL

Answer 35

B. 5 to 15 mg/dL

Feedback

Glucose measurements can be 5 to 15 mg/dL erroneously higher by reducing methods than by more accurate enzymatic methods.

Question 36

Select the enzyme that is most specific for beta D-glucose:

A. Glucose oxidase
B. Glucose-6-phosphate dehydrogenase
C. Hexokinase
D. Phosphohexose isomerase

Answer 36

A. Glucose oxidase

Feedback

Glucose oxidase is the most specific enzyme reacting with only beta D-glucose. Glucose oxidase converts beta D-glucose to gluconic acid.

Mutarotase may be added to the reaction to facilitate the conversion of alpha-D-glucose to beta-D-glucose.

Question 37

Select the coupling enzyme used in the hexokinase method for glucose:

A. Glucose dehydrogenase
B. Glucose-6-phosphatase
C. Glucose-6-phosphate dehydrogenase
D. Peroxidase

Answer 37

C. Glucose-6-phosphate dehydrogenase

Feedback

The hexokinase method is considered more accurate than the glucose oxidase methods because the coupling reaction using glucose-6-phosphate dehydrogenase is highly specific; therefore, it has less interference than the coupled glucose oxidase procedure.

Question 38

Which of the following is a potential source of error in the HEXOKINASE METHOD?

A. Galactosemia
B. Hemolysis
C. Sample collected in fluoride
D. Ascorbic acid

Answer 38

B. Hemolysis

Feedback

Hemolyzed samples require a serum blank correction (subtraction of the reaction rate with hexokinase omitted from the reagent).

Question 39

Gross hemolysis and extremely elevated bilirubin may cause ______ in HEXOKINASE RESULTS.

A. False increase
B. False decrease
C. No effect
D. Variable

Answer 39

B. False decrease

Feedback

Generally accepted as the reference method, hexokinase method is not affected by ascorbic acid or uric acid. Gross hemolysis and extremely elevated bilirubin may cause a false decrease in results.

Question 40

VERY LOW OR UNDETECTABLE C-peptide:

A. Type 1 diabetes mellitus
B. Type 2 diabetes mellitus

Answer 40

A. Type 1 diabetes mellitus

Question 41

DETECTABLE C-peptide:

A. Type 1 diabetes mellitus
B. Type 2 diabetes mellitus

Answer 41

B. Type 2 diabetes mellitus

Question 42

A 62-year-old patient presents to the physician with report of increased thirst and increased urination, particularly at night. The physician requests a series of tests over the next few days. The following data are received: RANDOM GLUCOSE: 186 mg/dL; FASTING GLUCOSE: 114 mg/dL; 2-HOUR OGTT: 153 mg/dL HbA1c: 5.9%. Which of the following conclusions may be made regarding these data?

A. Data represents normal glucose status
B. Data represents an impaired glucose status
C. Data represents the presence of insulinoma
D. Data represents diagnosis of diabetes

Answer 42

B. Data represents an impaired glucose status

Feedback

Resting plasma glucose
NORMAL <140
IMPAIRED 140 – 199
DIAGNOSTIC ≥ 200 mg/dL

Fasting plasma glucose
NORMAL <100
IMPAIRED 100 – 125
DIAGNOSTIC ≥ 126 mg/dL

2-hour OGTT
NORMAL <140
IMPAIRED 140 – 199
DIAGNOSTIC ≥ 200 mg/dL

HbA1c
NORMAL <5.7 %
IMPAIRED 5.7 – 6.4%
DIAGNOSTIC ≥ 6.5%

Question 43

What is the recommended cutoff value for adequate control of blood glucose in diabetics as measured by glycated hemoglobin?

A. 5%
B. 6.5%
C. 9.5%
D. 11%

Answer 43

B. 6.5%
Feedback

If the result is 6.5% or more, the treatment plan should be adjusted to achieve a lower level, and the test performed every 3 months until control is improved.

Question 44

A factor, other than average plasma glucose values, that can affect the HbA1c level is:

A. Serum ketone bodies
B. Red blood cell life span
C. Ascorbic acid intake
D. Increased triglyceride levels

Answer 44

B. Red blood cell life span

Feedback

Two factors determine the glycosylated hemoglobin levels: the average glucose concentration and the red blood cell life span.

If the red blood cell life span is decreased because of another disease state such as hemoglobinopathies, the hemoglobin will have less time to become glycosylated and the glycosylated hemoglobin level will be lower.

Question 45

LONG-TERM estimation of glucose concentration can be followed by measuring:

A.Glycosylated hemoglobin (HbA1c)
B. Fructosamine

Answer 45

A.Glycosylated hemoglobin (HbA1c)

Feedback

Long-term estimation of glucose concentration can be followed by measuring glycosylated hemoglobin (Hb A1c). A level of 8% or less is considered “good” glycemic control.

Because the average red blood cell lives approximately 120 days, the glycosylated hemoglobin level at any one time reflects the average blood glucose level over the previous 2 to 3 months. Therefore, measuring the glycosylated hemoglobin provides the clinician with a time-averaged picture of the patient’s blood glucose concentration over the past 3 months.

Question 46

Most widely used to assess SHORT-TERM (3 to 6 weeks) glycemic control:

A. Glycosylated hemoglobin (HbA1c)
B. Fructosamine

Answer 46

B. Fructosamine

Feedback

FRUCTOSAMINE: GLYCOSYLATED ALBUMIN

Fructosamine assays are the most widely used to assess short-term (3 to 6 weeks) glycemic control because the average half-life of the proteins is 2–3 weeks.

Question 47

Formation of glucose-6-phosphate from noncarbohydrate sources:

A. Glycolysis
B. Gluconeogenesis
C. Glycogenolysis
D. Glycogenesis

Answer 47

B. Gluconeogenesis

Feedback

Glycolysis
Metabolism of glucose molecule to pyruvate or lactate for production of energy

Gluconeogenesis
Formation of glucose-6-phosphate from noncarbohydrate sources

Glycogenolysis
Breakdown of glycogen to glucose for use as energy

Glycogenesis
Conversion of glucose to glycogen for storage

Lipogenesis
Conversion of carbohydrates to fatty acids

Lipolysis
Decomposition of fat

Question 48

HYPERGLYCEMIC FACTOR produced by the pancreas is:

A. Epinephrine
B. Glucagon
C. Growth hormone
D. Insulin

Answer 48

B. Glucagon

Feedback

Glucagon is the primary hormone responsible for increasing glucose levels. It is synthesized by the ALPHA-cells of islets of Langerhans in the pancreas and released during stress and fasting states.

ACTION OF GLUCAGON
Increases glycogenolysis: glycogen → glucose
Increases gluconeogenesis: fatty acids → acetyl-CoA → ketone, proteins → amino acids

Question 49

HYPOGLYCEMIC FACTOR produced by the pancreas is:

A. Epinephrine
B. Glucagon
C. Growth hormone
D. Insulin

Answer 49

D. Insulin

Feedback

Insulin is the only hormone that decreases glucose levels and can be referred to as a hypoglycemic agent.

Insulin is the primary hormone responsible for the entry of glucose into the cell. It is synthesized by the beta cells of islets of Langerhans in the pancreas.

It decreases plasma glucose levels by increasing the transport entry of glucose in muscle and adipose tissue by way of nonspecific receptors. It also regulates glucose by increasing glycogenesis, lipogenesis, and glycolysis and inhibiting glycogenolysis.

ACTION OF INSULIN
Increases glycogenesis and glycolysis: glucose → glycogen → pyruvate → acetyl-CoA
Increases lipogenesis
Decreases glycogenolysis

Question 50

What would an individual with CUSHING SYNDROME tend to exhibit?

A. Hyperglycemia
B. Hypoglycemia
C. Normal blood glucose level
D. Decreased 2-hour postprandial glucose

Answer 50

A. Hyperglycemia

Feedback

CORTISOL INCREASES BLOOD GLUCOSE.

Question 51

Symptoms of HYPOGLYCEMIA usually occur when blood glucose has fallen below ___ mg/dL.

A. Below 50 mg/dL
B. Below 60 mg/dL
C. Below 70 mg/dL
D. Below 80 mg/dL

Answer 51

A. Below 50 mg/dL

Question 52

Beta cell destruction, usually leading to absolute insulin deficiency:

A. Type 1 DM
B. Type 2 DM

Answer 52

A. Type 1 DM

Question 53

May range from predominantly insulin resistance with relative insulin deficiency to a predominantly secretory defect with insulin resistance:

A. Type 1 DM
B. Type 2 DM

Answer 53

B. Type 2 DM

Question 54

Usual dose of LACTOSE in the oral lactose tolerance test is:

A. 25 grams
B. 50 grams
C. 75 grams
D. 100 grams

Answer 54

B. 50 grams

Feedback

ORAL LACTOSE TOLERANCE TESTS, measuring the increase in plasma glucose or galactose following ingestion of lactose, have been used to diagnose lactase deficiency.