MLPAO MLPAO Medical Laboratory Calculations 1 — Questions and Answers
Question 1: A patient's serum glucose is reported as 5.6 mmol/L. What is the equivalent value in mg/dL?
- 100.8 mg/dL (Correct answer)
- 56.0 mg/dL
- 112.0 mg/dL
- 89.6 mg/dL
Correct answer: 100.8 mg/dL
To convert mmol/L to mg/dL for glucose, multiply by 18.016 (the molecular weight factor). 5.6 × 18.016 = 100.9 mg/dL ≈ 100.8 mg/dL.
Glucose has a molecular weight of 180.16 g/mol. The conversion factor from mmol/L to mg/dL is MW/10 = 180.16/10 = 18.016. Therefore: 5.6 mmol/L × 18.016 = 100.89 mg/dL ≈ 100.8 mg/dL. This is within the normal fasting range (3.9–6.1 mmol/L or 70–110 mg/dL). In Ontario laboratories, results are commonly reported in mmol/L per SI conventions.
Question 2: You need to prepare a 1:10 dilution of a patient serum sample. If the final volume required is 5 mL, how much serum do you need?
- 0.5 mL (Correct answer)
- 1.0 mL
- 0.1 mL
- 2.5 mL
Correct answer: 0.5 mL
A 1:10 dilution means 1 part sample in 10 parts total. Serum needed = 5 mL ÷ 10 = 0.5 mL, with 4.5 mL diluent.
For a 1:10 dilution, the formula is: Volume of sample = Final volume ÷ Dilution factor. Here: 5 mL ÷ 10 = 0.5 mL of serum. The diluent volume = 5 mL − 0.5 mL = 4.5 mL. This is a common dilution used when analyte concentrations exceed the linear range of the assay. In Ontario lab practice, always verify the dilution is within the assay's validated dilution range before reporting.
Question 3: A urine specific gravity reading is 1.025. Which of the following best describes this specimen?
- Concentrated urine with high solute content (Correct answer)
- Dilute urine with low solute content
- Normal hydration status
- Hemolyzed specimen requiring recollection
Correct answer: Concentrated urine with high solute content
Specific gravity of 1.025 is at the high end of the normal range (1.001–1.030), indicating concentrated urine with high solute content, suggesting dehydration or ADH activity.
Urine specific gravity measures the density of urine compared to water (1.000). The normal range is 1.001–1.030. A value of 1.025 indicates concentrated urine, which typically reflects adequate ADH secretion, dehydration, or high protein/glucose content. Values above 1.030 may suggest the presence of contrast media or very high protein. In Ontario urinalysis reporting per CSMLS/MLPAO standards, specific gravity is routinely measured with a refractometer or automated dipstick analyzer.
Question 4: A laboratory uses a control with a target value of 4.0 mmol/L and a standard deviation (SD) of 0.1 mmol/L. What is the 2-SD warning limit?
- 3.8–4.2 mmol/L (Correct answer)
- 3.9–4.1 mmol/L
- 3.7–4.3 mmol/L
- 4.0–4.2 mmol/L
Correct answer: 3.8–4.2 mmol/L
The 2-SD warning limits are: mean ± 2SD = 4.0 ± 2(0.1) = 4.0 ± 0.2, giving a range of 3.8–4.2 mmol/L.
In Westgard QC rules, the 2s warning rule (1₂s) triggers a warning when a control value falls outside mean ± 2 SD. Calculation: Lower limit = 4.0 − (2 × 0.1) = 3.8 mmol/L; Upper limit = 4.0 + (2 × 0.1) = 4.2 mmol/L. This is a warning, not a rejection. Ontario labs follow ISO 15189 and IQMH guidelines which require documented QC procedures including Westgard rules application.
Question 5: A blood specimen collected in a plain red-top tube at 9:00 AM must be centrifuged within 30 minutes of collection. What is the latest acceptable centrifugation time?
- 9:30 AM (Correct answer)
- 9:45 AM
- 10:00 AM
- 9:15 AM
Correct answer: 9:30 AM
Adding 30 minutes to the 9:00 AM collection time gives 9:30 AM as the deadline for centrifugation.
Serum separator tubes (SST) and plain red-top tubes require clot formation before centrifugation, typically 20–30 minutes at room temperature. The specimen must be centrifuged within 30 minutes of collection (or per manufacturer specifications) to prevent cellular metabolism from altering analyte concentrations—especially glucose, potassium, and lactate. In Ontario, pre-analytical specimen handling requirements follow CSMLS standards and laboratory SOPs. Documentation of collection time and centrifugation time is essential for audit purposes.
Question 6: A technologist performs a serial dilution starting with a 1:2 dilution, followed by three additional 1:2 dilutions. What is the final dilution factor of the last tube?
- 1:16 (Correct answer)
- 1:8
- 1:32
- 1:10
Correct answer: 1:16
Each 1:2 dilution doubles the dilution factor. After 4 sequential 1:2 dilutions: 2¹ × 2¹ × 2¹ × 2¹ = 2⁴ = 1:16.
In a serial dilution, each step multiplies the cumulative dilution. Starting with 1:2: Step 1 = 1:2; Step 2 = 1:4; Step 3 = 1:8; Step 4 = 1:16. The final tube represents a 1:16 dilution of the original specimen. Serial dilutions are used in microbiology MIC testing, serology titres, and hematology studies. In Ontario medical labs, serial dilutions for antibody titres (e.g., ANA, ASO) must be documented with each dilution step recorded.
Question 7: A urinalysis dipstick shows a glucose reading of 2+ and protein reading of trace. What should the technologist do next?
- Confirm with a microscopic examination and notify the physician if glucose is significantly elevated (Correct answer)
- Report the results immediately without further testing
- Repeat only the protein test on a new dipstick
- Discard the specimen and request a new sample
Correct answer: Confirm with a microscopic examination and notify the physician if glucose is significantly elevated
Abnormal dipstick findings (glucose 2+) require correlation with microscopy and clinical context. The physician should be alerted if findings are clinically significant.
Per MLPAO and CSMLS urinalysis guidelines, a positive glucose result (2+) indicates glucosuria, which may signal diabetes mellitus, renal glycosuria, or Fanconi syndrome. The technologist should perform a microscopic examination to assess for casts, crystals, and cells that may clarify the clinical picture. Critical or unexpected results require timely notification of the requesting physician per Ontario lab reporting requirements and the Public Hospitals Act. Trace protein may be physiological but combined with 2+ glucose warrants clinical correlation.
MLPAO MLPAO Medical Laboratory Calculations 1
A patient's serum glucose is reported as 5.6 mmol/L.
What is the equivalent value in mg/dL?