Urinalysis and Renal Disorders Flashcards

A 52-year-old commercial driver presents for DOT physical with a urine specific gravity of 1.003 and urine osmolality of 95 mOsm/kg. Serum sodium is 148 mEq/L. He denies excessive fluid intake. Which condition best explains this combination of findings?

Answer: Nephrogenic diabetes insipidus with renal ADH resistance

Nephrogenic diabetes insipidus (NDI) is characterized by the inability of the renal tubules to respond to ADH, resulting in dilute urine (low specific gravity, low osmolality) despite hypernatremia. Unlike central DI where exogenous ADH corrects the defect, NDI persists because the collecting duct receptors are unresponsive. Psychogenic polydipsia would cause dilute urine but also dilutional hyponatremia (not hypernatremia). Central DI would also produce dilute urine with hypernatremia, but ADH replacement would correct it. SIADH produces concentrated urine and hyponatremia—the opposite pattern.

During a DOT urinalysis, a driver's dipstick shows 2+ protein. Repeat testing one week later also shows 2+ protein. Urine protein-to-creatinine ratio is 0.45. eGFR is 61 mL/min/1.73m². Blood pressure is 148/92 mmHg. Under FMCSA standards, which finding is MOST critical in determining whether this driver can receive medical certification?

Answer: The presence of functional impairment affecting safe driving ability

FMCSA does not automatically disqualify drivers based on specific laboratory thresholds for proteinuria or eGFR alone. The regulatory standard requires that the medical examiner determine whether any underlying condition causes functional impairment that would affect the driver's ability to safely operate a commercial motor vehicle. CKD Stage 3a (eGFR 45–59) or even Stage 3b may still be compatible with certification if the driver is asymptomatic, well-controlled, and has no functional compromise. The examiner must assess the whole clinical picture, not just a single lab value.

A 45-year-old male truck driver has persistent microscopic hematuria (>5 RBCs/HPF on three separate specimens over 6 weeks) with dysmorphic red blood cells and RBC casts noted on urine microscopy. His blood pressure is 156/98 mmHg and eGFR is 72 mL/min/1.73m². The MOST likely diagnosis and the primary recommended next diagnostic step are:

Answer: IgA nephropathy; measure serum IgA levels and consider renal biopsy

Dysmorphic RBCs and RBC casts on urine microscopy are hallmarks of glomerular bleeding, localizing the source to the nephron rather than the urothelium. This pattern distinguishes glomerulonephritis from urothelial causes (cancer, stones, infection). In a middle-aged male with hypertension, proteinuria context, and glomerular hematuria, IgA nephropathy is the most common primary glomerulonephritis in adults worldwide. Definitive diagnosis requires renal biopsy showing mesangial IgA deposits on immunofluorescence. CT urogram and cystoscopy are appropriate for non-glomerular (isomorphic) hematuria to rule out urothelial malignancy.

A CDL applicant's urinalysis reveals glucose 2+ on dipstick, but fasting blood glucose is 88 mg/dL and HbA1c is 5.1%. Urine glucose-to-creatinine ratio is elevated. Which mechanism BEST explains isolated glucosuria without hyperglycemia in this driver?

Answer: Defective SGLT2 co-transporter in the proximal tubule with a lowered renal glucose threshold

Benign familial renal glucosuria results from loss-of-function variants in SGLT2 (SLC5A2), the sodium-glucose co-transporter responsible for reabsorbing ~90% of filtered glucose in the proximal tubule. When SGLT2 is defective, the renal threshold for glucose is markedly lowered (from the normal ~180 mg/dL), causing glucosuria even at euglycemic glucose levels. This is a benign condition requiring no treatment and does not represent diabetes. Fanconi syndrome would cause global proximal tubule dysfunction (phosphaturia, aminoaciduria, bicarbonaturia, uricosuria) in addition to glucosuria. The other options do not explain persistent euglycemic glucosuria.

A 38-year-old commercial driver is diagnosed with autosomal dominant polycystic kidney disease (ADPKD) after a family history prompted imaging. Current eGFR is 78 mL/min/1.73m², blood pressure is controlled at 130/82 mmHg on lisinopril, and he is asymptomatic. He drives a school bus and is requesting DOT certification. Which statement MOST accurately reflects his certification status?

Answer: He may be certified if he demonstrates no functional impairment; annual monitoring is recommended

ADPKD alone is not a per se disqualifying condition under FMCSA regulations. The medical examiner must assess whether the condition causes functional impairment affecting safe CMV operation. With preserved eGFR (Stage 2 CKD), controlled blood pressure, and no symptoms (e.g., severe pain episodes, cognitive effects from uremia), this driver may be certified. However, given the progressive nature of ADPKD and cardiovascular associations (intracranial aneurysms, valvular disease), annual recertification and closer monitoring are prudent. FMCSA standards apply to school bus drivers operating in interstate commerce; state laws may impose additional requirements but do not nullify federal standards.

On a DOT urinalysis, a driver's specimen has a specific gravity of 1.003, pH of 9.5, and dipstick is negative for all analytes. The specimen temperature at collection was 94°F (34.4°C). Under DOT 49 CFR Part 40 specimen validity rules, the collector's CORRECT action is:

Answer: Discard the specimen and direct a second collection under direct observation immediately

Under 49 CFR Part 40, a specimen temperature outside the range of 90–100°F (32–38°C) within 4 minutes of collection is a temperature out-of-range finding. At 94°F, this specimen is within the acceptable temperature range (barely — 90°F is the lower limit). However, the combination of very low specific gravity (1.003) and extremely alkaline pH (9.5) raises suspicion for adulteration or substitution. More critically: a pH ≥ 11.0 triggers a report to the MRO as adulterated; pH 9.5 is not an automatic invalidity trigger by itself, but the low specific gravity (below 1.010) may suggest substitution if creatinine is also < 2 mg/dL. The collector should send the specimen to the lab for full validity testing; if the lab confirms substitution (SG ≤ 1.001 AND creatinine ≤ 2 mg/dL), the MRO reports it as substituted. The collector's immediate action for a temperature flag is direct observed collection of a second specimen.