2 Laboratory and Specimen Tests

Purpose and reliability of laboratory tests

Laboratory tests examine blood, urine, stool, sputum, or other specimens to help screen for disease, support a diagnosis, or monitor health and treatment. Reliable results depend on appropriate preparation, correct patient identification, proper collection and handling, and interpretation alongside symptoms and medical history. A result outside the laboratory’s reference range does not, by itself, establish a diagnosis, and reference ranges can differ by laboratory and test method.

Preparation, identification, and patient communication

Follow the instructions for the specific test. Many tests require no special preparation, while some blood glucose or lipid tests may require fasting. The ordering clinician should specify whether fasting is needed and for how long. Plain water is generally allowed during a fast unless instructions say otherwise. Do not stop medicines or supplements unless directed by the clinician. Report medicines, vitamins, supplements, recent strenuous exercise, and any preparation instructions that could not be followed.

Use the required patient identifiers and label each specimen as directed. Include the collection date and time and, when relevant, the specimen source. Correct labeling and prompt handling help protect specimen integrity.

Explain what the sample is for, how it will be collected, what preparation is needed, and when or how results will be communicated. Invite questions, and ask about needle anxiety or a history of fainting before a blood draw.

Common blood tests

A Complete blood count (CBC) measures red cells, hemoglobin, hematocrit, white cells, and platelets. Low red-cell measures may occur with anemia. High or low white-cell counts and platelet counts have many possible causes and need clinical context. A CBC usually requires no special preparation unless another test collected at the same time requires it. A small needle prick, brief soreness, or bruising can occur.

A Basic or comprehensive metabolic panel (BMP/CMP) measures substances such as glucose and electrolytes. A comprehensive panel also includes proteins, liver-associated enzymes, bilirubin, and kidney-related measures such as BUN and creatinine. Results can provide clues about fluid and electrolyte balance and organ function, but do not identify a cause by themselves. Follow the ordering clinician’s instructions: fasting may be requested for some panels or accompanying tests, but do not assume it is required without instructions.

A glucose result reflects blood sugar at the time of collection. A1C estimates average blood sugar over roughly the prior three months. Fasting depends on the type of glucose test; A1C generally does not require fasting. Ask which test was ordered and follow its instructions.

A Blood culture looks for germs in the blood. A positive result may indicate bloodstream infection, but contamination during collection is also possible, so interpret it with the clinical picture and other cultures. When feasible, collect it before antimicrobial therapy, using careful sterile technique and the facility’s protocol.

Blood draw aftercare and possible complications

After venipuncture, apply firm pressure with the arm straight until bleeding stops, then keep the dressing in place as directed. Mild soreness or a small bruise may occur. Report persistent bleeding, increasing swelling, significant pain, faintness, or redness at the puncture site promptly. Possible complications include bruising or hematoma, light-headedness or fainting, and, rarely, infection.

Urine tests and collection

Urinalysis may include visual inspection, chemical dipstick testing, and microscopic examination. It can assess color and clarity, pH and concentration, and findings such as blood, protein, glucose, ketones, cells, casts, crystals, or bacteria. Nitrites or white blood cells can support concern for a urinary infection; blood or protein may prompt further assessment. None of these findings alone identifies the cause.

To collect a clean-catch midstream sample:

1. Wash and dry hands. Open the cup without touching its inside.

2. Clean the genital area as instructed. Keep the labia separated during collection, or retract the foreskin if present and clean the glans.

3. Begin urinating into the toilet. Without stopping the stream if possible, collect the midstream urine in the cup. Do not let the cup touch the body.

4. Cap the container and return it promptly as instructed. Tell the clinician if you are menstruating or have bleeding that could affect the sample.

A Urine culture checks for bacteria or yeast and may help identify the organism causing infection. A clean-catch specimen is commonly used; follow collection and transport instructions carefully. “No growth” is generally a normal result, while growth may indicate infection. Interpret the result with symptoms and collection quality. Some cultures require a day or more for results.

For a timed or 24-hour urine collection, follow the supplied container and storage instructions exactly. The start and end times matter, and the collection generally requires saving every void during the specified period. If a sample is missed or spilled, contact the laboratory or clinician for instructions rather than guessing whether to continue.

Stool and sputum specimens

Collect stool in the supplied kit or a clean, dry container. Avoid mixing it with urine or toilet water, and label and return it as instructed. Some guaiac fecal occult blood tests require avoiding certain foods, supplements, or medicines; requirements vary by test. Do not stop prescribed medicines without medical advice. A positive occult-blood result means blood was detected, not that cancer is diagnosed; follow-up may be needed to identify the cause.

Sputum is mucus coughed up from the lower airways, not saliva. For a sputum culture, rinse the mouth with water if instructed, breathe deeply, and cough deeply into the sterile container. The culture may identify bacteria or fungi. Results may take days or longer and must be interpreted with symptoms and other findings. Do not stop antibiotics unless instructed.

Interpreting and explaining results

Interpret results using the units and reference interval printed on the report; intervals vary among laboratories. Consider whether preparation, medicines, hydration, recent activity, menstruation, or collection quality may have affected the result.

Interpret findings with symptoms, medical history, examination, and other tests rather than in isolation. A result marked high or low may be temporary or clinically unimportant, while a result within range does not always rule out disease. Explain the next step clearly, whether that is repeat testing, additional evaluation, treatment, or no immediate action. Encourage patients to ask the ordering clinician what their individual results mean.

• Clean-catch midstream collection